Chromatic Full-Field Stimulus Threshold and Pupillography as Functional Markers for Late-Stage, Early-Onset Retinitis Pigmentosa Caused by CRB1 Mutations

Influencing Factors on Pupillary Light Responses as a Biomarker for Local Retinal Function in a Large Normative Cohort

Purpose

Investigating influencing factors on the pupillary light response (PLR) as a biomarker for local retinal function by providing epidemiological data of a large normative collective and to establish a normative database for the evaluation of chromatic pupil campimetry (CPC).

Methods

Demographic and ophthalmologic characteristics were captured and PLR parameters of 150 healthy participants (94 women) aged 18 to 79 years (median = 46 years) were measured with L-cone- and rod-favoring CPC protocols. Linear-mixed effects models were performed to determine factors influencing the PLR and optical coherence tomography (OCT) data were correlated with the pupillary function volume.

Results

Relative maximal constriction amplitude (relMCA) and latency under L-cone- and rod-favoring stimulation were statistically significantly affected by the stimulus eccentricity (P < 0.0001, respectively). Iris color and gender did not affect relMCA or latency significantly; visual hemifield, season, and daytime showed only minor influence under few stimulus conditions. Age had a statistically significant effect on latency under rod-specific stimulation with a latency prolongation ≥60 years. Under photopic and scotopic conditions, baseline pupil diameter declined significantly with increasing age (P < 0.0001, respectively). Pupillary function volume and OCT data were not correlated relevantly.

Conclusions

Stimulus eccentricity had the most relevant impact on relMCA and latency of the PLR during L-cone- and rod-favoring stimulation. Latency is prolonged ≥60 years under scotopic conditions. Considering the large study collective, a representative normative database for relMCA and latency as valid readout parameters for L-cone- and rod-favoring stimulation could be established. This further validates the usability of the PLR in CPC as a biomarker for local retinal function.

Basics, benefits, and pitfalls of pupillometers assessing visual function

Numerous commercially and non-commercially available pupillometers are nowadays able to assess various biological functions in humans, by evaluating pupils' dynamics in response to specific stimuli. However, the use of pupillometers for ophthalmic afferent evaluations (i.e., photoreceptoral responses) in real-world settings is relatively limited. Recent scientific and technological advances, coupled with artificial intelligence methods have improved the performance of such devices to objectively detect, quantify, and classify functional disturbances of the retina and the optic nerve. This review aims to summarize the scientific principles, indications, outcomes, and current limitations of pupillometry used for evaluation of afferent pathways in ophthalmic clinical settings.

Comparison of Full-Field Stimulus Threshold Measurements in Patients With Retinitis Pigmentosa and Healthy Subjects With Dilated and Nondilated Pupil

Purpose

The common protocol of full-field stimulus threshold (FST) testing recommends pupil dilation. The aim of this study is to investigate the difference between FST measurements with dilated and nondilated pupils in healthy subjects and patients with retinitis pigmentosa (RP).

Methods

Twenty healthy subjects and 20 RP patients were selected. One pupil of each subject was dilated; the other eye was measured in physiological width of the pupil. The FST was conducted using Diagnosys Espion E2/E3 with white, blue, and red stimuli. Statistical analysis was conducted with a mixed-model analysis of variance and a paired t-test.

Results

The statistical analysis revealed a significant difference between measurements of dilated and nondilated pupils with the following: blue stimuli for all subjects and groups except those with highly progressed RP; white stimuli for all tested subjects in total, for RP patients with better-preserved visual field (VF), and rod-mediated FST response; and red stimuli for RP patients with better-preserved VF and rod-mediated FST response. On average, the difference between the FST values for RP patients were -3.2 ± 3 dB for blue, -2.3 ± 2.9 dB for white, and -0.83 ± 3 dB for red stimuli. The correlation between the FST values of dilated and nondilated pupils with all three stimuli was linear.

Conclusions

Current recommendations are to perform FST with dilated pupils. However, based on this study's findings, pupil dilation can be omitted for clinical diagnostics or rough follow-ups.

