Retinal laminar architecture in human retinitis pigmentosa caused by Rhodopsin gene mutations

Peak Cone Density Predicted from Outer Segment Length Measured on Optical Coherence Tomography

PURPOSE

To compare peak cone density predicted from outer segment length measured on optical coherence tomography with direct measures of peak cone density from adaptive optics scanning light ophthalmoscopy.

METHODS

Data from 42 healthy participants with direct peak cone density measures and optical coherence tomography line scans available were used in this study. Longitudinal reflectivity profiles were analyzed using two methods of identifying the boundaries of the ellipsoid and interdigitation zones to estimate maximum outer segment length: peak-to-peak and the slope method. These maximum outer segment length values were then used to predict peak cone density using a previously described geometrical model. A comparison between predicted and direct peak cone density measures was then performed.

RESULTS

The mean bias between observers for estimating maximum outer segment length across methods was less than 2 µm. Cone density predicted from the peak-to-peak method against direct cone density measures showed a mean bias of 6,812 cones/mm2 with 50% of participants displaying a 10% difference or less between predicted and direct cone density values. Cone density derived from the slope method showed a mean bias of -17,929 cones/mm2 relative to direct cone density measures, with only 41% of participants demonstrating less than a 10% difference between direct and predicted cone density values.

CONCLUSION

Predicted foveal cone density derived from peak-to-peak outer segment length measurements using commercial optical coherence tomography show modest agreement with direct measures of peak cone density from adaptive optics scanning light ophthalmoscopy. The methods used here are imperfect predictors of cone density, however, further exploration of this relationship could reveal a clinically relevant marker of cone structure.

Deep Learning-Based Retinal Layer Segmentation in Optical Coherence Tomography Scans of Patients with Inherited Retinal Diseases

BACKGROUND

In optical coherence tomography (OCT) scans of patients with inherited retinal diseases (IRDs), the measurement of the thickness of the outer nuclear layer (ONL) has been well established as a surrogate marker for photoreceptor preservation. Current automatic segmentation tools fail in OCT segmentation in IRDs, and manual segmentation is time-consuming.

METHODS AND MATERIAL

Patients with IRD and an available OCT scan were screened for the present study. Additionally, OCT scans of patients without retinal disease were included to provide training data for artificial intelligence (AI). We trained a U-net-based model on healthy patients and applied a domain adaption technique to the IRD patients' scans.

RESULTS

We established an AI-based image segmentation algorithm that reliably segments the ONL in OCT scans of IRD patients. In a test dataset, the dice score of the algorithm was 98.7%. Furthermore, we generated thickness maps of the full retinal thickness and the ONL layer for each patient.

CONCLUSION

Accurate segmentation of anatomical layers on OCT scans plays a crucial role for predictive models linking retinal structure to visual function. Our algorithm for segmentation of OCT images could provide the basis for further studies on IRDs.

Deep Learning-Assisted Measurements of Photoreceptor Ellipsoid Zone Area and Outer Segment Volume as Biomarkers for Retinitis Pigmentosa

The manual segmentation of retinal layers from OCT scan images is time-consuming and costly. The deep learning approach has potential for the automatic delineation of retinal layers to significantly reduce the burden of human graders. In this study, we compared deep learning model (DLM) segmentation with manual correction (DLM-MC) to conventional manual grading (MG) for the measurements of the photoreceptor ellipsoid zone (EZ) area and outer segment (OS) volume in retinitis pigmentosa (RP) to assess whether DLM-MC can be a new gold standard for retinal layer segmentation and for the measurement of retinal layer metrics. Ninety-six high-speed 9 mm 31-line volume scans obtained from 48 patients with RPGR-associated XLRP were selected based on the following criteria: the presence of an EZ band within the scan limit and a detectable EZ in at least three B-scans in a volume scan. All the B-scan images in each volume scan were manually segmented for the EZ and proximal retinal pigment epithelium (pRPE) by two experienced human graders to serve as the ground truth for comparison. The test volume scans were also segmented by a DLM and then manually corrected for EZ and pRPE by the same two graders to obtain DLM-MC segmentation. The EZ area and OS volume were determined by interpolating the discrete two-dimensional B-scan EZ-pRPE layer over the scan area. Dice similarity, Bland-Altman analysis, correlation, and linear regression analyses were conducted to assess the agreement between DLM-MC and MG for the EZ area and OS volume measurements. For the EZ area, the overall mean dice score (SD) between DLM-MC and MG was 0.8524 (0.0821), which was comparable to 0.8417 (0.1111) between two MGs. For the EZ area > 1 mm2, the average dice score increased to 0.8799 (0.0614). When comparing DLM-MC to MG, the Bland-Altman plots revealed a mean difference (SE) of 0.0132 (0.0953) mm2 and a coefficient of repeatability (CoR) of 1.8303 mm2 for the EZ area and a mean difference (SE) of 0.0080 (0.0020) mm3 and a CoR of 0.0381 mm3 for the OS volume. The correlation coefficients (95% CI) were 0.9928 (0.9892-0.9952) and 0.9938 (0.9906-0.9958) for the EZ area and OS volume, respectively. The linear regression slopes (95% CI) were 0.9598 (0.9399-0.9797) and 1.0104 (0.9909-1.0298), respectively. The results from this study suggest that the manual correction of deep learning model segmentation can generate EZ area and OS volume measurements in excellent agreement with those of conventional manual grading in RP. Because DLM-MC is more efficient for retinal layer segmentation from OCT scan images, it has the potential to reduce the burden of human graders in obtaining quantitative measurements of biomarkers for assessing disease progression and treatment outcomes in RP.

Deep Learning-Facilitated Study of the Rate of Change in Photoreceptor Outer Segment Metrics in RPGR-Related X-Linked Retinitis Pigmentosa

Purpose

The aim of this retrospective cohort study was to obtain three-dimensional (3D) photoreceptor outer segment (OS) metrics measurements with the assistance of a deep learning model (DLM) and to evaluate the longitudinal change in OS metrics and associated factors in retinitis pigmentosa GTPase regulator (RPGR) X-linked retinitis pigmentosa (XLRP).

Methods

The study included 34 male patients with RPGR-associated XLRP who had preserved ellipsoid zone (EZ) within their spectral-domain optical coherence tomography volume scans and an approximate 2-year or longer follow-up. Volume scans were segmented using a DLM with manual correction for EZ and apical retinal pigment epithelium (RPE). OS metrics were measured from 3D EZ-RPE layers of volume scans. Linear mixed-effects models were used to calculate the rate of change in OS metrics and the associated factors, including baseline age, baseline OS metrics, and follow-up duration.

Results

The mean (standard deviation) of progression rates were -0.28 (0.43) µm/y, -0.73 (0.61) mm2/y, and -0.014 (0.012) mm3/y for OS thickness, EZ area, and OS volume, respectively. In multivariable analysis, the progression rates of EZ area and OS volume were strongly associated with their baseline values, with faster decline in eyes with larger baseline values (P ≤ 0.003), and nonlinearly associated with the baseline age (P ≤ 0.003). OS thickness decline was not associated with its baseline value (P = 0.32).

Conclusions

These results provide evidence to support using OS metrics as biomarkers to assess the progression of XLRP and as the outcome measures of clinical trials. Given that their progression rates are dependent on their baseline values, the baseline EZ area and OS volume should be considered in the design and statistical analysis of future clinical trials. Deep learning may provide a useful tool to reduce the burden of human graders to analyze OCT scan images and to facilitate the assessment of disease progression and treatment trials for retinitis pigmentosa.

Photoreceptor function and structure in retinal degenerations caused by biallelic BEST1 mutations

The only approved retinal gene therapy is for biallelic RPE65 mutations which cause a recessive retinopathy with a primary molecular defect located at the retinal pigment epithelium (RPE). For a distinct recessive RPE disease caused by biallelic BEST1 mutations, a pre-clinical proof-of-concept for gene therapy has been demonstrated in canine eyes. The current study was undertaken to consider potential outcome measures for a BEST1 clinical trial in patients demonstrating a classic autosomal recessive bestrophinopathy (ARB) phenotype. Spatial distribution of retinal structure showed a wide expanse of abnormalities including large intraretinal cysts, shallow serous retinal detachments, abnormalities of inner and outer segments, and an unusual prominence of the external limiting membrane. Surrounding the central macula extending from 7 to 30 deg eccentricity, outer nuclear layer was thicker than expected from a cone only retina and implied survival of many rod photoreceptors. Co-localized however, were large losses of rod sensitivity despite preserved cone sensitivities. The dissociation of rod function from rod structure observed, supports a large treatment potential in the paramacular region for biallelic bestrophinopathies.

Investigation of Structural Alterations in Inherited Retinal Diseases: A Quantitative SD-OCT-Analysis of Retinal Layer Thicknesses in Light of Underlying Genetic Mutations

Inherited retinal diseases can result from various genetic defects and are one of the leading causes for blindness in the working-age population. The present study aims to provide a comprehensive description of changes in retinal structure associated with phenotypic disease entities and underlying genetic mutations. Full macular spectral domain optical coherence tomography scans were obtained and manually segmented in 16 patients with retinitis pigmentosa, 7 patients with cone−rod dystrophy, and 7 patients with Stargardt disease, as well as 23 age- and sex-matched controls without retinal disease, to assess retinal layer thicknesses. As indicated by generalized least squares models, all IRDs were associated with retinal thinning (p < 0.001), especially of the outer nuclear layer (ONL, p < 0.001). Except for the retinal nerve fiber layer, such thinning was associated with a reduced visual acuity (p < 0.001). These advances in our understanding of ultrastructural retinal changes are important for the development of gene-, cell-, and optogenetic therapy. Longitudinal studies are warranted to describe the temporal component of those changes.