Translational Relevance

Our data provide useful information for the clinical use of FST.

ISCEV and IPS guideline for the full-field stimulus test (FST)

The full-field stimulus test (FST) is a psychophysical technique designed for the measurement of visual function in low vision. The method involves the use of a ganzfeld stimulator, as used in routine full-field electroretinography, to deliver full-field flashes of light. This guideline was developed jointly by the International Society for Clinical Electrophysiology of Vision (ISCEV) and Imaging and Perimetry Society (IPS) in order to provide technical information, promote consistency of testing and reporting, and encourage convergence of methods for FST. It is intended to aid practitioners and guide the formulation of FST protocols, with a view to future standardisation.

Full-field stimulus threshold testing: a scoping review of current practice

The full-field stimulus threshold (FST) is a psychophysical measure of whole-field retinal light sensitivity. It can assess residual visual function in patients with severe retinal disease and is increasingly being adopted as an endpoint in clinical trials. FST applications in routine ophthalmology clinics are also growing, but as yet there is no formalised standard guidance for measuring FST. This scoping review explored current variability in FST conduct and reporting, with an aim to inform further evidence synthesis and consensus guidance. A comprehensive electronic search and review of the literature was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis Extension for Scoping Reviews (PRISMA-ScR) checklist. Key source, participant, methodology and outcomes data from 85 included sources were qualitatively and quantitatively compared and summarised. Data from 85 sources highlight how the variability and insufficient reporting of FST methodology, including parameters such as units of flash luminance, colour, duration, test strategy and dark adaptation, can hinder comparison and interpretation of clinical significance across centres. The review also highlights an unmet need for paediatric-specific considerations for test optimisation. Further evidence synthesis, empirical research or structured panel consultation may be required to establish coherent standardised guidance on FST methodology and context or condition dependent modifications. Consistent reporting of core elements, most crucially the flash luminance equivalence to 0 dB reference level is a first step. The development of criteria for quality assurance, calibration and age-appropriate reference data generation may further strengthen rigour of measurement.

Clinical characterization of patients with PRPF31-related retinitis pigmentosa and asymptomatic carriers: a cross-sectional study

BACKGROUND/AIM

To describe the clinical phenotype of retinitis pigmentosa (RP) caused by PRPF31-variants and clinical characterization of asymptomatic PRPF31 carriers.

MATERIALS AND METHODS

We conducted a descriptive cross-sectional deep phenotyping study. We included subjects with PRPF31 variants predicted to be disease-causing, both individuals with RP and asymptomatic carriers. Participants underwent a comprehensive clinical examination of standard visual function parameters (visual acuity, contrast sensitivity, Goldmann visual field), full-field stimulus threshold (FST), full-field electroretinogram (ff-ERG), and a structural investigation with slit lamp and multimodal imaging. We used Spearman correlation analyses to evaluate associations between quantitative outcomes.

RESULTS

We included 21 individuals with disease-causing PRPF31-variants: 16 symptomatic and 5 asymptomatic subjects. The symptomatic subjects demonstrated a typical RP phenotype with constricted visual fields, extinguished ff-ERG, and disrupted outer retinal anatomy. FST was impaired and correlated significantly with other outcome measures in RP subjects. Structure-function correlations with Spearman correlation analysis showed moderate correlation coefficients due to a few outliers in each analysis. The asymptomatic individuals had normal best-corrected visual acuity and visual fields, but showed reduced ff-ERG amplitudes, borderline FST sensitivity, and structural abnormalities on OCT and fundoscopy.

CONCLUSIONS

RP11 has a typical RP phenotype but varies in terms of severity. FST measurements correlated well with other functional and structural metrics and may be a reliable outcome measure in future trials as it is sensitive to a broad range of disease severities. Asymptomatic carriers showed sub-clinical disease manifestations, and our findings underline that reported non-penetrance in PRPF31-related RP is not an all-or-none phenomenon.