Homeostatic plasticity in the retina

Vision begins in the retina, whose intricate neural circuits extract salient features of the environment from the light entering our eyes. Neurodegenerative diseases of the retina (e.g., inherited retinal degenerations, age-related macular degeneration, and glaucoma) impair vision and cause blindness in a growing number of people worldwide. Increasing evidence indicates that homeostatic plasticity (i.e., the drive of a neural system to stabilize its function) can, in principle, preserve retinal function in the face of major perturbations, including neurodegeneration. Here, we review the circumstances and events that trigger homeostatic plasticity in the retina during development, sensory experience, and disease. We discuss the diverse mechanisms that cooperate to compensate and the set points and outcomes that homeostatic retinal plasticity stabilizes. Finally, we summarize the opportunities and challenges for unlocking the therapeutic potential of homeostatic plasticity. Homeostatic plasticity is fundamental to understanding retinal development and function and could be an important tool in the fight to preserve and restore vision.

Gene Therapy for Rhodopsin Mutations

Mutations in RHO, the gene for rhodopsin, account for a large fraction of autosomal-dominant retinitis pigmentosa (adRP). Patients fall into two clinical classes, those with early onset, pan retinal photoreceptor degeneration, and those who experience slowly progressive disease. The latter class of patients are candidates for photoreceptor-directed gene therapy, while former may be candidates for delivery of light-responsive proteins to interneurons or retinal ganglion cells. Gene therapy for RHO adRP may be targeted to the mutant gene at the DNA or RNA level, while other therapies preserve the viability of photoreceptors without addressing the underlying mutation. Correcting the RHO gene and replacing the mutant RNA show promise in animal models, while sustaining viable photoreceptors has the potential to delay the loss of central vision and may preserve photoreceptors for gene-directed treatments.

Performance of Deep Learning Models in Automatic Measurement of Ellipsoid Zone Area on Baseline Optical Coherence Tomography (OCT) Images From the Rate of Progression of USH2A-Related Retinal Degeneration (RUSH2A) Study

Purpose

Previously, we have shown the capability of a hybrid deep learning (DL) model that combines a U-Net and a sliding-window (SW) convolutional neural network (CNN) for automatic segmentation of retinal layers from OCT scan images in retinitis pigmentosa (RP). We found that one of the shortcomings of the hybrid model is that it tends to underestimate ellipsoid zone (EZ) width or area, especially when EZ extends toward or beyond the edge of the macula. In this study, we trained the model with additional data which included more OCT scans having extended EZ. We evaluated its performance in automatic measurement of EZ area on SD-OCT volume scans obtained from the participants of the RUSH2A natural history study by comparing the model’s performance to the reading center’s manual grading.

Materials and Methods

De-identified Spectralis high-resolution 9-mm 121-line macular volume scans as well as their EZ area measurements by a reading center were transferred from the management center of the RUSH2A study under the data transfer and processing agreement. A total of 86 baseline volume scans from 86 participants of the RUSH2A study were included to evaluate two hybrid models: the original RP240 model trained on 480 mid-line B-scans from 220 patients with retinitis pigmentosa (RP) and 20 participants with normal vision from a single site, and the new RP340 model trained on a revised RP340 dataset which included RP240 dataset plus an additional 200 mid-line B-scans from another 100 patients with RP. There was no overlap of patients between training and evaluation datasets. EZ and apical RPE in each B-scan image were automatically segmented by the hybrid model. EZ areas were determined by interpolating the discrete 2-dimensional B-scan EZ-RPE layer over the scan area. Dice similarity, correlation, linear regression, and Bland-Altman analyses were conducted to assess the agreement between the EZ areas measured by the hybrid model and by the reading center.

Results

For EZ area &gt; 1 mm2, average dice coefficients ± SD between the EZ band segmentations determined by the DL model and the manual grading were 0.835 ± 0.132 and 0.867 ± 0.105 for RP240 and RP340 hybrid models, respectively (p &lt; 0.0005; n = 51). When compared to the manual grading, correlation coefficients (95% CI) were 0.991 (0.987–0.994) and 0.994 (0.991–0.996) for RP240 and RP340 hybrid models, respectively. Linear regression slopes (95% CI) were 0.918 (0.896–0.940) and 0.995 (0.975–1.014), respectively. Bland-Altman analysis revealed a mean difference ± SD of -0.137 ± 1.131 mm2 and 0.082 ± 0.825 mm2, respectively.

Conclusion

Additional training data improved the hybrid model’s performance, especially reducing the bias and narrowing the range of the 95% limit of agreement when compared to manual grading. The close agreement of DL models to manual grading suggests that DL may provide effective tools to significantly reduce the burden of reading centers to analyze OCT scan images. In addition to EZ area, our DL models can also provide the measurements of photoreceptor outer segment volume and thickness to further help assess disease progression and to facilitate the study of structure and function relationship in RP.

Retinal degeneration in humanized mice expressing mutant rhodopsin under the control of the endogenous murine promoter

RHO is one of the most common genetic causes of autosomal dominant retinitis Pigmentosa (adRP) and there is no effective therapy for this disease. While rapidly developed CRISPR/Cas9 gene editing technology presents a promising therapeutic strategy to treat adRP. A large number of studies for treating adRP using CRISPR/Cas9 have been performed based on transgenic mouse models which are affected with adRP caused by mutant mouse rhodopsin allele, the counterpart of human rhodopsin. Recently, some RHO humanized mouse models like T17M, P23H are generated, which permit testing of the therapeutic effect of CRISPR/Cas9 in preclinical in vivo systems, without putting humans at risk. While available humanized mouse models are few compared to the number of known RHO mutations, but it is time-consuming and costly to build humanized mice for each mutation. We wonder whether a humanized mouse model having several mutations simultaneously can be developed, although which rarely occurs in patients, to investigate the therapeutic effect of CRISPR/Cas9 for RHO-mediated adRP in preclinical in vivo systems. Homology directed repair strategy combing with CRISPR/Cas9 was employed to introduce human RHO genomic fragment containing the replacement of mouse exon1(mE1) after the start codon to mE5 before the stop codon and all introns by the human counterparts. The human rhodopsin could express under the control of the endogenous murine promoter both transcriptionally and translationally in vivo. Human rhodopsin in humanized mouse lines (without mutation) could replace murine rhodopsin morphologically and functionally. While human rhodopsin containing T17M, G51D, G114R, R135W and P171R mutations simultaneously in mutant humanized (Mut-Rho^wt/hum and Mut-Rho^hum/hum) mouse lines caused retinal degeneration. Mut-Rho^hum/hum mice suffered from severe retinal degeneration with defective formation of rod outer segment, leaving nonrecordable electroretinogram (ERG) at 3 months. Mut- Rho^wt/hum mice had a slower rate of photoreceptors loss. In 7-month-old Mut- Rho^wt/hum mice, statistically reduced scotopic ERG responses were visible compared with age-matched WT mice, but the shortened outer segment and thinner outer nuclear layer could be observed from 3 months. From 7 months to 9 months, significantly abnormal scotopic ERG responses were visible and photoreceptors loss were also obvious in 9-month-old Mut-Rho^wt/hum mice. In 12-month-old Mut- Rho^wt/hum mice, statistically reduced scotopic and photopic ERG responses and retinal degeneration throughout the retina were visible. Because scotopic responses were more affected than photopic responses in mutant humanized mice, demonstrating that rods dysfunction was more severe than cones dysfunction and deteriorated earlier, the pattern of retinal degeneration caused by mutant human rhodopsin was a typical rod-cone decay. Immunocytochemistry in cells indicated human rhodopsin proteins with 5 mutations aggregated in the cytoplasm and were also retained in the endoplasmic reticulum. The mutant human rhodopsin also accumulated in rod inner segments and cellular bodies in vivo. In conclusion, our humanized models provide excellent opportunities to study the human rhodopsin expression patterns. Our mutant humanized heterozygotes can provide opportunities to explore gene editing therapies via CRISPR/Cas9 for these five mutations in preclinical studies, it is time-saving and cost-effective.

A Hybrid Model Composed of Two Convolutional Neural Networks (CNNs) for Automatic Retinal Layer Segmentation of OCT Images in Retinitis Pigmentosa (RP)

Purpose

We propose and evaluate a hybrid model composed of two convolutional neural networks (CNNs) with different architectures for automatic segmentation of retina layers in spectral domain optical coherence tomography (SD-OCT) B-scans of retinitis pigmentosa (RP).

Methods

The hybrid model consisted of a U-Net for initial semantic segmentation and a sliding-window (SW) CNN for refinement by correcting the segmentation errors of U-Net. The U-Net construction followed Ronneberger et al. (2015) with an input image size of 256 × 32. The SW model was similar to our previously reported approach. Training image patches were generated from 480 horizontal midline B-scans obtained from 220 patients with RP and 20 normal participants. Testing images were 160 midline B-scans from a separate group of 80 patients with RP. The Spectralis segmentation of B-scans was manually corrected for the boundaries of the inner limiting membrane, inner nuclear layer, ellipsoid zone (EZ), retinal pigment epithelium, and Bruch's membrane by one grader for the training set and two for the testing set. The trained U-Net and SW, as well as the hybrid model, were used to classify all pixels in the testing B-scans. Bland–Altman and correlation analyses were conducted to compare layer boundary lines, EZ width, and photoreceptor outer segment (OS) length and area determined by the models to those by human graders.

Results

The mean times to classify a B-scan image were 0.3, 65.7, and 2.4 seconds for U-Net, SW, and the hybrid model, respectively. The mean ± SD accuracies to segment retinal layers were 90.8% ± 4.8% and 90.7% ± 4.0% for U-Net and SW, respectively. The hybrid model improved mean ± SD accuracy to 91.5% ± 4.8% (P < 0.039 vs. U-Net), resulting in an improvement in layer boundary segmentation as revealed by Bland–Altman analyses. EZ width, OS length, and OS area measured by the models were highly correlated with those measured by the human graders (r > 0.95 for EZ width; r > 0.83 for OS length; r > 0.97 for OS area; P < 0.05). The hybrid model further improved the performance of measuring retinal layer thickness by correcting misclassification of retinal layers from U-Net.

Conclusions

While the performances of U-Net and the SW model were comparable in delineating various retinal layers, U-Net was much faster than the SW model to segment B-scan images. The hybrid model that combines the two improves automatic retinal layer segmentation from OCT images in RP.

Translational Relevance

A hybrid deep machine learning model composed of CNNs with different architectures can be more effective than either model separately for automatic analysis of SD-OCT scan images, which is becoming increasingly necessary with current high-resolution, high-density volume scans.

ENHANCED S-CONE SYNDROME: VISUAL FUNCTION, CROSS-SECTIONAL IMAGING, AND CELLULAR STRUCTURE WITH ADAPTIVE OPTICS OPHTHALMOSCOPY

PURPOSE

To describe in detail the phenotype of a patient with enhanced S-cone syndrome.

METHODS

We describe a 13-year-old boy who presented with blurred vision, vitreous cells, cystoid macular edema refractory to steroid treatment, and a negative uveitic workup. The patient underwent a complete ophthalmic examination, full-field electroretinograms (ffERG), automatic static perimetry and multimodal imaging with spectral domain optical coherence tomography, and adaptive optics scanning laser ophthalmoscopy (AOSLO).

RESULTS

Spectral domain optical coherence tomography demonstrated cystoid macular edema and a hyperthick, delaminated midperipheral retina. Fluorescein angiography did not demonstrate macular leakage. Rod-mediated ffERGs were undetectable, and there was a supernormal response to short-wavelength stimuli compared with photopically matched longer wavelengths of light consistent with enhanced S-cone syndrome. Gene screening was positive for compound heterozygous mutations NR2E3: a known (c.119-2 A>C) and a novel (c.119-1G>A) mutation. By perimetry, sensitivities were normal or above normal for short-wavelength stimuli; there was no detectable rod-mediated vision. AOSLO demonstrated higher than normal cone densities in the perifoveal retina and evidence for smaller outer segment cone diameters.

CONCLUSION

Evidence for supernumerary cones (at least twice the normal complement) by AOSLO and spectral domain optical coherence tomography was associated with supernormal S-cone sensitivities and electroretinogram responses confirming previous in vivo findings in postmortem human specimens. Smaller than normal cones in enhanced S-cone syndrome may represent "hybrid" photoreceptors analogous to the rd7/rd7 murine model of the disease.

OCT Imaging in Infants

Optical coherence tomography (OCT) is widely applied in diagnosis and management of retina diseases particularly macular diseases in adult retina practices. However, it has been under-utilized in pediatric retinal diseases especially in neonates and infants. Utilization of OCT in primary macular diseases in this age group is also uncommon and is less reported. Challenges involved in image acquisition and limitations with available devices technique can explain the limited research and accurate data availability in the literature in this field. Purpose of this review article is to summarize the use of OCT and its importance in various infantile retinal pathologies such as vascular diseases, tumors, retinal dystrophies, and optic nerve pathologies with primary focus on neonates and infants, along with infant choroid. In addition, we also discuss about future directions including OCT angiography for infants.

Compound Heterozygous Mutations in ZNF408 in a Patient with a Late Onset Pigmentary Retinopathy and Relatively Preserved Central Retina

PURPOSE

To describe in detail the phenotype of a patient with compound heterozygous mutations in ZNF408 and an adult-onset pigmentary retinopathy rather than familial exudative vitreoretinopathy as expected with heterozygous mutations in this gene.

METHODS

A 70-year-old male presented with a pigmentary retinopathy, which prompted a genetic evaluation that revealed two variants in trans in the ZNF408 gene. He underwent an ophthalmic examination, kinetic fields, electroretinography (ERG), spectral-domain optical coherence tomography (SD-OCT), fundus autofluorescence, wide-angle fluorescein angiography and near-infrared imaging.

RESULTS

Visual acuity was 20/20 for both eyes. Fundus examination showed epiretinal membrane, vascular attenuation and peripheral bone spicule pigmentation in both eyes. Fluorescein angiography showed no vascular anomalies in both eyes. Fundus autofluorescence showed a preserved island of fundus autofluorescence centrally. Visual field by kinetic perimetry (V-4e stimulus) showed generalized constriction to 40 degrees of eccentricity and by an I-4e target showed generalized constriction to 10 degrees of eccentricity. ERG showed detectable but reduced cone-mediated responses. SD-OCT demonstrated preserved outer nuclear layer thickness centrally, which decreased with eccentricity. Static perimetry showed substantial rod and cone sensitivities centrally that declined with eccentricity. A next-generation sequencing panel revealed bi-allelic variants (p.Arg567Ter; c.1699C > T and p.Leu566His; c.1697 T > A) in the ZNF408 gene.

CONCLUSIONS

ZNF408-associated retinal dystrophies can present with predominantly retinal findings and should be considered in the differential diagnosis of retinitis pigmentosa. Our study revealed a novel variant p.L566H, which to our knowledge has not previously been reported.

Shared Features in Retinal Disorders With Involvement of Retinal Pigment Epithelium

When using spectral domain optical coherence tomography (SD-OCT) to inform the status of outer retina, we have noted discrete hyperreflective lesions extending through photoreceptor-attributable bands that have a similar presentation in multiple retinal diseases. These lesions present as either corrugated thickenings of interdigitation zone and ellipsoid zone bands or in later stages as rectangular or pyramidal shaped foci that extend radially through photoreceptor cell-attributable bands. In ABCA4-related and peripherin-2/RDS-disease (PRPH2/RDS), monogenic forms of retinopathy caused by mutations in proteins expressed in photoreceptor cells, these punctate lesions colocalize with fundus flecks in en face images. In fundus albipunctatus and retinitis punctata albescens, diseases caused by mutations in genes (retinol dehydrogenase 5, RDH5; and retinaldehyde-binding protein 1, RLBP1) encoding proteins of the visual cycle, these lesions manifest as white dot-like puncta. Similar aberrations in photoreceptor cell-attributable SD-OCT reflectivity layers manifest as reticular pseudodrusen (RPD) in short-wavelength fundus autofluorescence and near-infrared fundus autofluorescence fundus images and are linked to age-related macular degeneration a complex disease. Despite differences in the etiologies of retinal diseases presenting as fundus flecks, dots and RPD, underlying degenerative processes in photoreceptor cells are signified in SD-OCT scans by the loss of structural features that would otherwise define healthy photoreceptor cells at these foci.

Defining inclusion criteria and endpoints for clinical trials: a prospective cross-sectional study in CRB1-associated retinal dystrophies

Purpose

To investigate the retinal structure and function in patients with CRB1‐associated retinal dystrophies (RD) and to explore potential clinical endpoints.

Methods

In this prospective cross‐sectional study, 22 patients with genetically confirmed CRB1‐RD (aged 6–74 years), and who had a decimal best‐corrected visual acuity (BCVA) ≥ 0.05 at the last visit, were studied clinically with ETDRS BCVA, corneal topography, spectral‐domain optical coherence tomography (SD‐OCT), fundus autofluorescence, Goldmann visual field (VF), microperimetry, full‐field electroretinography (ERG) and full‐field stimulus testing (FST). Ten patients were from a genetic isolate (GI).

Results

Patients had retinitis pigmentosa (n = 19; GI and non‐GI), cone‐rod dystrophy (n = 2; GI) or macular dystrophy (n = 1; non‐GI). Median age at first symptom onset was 3 years (range 0.8–49). Median decimal BCVA in the better and worse‐seeing eye was 0.18 (range 0.05–0.83) and 0.08 (range light perception‐0.72), respectively. Spectral‐domain optical coherence tomography (SD‐OCT) showed cystoid maculopathy in 8 subjects; inner retinal thickening (n = 20), a well‐preserved (para)foveal outer retina (n = 7) or severe (para)foveal outer retinal atrophy (n = 14). All retinal layers were discernible in 13/21 patients (62%), with mild to moderate laminar disorganization in the others. Nanophthalmos was observed in 8 patients (36%). Full‐field stimulus testing (FST) provided a subjective outcome measure for retinal sensitivity in eyes with (nearly) extinguished ERG amplitudes.

Conclusions

Despite the generally severe course of CRB1‐RDs, symptom onset and central visual function are variable, even at advanced ages. Phenotypes may vary within the same family. Imaging and functional studies in a prospective longitudinal setting should clarify which endpoints may be most appropriate in a clinical trial.

Dorsal-Ventral Differences in Retinal Structure in the Pigmented Royal College of Surgeons Model of Retinal Degeneration

Retinitis pigmentosa is a family of inherited retinal degenerations associated with gradual loss of photoreceptors, that ultimately leads to irreversible vision loss. The Royal College of Surgeon's (RCS) rat carries a recessive mutation affecting mer proto-oncogene tyrosine kinase (merTK), that models autosomal recessive disease. The aim of this study was to understand the glial, microglial, and photoreceptor changes that occur in different retinal locations with advancing disease. Pigmented RCS rats (RCS-p^+/LAV) and age-matched isogenic control rdy (RCS-rdy ⁺p⁺/LAV) rats aged postnatal day 18 to 6 months were evaluated for in vivo retinal structure and function using optical coherence tomography and electroretinography. Retinal tissues were assessed using high resolution immunohistochemistry to evaluate changes in photoreceptors, glia and microglia in the dorsal, and ventral retina. Photoreceptor dysfunction and death occurred from 1 month of age. There was a striking difference in loss of photoreceptors between the dorsal and ventral retina, with a greater number of photoreceptors surviving in the dorsal retina, despite being adjacent a layer of photoreceptor debris within the subretinal space. Loss of photoreceptors in the ventral retina was associated with fragmentation of the outer limiting membrane, extension of glial processes into the subretinal space that was accompanied by possible adhesion and migration of mononuclear phagocytes in the subretinal space. Overall, these findings highlight that breakdown of the outer limiting membrane could play an important role in exacerbating photoreceptor loss in the ventral retina. Our results also highlight the value of using the RCS rat to model sectorial retinitis pigmentosa, a disease known to predominantly effect the inferior retina.