Chromatic pupillometry isolation and evaluation of intrinsically photosensitive retinal ganglion cell-driven pupillary light response in patients with retinitis pigmentosa

Purpose

The pupil light response (PLR) is driven by rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs). We aimed to isolate ipRGC-driven pupil responses using chromatic pupillometry and to determine the effect of advanced retinitis pigmentosa (RP) on ipRGC function.

Methods

A total of 100 eyes from 67 patients with advanced RP and 18 healthy controls (HCs) were included. Patients were divided into groups according to severity of visual impairment: no light perception (NLP, 9 eyes), light perception (LP, 19 eyes), faint form perception (FFP, 34 eyes), or form perception (FP, 38 eyes). Pupil responses to rod-weighted (487 nm, -1 log cd/m2, 1 s), cone-weighted (630 nm, 2 log cd/m2, 1 s), and ipRGC-weighted (487 nm, 2 log cd/m2, 1 s) stimuli were recorded. ipRGC function was evaluated by the postillumination pupil response (PIPR) and three metrics of pupil kinetics: maximal contraction velocity (MCV), contraction duration, and maximum dilation velocity (MDV).

Results

We found a slow, sustained PLR response to the ipRGC-weighted stimulus in most patients with NLP (8/9), but these patients had no detectable rod- or cone-driven PLR. The ipRGC-driven PLR had an MCV of 0.269 ± 0.150%/s and contraction duration of 2.562 ± 0.902 s, both of which were significantly lower than those of the rod and cone responses. The PIPRs of the RP groups did not decrease compared with those of the HCs group and were even enhanced in the LP group. At advanced stages, ipRGC responses gradually became the main component of the PLR.

Conclusion

Chromatic pupillometry successfully isolated an ipRGC-driven PLR in patients with advanced RP. This PLR remained stable and gradually became the main driver of pupil contraction in more advanced cases of RP. Here, we present baseline data on ipRGC function; we expect these findings to contribute to evaluating and screening candidates for novel therapies.

Envisioning the development of a CRISPR-Cas mediated base editing strategy for a patient with a novel pathogenic CRB1 single nucleotide variant

BACKGROUND

Inherited retinal degeneration (IRD) associated with mutations in the Crumbs homolog 1 (CRB1) gene is associated with a severe, early-onset retinal degeneration for which no therapy currently exists. Base editing, with its capability to precisely catalyse permanent nucleobase conversion in a programmable manner, represents a novel therapeutic approach to targeting this autosomal recessive IRD, for which a gene supplementation is challenging due to the need to target three different retinal CRB1 isoforms.

PURPOSE

To report and classify a novel CRB1 variant and envision a possible therapeutic approach in form of base editing.

METHODS

Case report.

RESULTS

A 16-year-old male patient with a clinical diagnosis of early-onset retinitis pigmentosa (RP) and characteristic clinical findings of retinal thickening and coarse lamination was seen at the Oxford Eye Hospital. He was found to be compound heterozygous for two CRB1 variants: a novel pathogenic nonsense variant in exon 9, c.2885T>A (p.Leu962Ter), and a likely pathogenic missense change in exon 6, c.2056C>T (p.Arg686Cys). While a base editing strategy for c.2885T>A would encompass a CRISPR-pass mediated "read-through" of the premature stop codon, the resulting missense changes were predicted to be "possibly damaging" in in-silico analysis. On the other hand, the transversion missense change, c.2056C>T, is amenable to transition editing with an adenine base editor (ABE) fused to a SaCas9-KKH with a negligible chance of bystander edits due to an absence of additional Adenines (As) in the editing window.

CONCLUSIONS

This case report records a novel pathogenic nonsense variant in CRB1 and gives an example of thinking about a base editing strategy for a patient compound heterozygous for CRB1 variants.

CRB1-Associated Retinal Dystrophies: A Prospective Natural History Study in Anticipation of Future Clinical Trials

PURPOSE

To investigate the natural disease course of retinal dystrophies associated with crumbs cell polarity complex component 1 (CRB1) and identify clinical end points for future clinical trials.