Clinical trial design for neuroprotection in RHO autosomal dominant retinitis pigmentosa; outcome measure considerations

Purpose: To identify structural and functional outcome measures among patients with Rho-positive autosomal dominant Retinitis Pigmentosa (adRP) to aid neuroprotection trial design.Methods: This was a retrospective cohort study of 52 patients with Rho-positive adRP. We measured Goldmann Visual Fields (GVF) constriction in four sectors (nasal, temporal, inferior, superior), and sectoral Ellipsoid Zone (EZ) width degeneration using Spectral Domain Optical Coherence Tomography (OCT) scans. Disease progression trajectories were projected using mixed effects modeling.Results: Superior GVF was most constricted at presentation and had the shallowest trajectory (less steep negative slope); Inferior GVF was less constricted (corrected p < .001) and had a steeper negative slope (corrected p = .019) than superior GVF. Temporal EZ was most stable on OCT with a relatively shallow negative trajectory (corrected p = .011).Conclusions: Patients' superior visual fields presented with more constriction and subsequently had a shallow negative slope suggesting the corresponding inferior retina may be "burned out" at presentation. Targeted therapies for adRP will likely show a greater efficacy signal if delivered to the superior and nasal retina, which may demonstrate more change on OCT and GVF over the course of a neuroprotection trial.Translational Relevance: Mixed effects analysis of sectoral visual field constriction and EZ degeneration in Rho-positive adRP can prove useful in monitoring therapeutic efficacy and identifying targets for local therapies.

The role of multimodal imaging and vision function testing in ABCA4-related retinopathies and their relevance to future therapeutic interventions

The aim of this review article is to describe the specific features of Stargardt disease and ABCA4 retinopathies (ABCA4R) using multimodal imaging and functional testing and to highlight their relevance to potential therapeutic interventions. Standardised measures of tissue loss, tissue function and rate of change over time using formal structured deep phenotyping in Stargardt disease and ABCA4R are key in diagnosis, and prognosis as well as when selecting cohorts for therapeutic intervention. In addition, a meticulous documentation of natural history will be invaluable in the future to compare treated with untreated retinas. Despite the familiarity with the term Stargardt disease, this eponymous classification alone is unhelpful when evaluating ABCA4R, as the ABCA4 gene is associated with a number of phenotypes, and a range of severity. Multimodal imaging, psychophysical and electrophysiologic measurements are necessary in diagnosing and characterising these differing retinopathies. A wide range of retinal dystrophy phenotypes are seen in association with ABCA4 mutations. In this article, these will be referred to as ABCA4R. These different phenotypes and the existence of phenocopies present a significant challenge to the clinician. Careful phenotypic characterisation coupled with the genotype enables the clinician to provide an accurate diagnosis, associated inheritance pattern and information regarding prognosis and management. This is particularly relevant now for recruiting to therapeutic trials, and in the future when therapies become available. The importance of accurate genotype-phenotype correlation studies cannot be overemphasised. This approach together with segregation studies can be vital in the identification of causal mutations when variants in more than one gene are being considered as possible. In this article, we give an overview of the current imaging, psychophysical and electrophysiological investigations, as well as current therapeutic research trials for retinopathies associated with the ABCA4 gene.

Comparing Cone Structure and Function in RHO- and RPGR-Associated Retinitis Pigmentosa

Purpose

To study cone structure and function in patients with retinitis pigmentosa (RP) owing to mutations in rhodopsin (RHO), expressed in rod outer segments, and mutations in the RP-GTPase regulator (RPGR) gene, expressed in the connecting cilium of rods and cones.

Methods

Four eyes of 4 patients with RHO mutations, 5 eyes of 5 patients with RPGR mutations, and 4 eyes of 4 normal subjects were studied. Cone structure was studied with confocal and split-detector adaptive optics scanning laser ophthalmoscopy (AOSLO) and spectral-domain optical coherence tomography. Retinal function was measured using a 543-nm AOSLO-mediated adaptive optics microperimetry (AOMP) stimulus. The ratio of sensitivity to cone density was compared between groups using the Wilcoxon rank-sum test.

Results

AOMP sensitivity/cone density in patients with RPGR mutations was significantly lower than normal (P< 0.001) and lower than patients with RHO mutations (P< 0.015), whereas patients with RHO mutations were similar to normal (P> 0.9).

Conclusions

Retinal sensitivity/cone density was lower in patients with RPGR mutations than normal and lower than patients with RHO mutations, perhaps because cones express RPGR and degenerate primarily, whereas cones in eyes with RHO mutations die secondary to rod degeneration. High-resolution microperimetry can reveal differences in cone degeneration in patients with different forms of RP.

Rod function deficit in retained photoreceptors of patients with class B Rhodopsin mutations

A common inherited retinal disease is caused by mutations in RHO expressed in rod photoreceptors that provide vision in dim ambient light. Approximately half of all RHO mutations result in a Class B phenotype where mutant rods are retained in some retinal regions but show severe degeneration in other regions. We determined the natural history of dysfunction and degeneration of retained rods by serially evaluating patients. Even when followed for more than 20 years, rod function and structure at some retinal locations could remain unchanged. Other locations showed loss of both vision and photoreceptors but the rate of rod vision loss was greater than the rate of photoreceptor degeneration. This unexpected divergence in rates with disease progression implied the development of a rod function deficit beyond loss of cells. The divergence of progression rates was also detectable over a short interval of 2 years near the health-disease transition in the superior retina. A model of structure–function relationship supported the existence of a large rod function deficit which was also most prominent near regions of health-disease transition. Our studies support the realistic therapeutic goal of improved night vision for retinal regions specifically preselected for rod function deficit in patients.

Retinal Dystrophies and the Road to Treatment: Clinical Requirements and Considerations

: Retinal dystrophies (RDs) comprise relatively rare but devastating causes of progressive vision loss. They represent a spectrum of diseases with marked genetic and clinical heterogeneity. Mutations in the same gene may lead to different diagnoses, for example, retinitis pigmentosa or cone dystrophy. Conversely, mutations in different genes may lead to the same phenotype. The age at symptom onset, and the rate and characteristics of peripheral and central vision decline, may vary widely per disease group and even within families. For most RD cases, no effective treatment is currently available. However, preclinical studies and phase I/II/III gene therapy trials are ongoing for several RD subtypes, and recently the first retinal gene therapy has been approved by the US Food and Drug Administration for RPE65-associated RDs: voretigene neparvovec-rzyl (Luxturna). With the rapid advances in gene therapy studies, insight into the phenotypic spectrum and long-term disease course is crucial information for several RD types. The vast clinical heterogeneity presents another important challenge in the evaluation of potential efficacy in future treatment trials, and in establishing treatment candidacy criteria. This perspective describes these challenges, providing detailed clinical descriptions of several forms of RD that are caused by genes of interest for ongoing and future gene or cell-based therapy trials. Several ongoing and future treatment options will be described.

Application of a Deep Machine Learning Model for Automatic Measurement of EZ Width in SD-OCT Images of RP

Purpose

We applied a deep convolutional neural network model for automatic identification of ellipsoid zone (EZ) in spectral domain optical coherence tomography B-scans of retinitis pigmentosa (RP).

Methods

Midline B-scans having visible EZ from 220 patients with RP and 20 normal subjects were manually segmented for inner limiting membrane, inner nuclear layer, EZ, retinal pigment epithelium, and Bruch's membrane. A total of 2.87 million labeled image patches (33 × 33 pixels) extracted from 480 B-scans were used for training a convolutional neural network model implemented in MATLAB. B-scans from a separate group of 80 patients with RP were used for testing the model. A local connected area searching algorithm was developed to process the model output for reconstructing layer boundaries. Correlation and Bland-Altman analyses were conducted to compare EZ width measured by the model to those by manual segmentation.

Results

The accuracy of the trained model to identify inner limiting membrane, inner nuclear layer, EZ, retinal pigment epithelium, and Bruch's membrane patches in the test dataset was 98%, 89%, 91%, 94%, and 96%, respectively. The EZ width measured by the model was highly correlated with that by two graders (r = 0.97; P < 0.0001). Bland-Altman analysis revealed a mean EZ width difference of 0.30 mm (coefficient of repeatability = 0.9 mm) between the model and the graders, comparable to the mean difference of 0.34mm (coefficient of repeatability = 0.8 mm) between two graders.

Conclusions

The results demonstrated the capability of a deep machine learning-based method for automatic identification of EZ in RP, suggesting that the method can be used to quantify structural deficits in RP for detecting disease progression and for evaluating treatment effect.

Translational Relevance

A deep machine learning model has the potential to replace humans for grading spectral domain optical coherence tomography images in RP.

Autosomal Dominant Retinitis Pigmentosa Due to Class B Rhodopsin Mutations: An Objective Outcome for Future Treatment Trials

Gene therapy for adRP due to RHO mutations was recently shown to prevent photoreceptor death in a canine model of Class B disease. Among translational steps to be taken, one is to determine a method to detect efficacy in a human clinical trial. The relatively slow progression of adRP becomes a difficulty for clinical trials requiring an answer to whether there is slowed progression of degeneration in response to therapy. We performed a single-center, retrospective observational study of cross-sectional and longitudinal data. The study was prompted by our identification of a pericentral disease distribution in Class B RHO-adRP. Ultrawide optical coherence tomography (OCT) scans were used. Inferior retinal pericentral defects was an early disease feature. Degeneration further inferior in the retina merged with the pericentral defect, which extended into superior retina. In about 70% of patients, there was an asymmetric island of structure with significantly greater superior than inferior ellipsoid zone (EZ) extent. Serial measures of photoreceptor structure by OCT indicated constriction in superior retinal extent within a two-year interval. We conclude that these results should allow early-phase trials of therapy in RHO-adRP to move forward by inclusion of patients with an asymmetric extent of photoreceptor structure and by monitoring therapeutic effects over two years in the superior retina, a reasonable target for subretinal injection.

The ins and outs of the Arf4-based ciliary membrane-targeting complex

The small GTPase Arf4-based ciliary membrane-targeting complex recognizes specific targeting signals within sensory receptors and regulates their directed movement to primary cilia. Activated Arf4 directly binds the VxPx ciliary-targeting signal (CTS) of the light-sensing receptor rhodopsin. Recent findings revealed that at the trans-Golgi, marked by the small GTPase Rab6, activated Arf4 forms a functional complex with rhodopsin and the Arf guanine nucleotide exchange factor (GEF) GBF1, providing positive feedback that drives further Arf4 activation in ciliary trafficking. Arf4 function is conserved across diverse cell types; however, it appears that not all its aspects are conserved across species, as mouse Arf4 is a natural mutant in the conserved α3 helix, which is essential for its interaction with rhodopsin. Generally, activated Arf4 regulates the assembly of the targeting nexus containing the Arf GAP ASAP1 and the Rab11a-FIP3-Rabin8 dual effector complex, which controls the assembly of the highly conserved Rab11a-Rabin8-Rab8 ciliary-targeting module. It was recently found that this module interacts with the R-SNARE VAMP7, likely in its activated, c-Src-phosphorylated form. Rab11 and Rab8 bind VAMP7 regulatory longin domain (LD), whereas Rabin8 interacts with the SNARE domain, capturing VAMP7 for delivery to the ciliary base and subsequent pairing with the cognate SNAREs syntaxin 3 and SNAP-25. This review will focus on the implications of these novel findings that further illuminate the role of well-ordered Arf and Rab interaction networks in targeting of sensory receptors to primary cilia. Abbreviations: CTS: Ciliary-Targeting Signal; GAP: GTPase Activating Protein; GEF: Guanine Nucleotide Exchange Factor; RTC(s), Rhodopsin Transport Carrier(s); SNARE: Soluble N-ethylmaleimide-sensitive Factor Attachment Protein Receptor; TGN: Trans-Golgi Network.

Clinically Relevant Outcome Measures for the I307N Rhodopsin Mouse: A Model of Inducible Autosomal Dominant Retinitis Pigmentosa

Purpose

The I307N rhodopsin (Rho) mouse is a light-inducible model of autosomal dominant retinitis pigmentosa (adRP) that may be useful in testing therapies. We investigated the time-course of retinal changes of the I307N Rho mouse with spectral-domain optical coherence tomography (SD-OCT).

Methods

SD-OCT was performed up to day 30 after light damage; electroretinography (ERG) was employed to evaluate photoreceptor function. We utilized ImageJ to analyze reflectivity of the retina. We used light and electron microscopy to assess retinal organization. We stained synaptophysin and zonula occludins-1 with immunohistochemistry to determine injury to the plexiform layers and retinal pigment epithelium (RPE). We performed lectin staining to evaluate retinal blood vessels.

Results

Retinal degeneration increased with longer exposures to light. An increase in retinal thickness was detected by SD-OCT on day 1 after light challenge followed by loss of the outer nuclear layer (ONL) by day 8. Degeneration was most severe in the nasal and inferior retina. Hyper-reflectivity on SD-OCT developed as early as 1 day after light exposure. Disorganization of the ONL, condensation of photoreceptor chromatin, disruption of the outer limiting membrane, and disarray of outer segments were associated with the hyper-reflectivity. Retraction of the outer plexiform synapses and resorption of the subretinal detachment contributed to retinal thinning. The RPE remained intact, whereas atrophied major retinal vessels were evident after light damage.

Conclusions

Our time-course analysis of retinal degeneration in the I307N Rho mouse with SD-OCT and other outcome measures should enable the use of the mouse model in preclinical efficacy studies and mechanistic studies.

RDH12 Mutations Cause a Severe Retinal Degeneration With Relatively Spared Rod Function

Purpose

To describe the retinal phenotype of pediatric patients with mutations in the retinol dehydrogenase 12 (RDH12) gene.

Methods

Twenty-one patients from 14 families (ages 2-17 years) with RDH12-associated inherited retinal degeneration (RDH12-IRD) underwent a complete ophthalmic exam and imaging with spectral domain optical coherence tomography (SD-OCT) and near infrared and short-wavelength fundus autofluorescence. Visual field extent was measured with Goldmann kinetic perimetry, visual thresholds with dark-adapted static perimetry or with dark-adapted chromatic full-field stimulus testing (FST) and transient pupillometry.

Results

Visual acuity ranged from 20/40 to light perception. There was parafoveal depigmentation or atrophic maculopathies accompanied by midperipheral intraretinal pigment migration. SD-OCT revealed foveal thinning in all patients and detectable but thinned outer nuclear layer (ONL) at greater eccentricities from the fovea. Photoreceptor outer segment (POS) signals were only detectable in small pockets within the central retina. Measurable kinetic visual fields were limited to small (<5-10°) central islands of vision. Electroretinograms were reported as undetectable or severely reduced in amplitude. FST sensitivities to a 467 nm stimulus were rod-mediated and reduced on average by ∼2.5 log units. A thinned central ONL colocalized with severely reduced to nondetectable cone-mediated sensitivities. Pupillometry confirmed the psychophysically measured abnormalities.

Conclusions

RDH12-IRD causes an early-onset, retina-wide disease with particularly severe central retinal abnormalities associated with relatively less severe rod photoreceptor dysfunction, a pattern consistent with an early-onset cone-rod dystrophy. Severely abnormal POS but detectable ONL in the pericentral and peripapillary retina suggest these regions may become targets for gene therapy.

Course of loss of photoreceptor function and progressive Müller cell gliosis in rhodopsin P347L transgenic rabbits

Long living animal models of retinitis pigmentosa (RP) can provide important information on the retinal changes that occur at the late stages of photoreceptor degeneration. The rhodopsin Pro347Leu transgenic rabbit (P347L Tg) is a model of RP, and it has been used to analyze the functional and morphological changes in the retina following the degeneration of the photoreceptors. They have also been used to test newly-developed therapies to treat eyes with photoreceptor degeneration. However, assessments of the retinal changes in P347L Tg rabbits older than 1-year have not been reported even though the data are important for research on developing new therapies to restore vision at the end stages of RP. The purpose of this study was to determine the time course of the loss of photoreceptor function and the changes in the morphology of the retina of P347L Tg rabbits. The experiments were performed on 26 older P347L Tg rabbits. The results showed that the amplitudes of the ERGs of the P347L Tg rabbits gradually decreased and reached <10 μV between 30- and 54-months-of-age. Histological analysis at these later stages showed a loss of the photoreceptor layer, and OCT analysis showed absence of the layering of the retina. However, the thickness between the inner limiting membrane and the outer plexiform layer was about 1.7 times thicker than the corresponding thickness of WT rabbits in the OCT images. This thickening was caused by a marked gliosis of the entire retina which was confirmed by light and transmission electron microscopy. In addition, immunohistochemical analysis showed there was excessive staining of the glial fibrillary acid protein in the older P347L Tg rabbits although the rod ON bipolar cells and horizontal cells were still present in the inner nuclear layer. Our results indicate that the P347L Tg rabbit progressed to complete photoreceptor loss within 30- and 54-months-of-age and severe gliosis altered the morphology of the retina.

Rhodopsin gene mutation analysis in Iranian patients with autosomal dominant retinitis pigmentosa

PURPOSE

Retinitis pigmentosa (RP) is the most common hereditary retinal degeneration and an important cause of visual disability worldwide. Rhodopsin gene is one of the most important genes implicated in autosomal dominant RP (ADRP). In this study, we investigated rhodopsin gene mutations in Iranian patients with ADRP.

METHODS

Twenty-one patients from 21 unrelated families with a total of 51 affected members were enrolled in this study. After complete history taking, ophthalmic examination and genetic counseling, peripheral blood samples were obtained. Following genomic DNA extraction, all five exons and intron-exon boundaries of RHO gene were sequenced using Sanger method. Interpretation of detected variants was carried out using appropriate databases and bioinformatic tools. Novel variants were screened in 150 unrelated healthy subjects.

RESULTS

Results of direct sequencing revealed that five of 21 patients (23.8%) had mutation in the rhodopsin gene. Two of them had previously identified p.P347L mutation, and three had novel variants including p.L95P, p.R177K and p.N310K. None of these novel variants were detected in healthy controls. The p.L95P variant was associated with predominantly inferior retinal involvement.

CONCLUSIONS

Our study showed that mutations of the rhodopsin gene are relatively frequent in Iranian patients with ADRP and could be considered in further researches in the future. The novel p.L95P variant may be associated with a specific pattern of retinal degeneration in this population.

Significant Relationship of Visual Field Sensitivity in Central 10° to Thickness of Retinal Layers in Retinitis Pigmentosa

Purpose

To determine the relationship between the sensitivity of the retina in the central 10° and the thickness of the retinal layers in patients with retinitis pigmentosa (RP).

Methods

Fifty-two RP patients were studied. All of the patients had been examined by the Humphrey Field Analyzer 10-2 program (HFA10-2) and spectral-domain optical coherence tomography (SD-OCT). The thicknesses of the photoreceptor outer segment (OS), outer nuclear layer (ONL), inner nuclear layer (INL), and the retinal nerve fiber layer (RNFL) were measured at 1°, 3°, 5°, 7°, and 9° from the fovea. The same measurements were made on the SD-OCT images of 40 healthy subjects and used as controls. The relationships between the retinal sensitivities and retinal layer thicknesses were determined.

Results

The thicknesses of the OS and ONL and their product were significantly and positively correlated with the retinal sensitivities. The thickness of the INL was significantly and negatively correlated with the sensitivity. The strongest correlation with the sensitivity was with the OS thickness (marginal R2 [mR2] = 0.525, P < 0.001), followed by the product of the OS and ONL thicknesses (mR2 = 0.420, P < 0.001), ONL thickness (mR2 = 0.416, P < 0.001), and the INL thickness (mR2 = 0.014, P = 0.044). The thickness of the RNFL was not correlated with the sensitivity (mR2 = 0.005, P = 0.331).

Conclusions

In contrast to previous reports, the thickness of the OS reflected the retinal sensitivity better than the product of OS and ONL.