DESIGN

Single-center, prospective case series.

METHODS

An investigator-initiated nationwide collaborative study that included 22 patients with CRB1-associated retinal dystrophies. Patients underwent ophthalmic assessment at baseline and 2 years after baseline. Clinical examination included best-corrected visual acuity (BCVA) using Early Treatment Diabetic Retinopathy Study charts, Goldmann kinetic perimetry (V4e isopter seeing retinal areas), microperimetry, full-field electroretinography, full-field stimulus threshold (FST), fundus photography, spectral-domain optical coherence tomography, and fundus autofluorescence imaging.

RESULTS

Based on genetic, clinical, and electrophysiological data, patients were diagnosed with retinitis pigmentosa (19 [86%]), cone-rod dystrophy (2 [9%]), or isolated macular dystrophy (1 [5%]). Analysis of the entire cohort at 2 years showed no significant changes in BCVA (P = .069) or V4e isopter seeing retinal areas (P = .616), although signs of clinical progression were present in individual patients. Macular sensitivity measured on microperimetry revealed a significant reduction at the 2-year follow-up (P < .001). FST responses were measurable in patients with nonrecordable electroretinograms. On average, FST responses remained stable during follow-up.

CONCLUSION

In CRB1-associated retinal dystrophies, visual acuity and visual field measures remain relatively stable over the course of 2 years. Microperimetry showed a significant decrease in retinal sensitivity during follow-up and may be a more sensitive progression marker. Retinal sensitivity on microperimetry may serve as a functional clinical end point in future human treatment trials for CRB1-associated retinal dystrophies.

Chromatic Full-Field Stimulus Thresholds in Patients with Treatment-Naive Age-Related Macular Degeneration

Purpose

To evaluate retinal sensitivity using chromatic full-field stimulus thresholds (FST) in patients with treatment naive exudative age-related macular degeneration (e-ARMD) before and during the first intravitreal anti-vascular endothelial growth factor (anti-VEGF) treatment.

Patients and Methods

After general ophthalmological examinations to diagnose patients with e-ARMD the FST, the central foveal thickness (FCt) and the visual acuity were assessed in 20 eyes of 20 patients during this prospective study. Examinations were performed before and during the first treatment series with three intravitreal anti-VEGF injections. Normal values for FST were assessed in 19 eyes of 19 healthy subjects. Results were analyzed using Student’s two-tailed t-test and Pearson’s correlation coefficients between all functional parameters.

Results

At baseline and before the 1st intravitreal anti-VEGF treatment, a moderately significant negative correlation between VA and FCt was found in the e-ARMD group (p = 0.02, r = −0.45 and p = 0.03, r = −0.45), respectively. After the 2nd intravitreal anti-VEGF injection, no significant correlation between VA and FCt was found (p = 0.12). However, a significant correlation between FCt and blue FST was evident (p = 0.04, r = 0.4). After the 3rd intravitreal anti-VEGF treatment, there was no correlation evident between VA and FCt (p = 0.31) but a high significant correlation between FCt and FST using red (p = 0.01, r = 0.53), green (p = 0.002, r = 0.6) and blue light (p = 0.007, r = 0.66).

Conclusion

During anti-VEGF treatment in patients with e-ARMD, the FST test showed higher significant correlations with the morphology measured by FCt, as it is the case for VA. These findings support that the FST test might serve as a valuable diagnostic tool for monitoring patients with e-ARMD and enhance functional assessment of retinal function under treatment with anti-VEGF.

How lesions at different locations along the visual pathway influence pupillary reactions to chromatic stimuli

PURPOSE

To examine systematically how prechiasmal, chiasmal, and postchiasmal lesions along the visual pathway affect the respective pupillary responses to specific local monochromatic stimuli.