FREQUENT SUBCLINICAL MACULAR CHANGES IN COMBINED BRAF/MEK INHIBITION WITH HIGH-DOSE HYDROXYCHLOROQUINE AS TREATMENT FOR ADVANCED METASTATIC BRAF MUTANT MELANOMA: Preliminary Results From a Phase I/II Clinical Treatment Trial

PURPOSE

To assess the potential ocular toxicity of a combined BRAF inhibition (BRAFi) + MEK inhibition (MEKi) + hydroxychloroquine (HCQ) regime used to treat metastatic BRAF mutant melanoma.

METHODS

Patients with stage IV metastatic melanoma and BRAF V600E mutations (n = 11, 31-68 years of age) were included. Treatment was with oral dabrafenib, 150 mg bid, trametinib, 2 mg/day, and HCQ, 400 mg to 600 mg bid. An ophthalmic examination, spectral domain optical coherence tomography, near-infrared and short-wavelength fundus autofluorescence, and static perimetry were performed at baseline, 1 month, and q/6 months after treatment.

RESULTS

There were no clinically significant ocular events; there was no ocular inflammation. The only medication-related change was a separation of the photoreceptor outer segment tip from the apical retinal pigment epithelium that could be traced from the fovea to the perifoveal retina noted in 9/11 (82%) of the patients. There were no changes in retinal pigment epithelium melanization or lipofuscin content by near-infrared fundus autofluorescence and short-wavelength fundus autofluorescence, respectively. There were no inner retinal or outer nuclear layer changes. Visual acuities and sensitivities were unchanged.

CONCLUSION

BRAFi (trametinib) + MEKi (dabrafenib) + HCQ causes very frequent, subclinical separation of the photoreceptor outer segment from the apical retinal pigment epithelium without inner retinal changes or signs of inflammation. The changes suggest interference with the maintenance of the outer retinal barrier and/or phagocytic/pump functions of the retinal pigment epithelium by effective MEK inhibition.

Imaging retinal melanin: a review of current technologies

The retinal pigment epithelium (RPE) is essential to the health of the retina and the proper functioning of the photoreceptors. The RPE is rich in melanosomes, which contain the pigment melanin. Changes in RPE pigmentation are seen with normal aging and in diseases such as albinism and age-related macular degeneration. However, most techniques used to this day to detect and quantify ocular melanin are performed ex vivo and are destructive to the tissue. There is a need for in vivo imaging of melanin both at the clinical and pre-clinical level to study how pigmentation changes can inform disease progression. In this manuscript, we review in vivo imaging techniques such as fundus photography, fundus reflectometry, near-infrared autofluorescence imaging, photoacoustic imaging, and functional optical coherence tomography that specifically detect melanin in the retina. These methods use different contrast mechanisms to detect melanin and provide images with different resolutions and field-of-views, making them complementary to each other.

Ganglion cell-inner plexiform layer and retinal nerve fibre layer changes within the macula in retinitis pigmentosa: a spectral domain optical coherence tomography study

PURPOSE

To investigate how macular ganglion cell-inner plexiform layer (GCIPL) and retinal nerve fibre layer (RNFL) thicknesses within the macula change with retinitis pigmentosa (RP) severity.

METHODS

Spectral domain optical coherence tomography (SD-OCT) was used to examine 177 patients with RP and 177 normal controls. An optical coherence tomography (OCT) line scan was used to grade RP severity. Retinitis pigmentosa (RP) was categorized as more advanced if there was no identifiable inner segment ellipsoid (ISe) band (NISE) and as less advanced if an ISe band could be identified and peripheral loss of ISe was apparent (IISE). Ganglion cell-inner plexiform layer (GCIPL) and RNFL thicknesses were manually measured on OCT images and analysed. Pearson's correlation analyses were used to examine correlations between GCIPL thickness, RNFL thickness, visual acuity (VA) and visual field extent in patients and controls.

RESULTS

Ganglion cell-inner plexiform layer (GCIPL) was significantly thicker in IISE than in control eyes (p < 0.001), but significantly thinner in NISE than in IISE eyes (p < 0.001) in both horizontal and vertical OCT scans. Retinal nerve fibre layer (RNFL) was significantly thicker in eyes with IISE and NISE than in control eyes in both horizontal and vertical meridians (all p < 0.001). Ganglion cell-inner plexiform layer (GCIPL) thickness showed a weak positive correlation with vision, and RNFL thickness showed a weak negative correlation with vision and visual field extent.

CONCLUSION

Based on these results, the inner retina, including the GCIPL and RNFL, maintains its gross integrity longer than the photoreceptor layer in RP. Additionally, thickening of the inner retina may have some functional implications in patients with RP.

EYS Mutations Causing Autosomal Recessive Retinitis Pigmentosa: Changes of Retinal Structure and Function with Disease Progression

Mutations in the EYS (eyes shut homolog) gene are a common cause of autosomal recessive (ar) retinitis pigmentosa (RP). Without a mammalian model of human EYS disease, there is limited understanding of details of disease expression and rates of progression of the retinal degeneration. We studied clinically and with chromatic static perimetry, spectral-domain optical coherence tomography (OCT), and en face autofluoresence imaging, a cohort of 15 patients (ages 12–51 at first visit), some of whom had longitudinal data of function and structure. Rod sensitivity was able to be measured by chromatic perimetry in most patients at their earliest visits and some patients retained patchy rod function into the fifth decade of life. As expected from RP, cone sensitivity persisted after rod function was no longer measurable. The photoreceptor nuclear layer of the central retina was abnormal except at the fovea in most patients at first visit. Perifoveal disease measured over a period of years indicated that photoreceptor structural loss was followed by dysmorphology of the inner retina and loss of retinal pigment epithelial integrity. Although there could be variability in severity, preliminary analyses of the rates of vision loss suggested that EYS is a more rapidly progressive disease than other ciliopathies causing arRP, such as USH2A and MAK.

Quantifying Fundus Autofluorescence in Patients With Retinitis Pigmentosa

Purpose

Using quantitative fundus autofluorescence (qAF), we analyzed short-wavelength autofluorescent (SW-AF) rings in RP.

Methods

Short-wavelength autofluorescent images (486 nm excitation) of 40 patients with RP (69 eyes) were acquired with a confocal scanning laser ophthalmoscope equipped with an internal fluorescent reference. Mean qAF was measured in eight preset segments (qAF₈) and in region of interest (ROI)-qAF (200–700 μm) within and external to the borders of the rings at superior, temporal, and inferior sites relative to the ring. For both groups, qAF in patients with RP was compared to age-similar and race/ethnicity-matched healthy eyes at equivalent retinal locations.

Results

In 71% of eyes of RP patients, qAF₈ acquired internal to the inner border of the ring, was within the 95% confidence interval (CI) for healthy eyes, while in the remaining RP eyes qAF₈ was either higher or lower than the CI. Measured external to the ring, qAF₈ values were within the CI in 47% of RP eyes with the other eyes being higher or lower. In 28% of sites measured by ROI-qAF within the SW-AF ring, values were above the 95% CI of healthy controls. Region of interest-qAF measured just external to the ring was within the CI of healthy eyes in 74% of locations. The average local elevation in qAF within the ring was approximately 15%. In SD-OCT scans, photoreceptor-attributable reflectivity bands were thinned within and external to the ring.

Conclusions

Increased fluorophore production may be a factor in the formation of the SW-AF rings in RP.

Quantitative Analysis of Retinal Structure Using Spectral-Domain Optical Coherence Tomography in RPGR-Associated Retinopathy

Purpose

To quantify retinal structure and progression using spectral-domain optical coherence tomography (SDOCT) in patients with retinitis pigmentosa (RP) associated with retinitis pigmentosa GTPase regulator gene (RPGR) mutations.

Design

Retrospective observational case series.

Methods

Setting: Moorfields Eye Hospital, London, United Kingdom. Subjects: Both eyes of 32 patients. SDOCT follow-up period of >1 year (3.1 ± 1.4 years). Main Outcome Measures: Ellipsoid zone (EZ) width (EZW) and outer nuclear layer (ONL) and inner retinal layer (IRL) thickness measurements. Progression rates, interocular symmetry, and association with age and genotype were investigated.

Results

Significant differences were observed between baseline and final measurements of EZW and ONL thickness, but not for IRL thickness. Baseline and final EZWs were 2438 ± 1646 μm and 1901 ± 1423 μm for right eyes (P < .0001); 2420 ± 1758 μm and 1922 ± 1482 μm for left eyes (P < .0001). EZW constriction rates were 176.6 ± 130.1 μm/year and 173.1 ± 146.8 μm/year for right and left eyes. ONL thinning rates were 2.58 ± 2.85 μm/year and 2.52 ± 3.54 μm/year for right and left eyes. Interocular differences in EZW and ONL progression were not significant (P = .8609 and P = .6735, respectively). Strong correlations were found between EZW constriction rates of right and left eyes (r_s = 0.627, P = .0002) and between EZW constriction and baseline EZW (r_s = 0.714, P < .0001). There was moderate negative correlation between EZW constriction and age (r_s = −0.532, P < .0001). Correlation between ONL thinning and age was not significant, as were differences between EZW and ONL progression rates with respect to genotype.

Conclusions

This study provides SDOCT progression rates for RPGR-associated RP. There is overall interocular symmetry with implications for future treatment trials where 1 eye could serve as a control.

Postretinal Structure and Function in Severe Congenital Photoreceptor Blindness Caused by Mutations in the GUCY2D Gene

Purpose

To examine how severe congenital blindness resulting from mutations of the GUCY2D gene alters brain structure and function, and to relate these findings to the notable preservation of retinal architecture in this form of Leber congenital amaurosis (LCA).

Methods

Six GUCY2D-LCA patients (ages 20–46) were studied with optical coherence tomography of the retina and multimodal magnetic resonance imaging (MRI) of the brain. Measurements from this group were compared to those obtained from populations of normally sighted controls and people with congenital blindness of a variety of causes.

Results

Patients with GUCY2D-LCA had preservation of the photoreceptors, ganglion cells, and nerve fiber layer. Despite this, visual function in these patients ranged from 20/160 acuity to no light perception, and functional MRI responses to light stimulation were attenuated and restricted. This severe visual impairment was reflected in substantial thickening of the gray matter layer of area V1, accompanied by an alteration of resting-state correlations within the occipital lobe, similar to a comparison group of congenitally blind people with structural damage to the retina. In contrast to the comparison blind population, however, the GUCY2D-LCA group had preservation of the size of the optic chiasm, and the fractional anisotropy of the optic radiations as measured with diffusion tensor imaging was also normal.

Conclusions

These results identify dissociable effects of blindness upon the visual pathway. Further, the relatively intact postgeniculate white matter pathway in GUCY2D-LCA is encouraging for the prospect of recovery of visual function with gene augmentation therapy.

Variegated yet non-random rod and cone photoreceptor disease patterns in RPGR-ORF15-associated retinal degeneration

Mutations in the ORF15 exon of the RPGR gene cause a common form of X-linked retinitis pigmentosa, which often results in severe loss of vision. In dogs and mice, gene augmentation therapy has been shown to arrest the progressive degeneration of rod and cone photoreceptors. However, the distribution of potentially treatable photoreceptors across the human retinas and the rate of degeneration are not known. Here, we have defined structural and functional features of the disease in 70 individuals with ORF15 mutations. We also correlated the features observed in patients with those of three Rpgr-mutant (Rpgr-ko, Rd9, and Rpgr-cko) mice. In patients, there was pronounced macular disease. Across the retina, rod and cone dysfunction showed a range of patterns and a spectrum of severity between individuals, but a high symmetry was observed between eyes of each individual. Genotype was not related to disease expression. In the Rpgr-ko mice, there were intra-retinal differences in rhodopsin and cone opsin trafficking. In Rd9 and Rpgr-cko mice, retinal degeneration showed inter-ocular symmetry. Longitudinal results in patients revealed localized rod and cone dysfunction with progression rates of 0.8 to 1.3 log per decade in sensitivity loss. Relatively retained rod and cone photoreceptors in mid- and far-peripheral temporal-inferior and nasal-inferior visual field regions should be good targets for future localized gene therapies in patients.

Natural History of the Central Structural Abnormalities in Choroideremia: A Prospective Cross-Sectional Study

PURPOSE

To describe in detail the central retinal structure of a large group of patients with choroideremia (CHM).

DESIGN

A prospective, cross-sectional, descriptive study.

PARTICIPANTS

Patients (n = 97, age 6-71 years) with CHM and subjects with normal vision (n = 44; ages 10-50 years) were included.

METHODS

Subjects were examined with spectral-domain optical coherence tomography (SD OCT) and near-infrared reflectance imaging. Visual acuity (VA) was measured during their encounter or obtained from recent ophthalmic examinations. Visual thresholds were measured in a subset of patients (n = 24) with automated static perimetry within the central regions (±15°) examined with SD OCT.

MAIN OUTCOME MEASURES

Visual acuity and visual thresholds; total nuclear layer, inner nuclear layer (INL), and outer nuclear layer (ONL) thicknesses; and horizontal extent of the ONL and the photoreceptor outer segment (POS) interdigitation zone (IZ).

RESULTS

Earliest abnormalities in regions with normally appearing retinal pigment epithelium (RPE) were the loss of the POS and ellipsoid zone associated with rod dysfunction. Transition zones (TZs) from relatively preserved retina to severe ONL thinning and inner retinal thickening moved centripetally with age. Most patients (88%) retained VAs better than 20/40 until their fifth decade of life. The VA decline coincided with migration of the TZ near the foveal center. There were outer retinal tubulations in degenerated, nonatrophic retina in the majority (69%) of patients. In general, RPE abnormalities paralleled photoreceptor degeneration, although there were regions with detectable but abnormally thin ONL co-localizing with severe RPE depigmentation and choroidal thinning.

CONCLUSIONS

Abnormalities of the POS and rod dysfunction are the earliest central abnormalities observed in CHM. Foveal function is relatively preserved until the fifth decade of life. Migration of the TZs to the foveal center with foveal thinning and structural disorganization heralded central VA loss. The relationships established may help outline the eligibility criteria and outcome measures for clinical trials for CHM.

Complexity of the Class B Phenotype in Autosomal Dominant Retinitis Pigmentosa Due to Rhodopsin Mutations

Purpose

Previously, patients with RHO mutations and a class A phenotype were found to have severe early-onset loss of rod function, whereas patients with a class B phenotype retained rod function at least in certain retinal regions. Here class B patients were studied at different disease stages to understand the topographic details of the phenotype in preparation for therapies of this regionalized retinopathy.

Methods

A cohort of patients with RHO mutations and class B phenotype (n = 28; ages 10–80 years) were studied with rod and cone perimetry and optical coherence tomography (OCT).

Results

At least three components of the phenotype were identified in these cross-sectional studies. Patients could have hemifield dysfunction, pericentral loss of function, or a diffuse rod sensitivity loss across the visual field. Combinations of these different patterns were also found. Colocalized photoreceptor layer thicknesses were in agreement with the psychophysical results.

Conclusions

These disorders with regional retinal variation of severity require pre-evaluations before enrollment into clinical trials to seek answers to questions about where in the retina would be appropriate to deliver focal treatments, and, for retina-wide treatment strategies, where in the retina should be monitored for therapeutic efficacy (or safety).

cGMP production of patient-specific iPSCs and photoreceptor precursor cells to treat retinal degenerative blindness

Immunologically-matched, induced pluripotent stem cell (iPSC)-derived photoreceptor precursor cells have the potential to restore vision to patients with retinal degenerative diseases like retinitis pigmentosa. The purpose of this study was to develop clinically-compatible methods for manufacturing photoreceptor precursor cells from adult skin in a non-profit cGMP environment. Biopsies were obtained from 35 adult patients with inherited retinal degeneration and fibroblast lines were established under ISO class 5 cGMP conditions. Patient-specific iPSCs were then generated, clonally expanded and validated. Post-mitotic photoreceptor precursor cells were generated using a stepwise cGMP-compliant 3D differentiation protocol. The recapitulation of the enhanced S-cone phenotype in retinal organoids generated from a patient with NR2E3 mutations demonstrated the fidelity of these protocols. Transplantation into immune compromised animals revealed no evidence of abnormal proliferation or tumor formation. These studies will enable clinical trials to test the safety and efficiency of patient-specific photoreceptor cell replacement in humans.

Cobalamin C Deficiency Shows a Rapidly Progressing Maculopathy With Severe Photoreceptor and Ganglion Cell Loss

PURPOSE

To describe in detail the retinal structure and function of a group of patients with cobalamin C (cblC) disease.

METHODS

Patients (n = 11, age 4 months to 15 years) with cblC disease (9/11, early onset) diagnosed by newborn screening underwent complete ophthalmic examinations, fundus photography, near-infrared reflectance imaging, and spectral-domain optical coherence tomography (SD-OCT). Electroretinograms (ERGs) were performed in a subset of patients.

RESULTS

Patients carried homozygous or compound heterozygote mutations in the methylmalonic aciduria and homocystinuria type C (MMACHC) gene. Late-onset patients had a normal exam. All early-onset patients showed a maculopathy; older subjects had a retina-wide degeneration (n = 4; >7 years of age). In general, retinal changes were first observed before 1 year of age and progressed within months to a well-established maculopathy. Pseudocolobomas were documented in three patients. Measurable visual acuities ranged from 20/200 to 20/540. Nystagmus was present in 8/11 patients; 5/6 patients had normal ERGs; 1/6 had reduced rod-mediated responses. Spectral-domain OCT showed macular thinning, with severe ganglion cell layer (GCL) and outer nuclear layer (ONL) loss. Inner retinal thickening was observed in areas of total GCL/ONL loss. A normal lamination pattern in the peripapillary nasal retina was often seen despite severe central and/or retina-wide disease.

CONCLUSIONS

Patients with early-onset cblC and MMACHC mutations showed an early-onset, unusually fast-progressing maculopathy with severe central ONL and GCL loss. An abnormally thickened inner retina supports a remodeling response to both photoreceptor and ganglion cell degeneration and/or an interference with normal development in early-onset cblC.

SPATA7: Evolving phenotype from cone-rod dystrophy to retinitis pigmentosa

BACKGROUND

SPATA7 mutations have been associated with different autosomal recessive retinal degeneration phenotypes. Long-term follow-up has not been described in detail.

MATERIALS AND METHODS

A Hispanic patient with SPATA7 mutations was evaluated serially over a 12-year period with kinetic and static chromatic perimetry, optical coherence tomography (OCT), and fundus autofluorescence (AF) imaging. Electroretinography (ERG) was performed at the initial visit.

RESULTS

The patient was homozygous for a mutation in SPATA7 (p.V458fs). At age 9, the ERG showed an abnormally reduced but preserved rod b-wave and no detectable cone signals. There were two islands of vision: a midperipheral island with greater cone than rod dysfunction and a central island with normal cone but no rod function. Serial measures of rod and cone vision and co-localized retinal structure showed that the midperipheral island slowly became undetectable. By age 21, only the central island and its cone function remained, but it had become more abnormal in structure and function.

CONCLUSION

The disease resulting from SPATA7 mutations in this patient initially presented as a cone-rod dystrophy (CRD), but changed over time into a phenotype more reminiscent of late-stage retinitis pigmentosa (RP). The differential diagnosis for both CRD and RP should include this rare molecular cause of autosomal retinal degeneration. An evolving phenotype complicates not only clinical diagnosis and patient counselling but also future strategies aimed at treating specific retinal regions.

Molecular Heterogeneity Within the Clinical Diagnosis of Pericentral Retinal Degeneration

PURPOSE

To characterize in detail the phenotype and genotype of patients with pericentral retinal degeneration (PRD).

METHODS

Patients were screened for an annular ring scotoma ranging from 3° to 40° (n = 28, ages 24-71) with kinetic perimetry. All patients had pigmentary retinopathy in the region of the dysfunction. Further studies included cross-sectional and en face imaging, static chromatic perimetry, and electroretinography. Molecular screening was performed.

RESULTS

Genotypes of 14 of 28 PRD patients were identified: There were mutations in eight different genes previously associated with autosomal dominant or autosomal recessive RDs. Kinetic fields monitored in some patients over years to more than a decade could be stable or show increased extent of the scotoma. Electroretinograms were recordable but with different severities of dysfunction. Patterns of photoreceptor outer nuclear layer (ONL) loss corresponded to the distribution of visual dysfunction. Outer nuclear layer thickness topography and en face imaging indicated that the greatest disease expression was in the area of known highest rod photoreceptor density.

CONCLUSIONS

Molecular heterogeneity was a feature of the PRD phenotype. Many of the molecular causes were also associated with other phenotypes, such as maculopathies, typical retinitis pigmentosa (RP) and cone-rod dystrophy. The pericentral pattern of retinal degeneration is thus confirmed to be an uncommon phenotype of many different genotypes rather than a distinct disease entity.

Autofluorescence imaging with near-infrared excitation:normalization by reflectance to reduce signal from choroidal fluorophores

PURPOSE

We previously developed reduced-illuminance autofluorescence imaging (RAFI) methods involving near-infrared (NIR) excitation to image melanin-based fluorophores and short-wavelength (SW) excitation to image lipofuscin-based flurophores. Here, we propose to normalize NIR-RAFI in order to increase the relative contribution of retinal pigment epithelium (RPE) fluorophores.

METHODS

Retinal imaging was performed with a standard protocol holding system parameters invariant in healthy subjects and in patients. Normalized NIR-RAFI was derived by dividing NIR-RAFI signal by NIR reflectance point-by-point after image registration.

RESULTS

Regions of RPE atrophy in Stargardt disease, AMD, retinitis pigmentosa, choroideremia, and Leber congenital amaurosis as defined by low signal on SW-RAFI could correspond to a wide range of signal on NIR-RAFI depending on the contribution from the choroidal component. Retinal pigment epithelium atrophy tended to always correspond to high signal on NIR reflectance. Normalizing NIR-RAFI reduced the choroidal component of the signal in regions of atrophy. Quantitative evaluation of RPE atrophy area showed no significant differences between SW-RAFI and normalized NIR-RAFI.

CONCLUSIONS

Imaging of RPE atrophy using lipofuscin-based AF imaging has become the gold standard. However, this technique involves bright SW lights that are uncomfortable and may accelerate the rate of disease progression in vulnerable retinas. The NIR-RAFI method developed here is a melanin-based alternative that is not absorbed by opsins and bisretinoid moieties, and is comfortable to view. Further development of this method may result in a nonmydriatic and comfortable imaging method to quantify RPE atrophy extent and its expansion rate.

Retinal histopathology in eyes from patients with autosomal dominant retinitis pigmentosa caused by rhodopsin mutations

PURPOSE

To evaluate the histopathology in donor eyes from patients with autosomal dominant retinitis pigmentosa (ADRP) caused by p.P23H, p.P347T and p.P347L rhodopsin ( RHO ) gene mutations.

METHODS

Eyes from a 72-year-old male (donor 1), an 83-year-old female (donor 2), an 80-year-old female (donor 3), and three age-similar normal eyes were examined macroscopically, by scanning laser ophthalmoscopy and optical coherence tomography imaging. Perifoveal and peripheral pieces were processed for microscopy and immunocytochemistry with markers for photoreceptor cells.

RESULTS

DNA analysis revealed RHO mutations c.68C>A (p.P23H) in donor 1, c.1040C>T (p.P347L) in donor 2 and c.1039C>A (p.P347T) in donor 3. Histology of the ADRP eyes showed retinas with little evidence of stratified nuclear layers in the periphery and a prominent inner nuclear layer present in the perifoveal region in the p.P23H and p.P347T eyes, while it was severely atrophic in the p.P347L eye. The p.P23H and p.P347T mutations cause a profound loss of rods in both the periphery and perifovea, while the p.P347L mutation displays near complete absence of rods in both regions. All three rhodopsin mutations caused a profound loss of cones in the periphery. The p.P23H and p.P347T mutations led to the presence of highly disorganized cones in the perifovea. However, the p.P347L mutation led to near complete absence of cones also in the perifovea.

CONCLUSIONS

Our results support clinical findings indicating that mutations affecting residue P347 develop more severe phenotypes than those affecting P23. Furthermore, our results indicate a more severe phenotype in the p.P347L retina as compared to the p.P347T retina.

Genotypic and phenotypic characterization of P23H line 1 rat model

Rod-cone dystrophy, also known as retinitis pigmentosa (RP), is the most common inherited degenerative photoreceptor disease, for which no therapy is currently available. The P23H rat is one of the most commonly used autosomal dominant RP models. It has been created by incorporation of a mutated mouse rhodopsin (Rho) transgene in the wild-type (WT) Sprague Dawley rat. Detailed genetic characterization of this transgenic animal has however never been fully reported. Here we filled this knowledge gap on P23H Line 1 rat (P23H-1) and provide additional phenotypic information applying non-invasive and state-of-the-art in vivo techniques that are relevant for preclinical therapeutic evaluations. Transgene sequence was analyzed by Sanger sequencing. Using quantitative PCR, transgene copy number was calculated and its expression measured in retinal tissue. Full field electroretinography (ERG) and spectral domain optical coherence tomography (SD-OCT) were performed at 1-, 2-, 3- and 6-months of age. Sanger sequencing revealed that P23H-1 rat carries the mutated mouse genomic Rho sequence from the promoter to the 3’ UTR. Transgene copy numbers were estimated at 9 and 18 copies in the hemizygous and homozygous rats respectively. In 1-month-old hemizygous P23H-1 rats, transgene expression represented 43% of all Rho expressed alleles. ERG showed a progressive rod-cone dysfunction peaking at 6 months-of-age. SD-OCT confirmed a progressive thinning of the photoreceptor cell layer leading to the disappearance of the outer retina by 6 months with additional morphological changes in the inner retinal cell layers in hemizygous P23H-1 rats. These results provide precise genotypic information of the P23H-1 rat with additional phenotypic characterization that will serve basis for therapeutic interventions, especially for those aiming at gene editing.

Correlation of outer nuclear layer thickness with cone density values in patients with retinitis pigmentosa and healthy subjects

PURPOSE

We studied the correlation between outer nuclear layer (ONL) thickness and cone density in normal eyes and eyes with retinitis pigmentosa (RP).

METHODS

Spectral-domain optical coherence tomography (SD-OCT) scans were acquired using a displaced pupil entry position of the scanning beam to distinguish Henle's fiber layer from the ONL in 20 normal eyes (10 subjects) and 12 eyes with RP (7 patients). Cone photoreceptors were imaged using adaptive optics scanning laser ophthalmoscopy. The ONL thickness and cone density were measured at 0.5° intervals along the horizontal meridian through the fovea nasally and temporally. The ONL thickness and cone density were correlated using Spearman's rank correlation coefficient r.

RESULTS

Cone densities averaged over the central 6° were lower in eyes with RP than normal, but showed high variability in both groups. The ONL thickness and cone density were significantly correlated when all retinal eccentricities were combined (r = 0.74); the correlation for regions within 0.5° to 1.5° eccentricity was stronger (r = 0.67) than between 1.5° and 3.0° eccentricity (r = 0.23). Although cone densities were lower between 0.5° and 1.5° in eyes with RP, ONL thickness measures at identical retinal locations were similar in the two groups (P = 0.31), and interindividual variation was high for ONL and cone density measures. Although ONL thickness and retinal eccentricity were important predictors of cone density, eccentricity was over 3 times more important.

CONCLUSIONS

The ONL thickness and cone density were correlated in normal eyes and eyes with RP, but both were strongly correlated with retinal eccentricity, precluding estimation of cone density from ONL thickness. (ClinicalTrials.gov number, NCT00254605.).

Antibody neutralization poses a barrier to intravitreal adeno-associated viral vector gene delivery to non-human primates

Gene delivery vectors based on adeno-associated viruses (AAV) have exhibited promise in both preclinical disease models and human clinical trials for numerous disease targets, including the retinal degenerative disorders Leber's congenital amaurosis and choroideremia. One general challenge for AAV is that preexisting immunity, as well as subsequent development of immunity following vector administration, can severely inhibit systemic AAV vector gene delivery. However, the role of neutralizing antibodies (NABs) in AAV transduction of tissues considered to be immune privileged, such as the eye, is unclear in large animals. Intravitreal AAV administration allows for broad retinal delivery, but is more susceptible to interactions with the immune system than subretinal administration. To assess the effects of systemic anti-AAV antibody levels on intravitreal gene delivery, we quantified the anti-AAV antibodies present in sera from non-human primates before and after intravitreal injections with various AAV capsids. Analysis showed that intravitreal administration resulted in an increase in anti-AAV antibodies regardless of the capsid serotype, transgene or dosage of virus injected. For monkeys injected with wild-type AAV2 and/or an AAV2 mutant, the variable that most significantly affected the production of anti-AAV2 antibodies was the amount of virus delivered. In addition, post-injection antibody titers were highest against the serotype administered, but the antibodies were also cross-reactive against other AAV serotypes. Furthermore, NAB levels in serum correlated with those in vitreal fluid, demonstrating both that this route of administration exposes AAV capsid epitopes to the adaptive immune system and that serum measurements are predictive of vitreous fluid NAB titers. Moreover, the presence of preexisting NAB titers in the serum of monkeys correlated strongly (R=0.76) with weak, decaying or no transgene expression following intravitreal administration of AAV. Investigating anti-AAV antibody development will aid in understanding the interactions between gene therapy vectors and the immune system during ocular administration and can form a basis for future clinical studies applying intravitreal gene delivery.