METHODS

Chromatic pupil campimetry (CPC) was performed in three patient groups (10 subjects with status after anterior ischemic optic neuropathy, 6 with chiasmal lesions, and 12 with optic tract or occipital lobe lesions (tumor, ischemia)) using red, low-intensity red, and blue local stimuli within the central 30° visual field. Affected areas - as determined by visual field defects revealed using conventional static perimetry - were compared with non-affected areas. Outcome parameters were the relative maximal constriction amplitude (relMCA) and the latency to constriction onset of the pupillary responses.

RESULTS

A statistically significant relMCA reduction was observed in the affected areas of postchiasmal lesions with red (p = 0.004) and low-intensity red stimulation (p = 0.001). RelMCA reduction in the affected areas seemed more pronounced for low-intensity red stimulation (46.5% mean reduction compared to non-affected areas; 36% for red stimulation), however statistically not significant. In prechiasmal lesions, a statistically significant latency prolongation could be demonstrated in the affected areas with low-intensity red stimulation (p = 0.015).

CONCLUSION

Our results indicate that the choice of stimulus characteristics is relevant in detecting defects in the pupillary pathway of impairment along the visual pathway, favoring red stimuli of low intensity over blue stimuli. Such knowledge opens the door for further fundamental research in pupillary pathways and is important for future clinical application of pupillography in neuro-ophthalmologic patients.

Effect of central and peripheral cone- and rod-specific stimulation on the pupillary light reflex

Purpose

To assess the effect of central and peripheral stimulation on the pupillary light reflex. The aim was to detect possible differences between cone- and rod-driven reactions.

Methods

Relative maximal pupil constriction amplitude (relMCA) and latency to constriction onset (latency) to cone- and rod-specific stimuli of 30 healthy participants (24 ± 5 years (standard deviation)) were measured using chromatic pupil campimetry. Cone- and rod-specific stimuli had different intensities and wavelengths according to the Standards in Pupillography. Five filled circles with radii of 3°, 5°, 10°, 20° and 40° and four rings with a constant outer radius of 40° and inner radii of 3°, 5°, 10° and 20° were used as stimuli.

Results

For cone-and rod-specific stimuli, relMCA increased with the stimulus area for both, circles and rings. However, increasing the area of a cone-specific ring by minimizing its inner radius with constant outer radius increased relMCA significantly stronger than the same did for a rod-specific ring. For cones and rods, a circle stimulus with a radius of 40° created a lower relMCA than the summation of the relMCAs to the corresponding ring and circle stimuli which combined create a 40° circle-stimulus. Latency was longer for rods than for cones. It decreased with increasing stimulus area for circle stimuli while it stayed nearly constant with increasing ring stimulus area for cone- and rod-specific stimuli.

Conclusion

The effect of central stimulation on relMCA is more dominant for cone-specific stimuli than for rod-specific stimuli while latency dynamics are similar for both conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10792-021-02132-1.

Voretigene Neparvovec Gene Therapy in Clinical Practice: Treatment of the First Two Italian Pediatric Patients

Purpose

To present visual outcomes of the first two Italian patients with RPE65-related inherited retinal dystrophy (RPE65-IRD) treated with voretigene neparvovec (VN).

Methods

Two pediatric patients with RPE65-IRD were treated with VN in both eyes. Patients were evaluated by best-corrected visual acuity (BCVA), full-field stimulus threshold (FST) test, semiautomated kinetic visual field (SKVF), microperimetry, and chromatic pupillometry over 6 months.

Results

No complications occurred in the first patient, whereas in the second a subretinal hemorrhage was observed in the first treated eye, and excessive resistance to drug injection occurred during treatment of the second eye. BCVA improved by at least one Early Treatment Diabetic Retinopathy Study line in all treated eyes. The FST test and SKVF showed clinically significant improvements in all eyes (i.e., change of light sensitivity > 10 decibels; area enlargement of at least 20%). Moreover, microperimetry showed better fixation stability. Finally, chromatic pupillometry showed increases in pupillary constriction that ranged from 10% to 20%. All visual changes remained stable during follow-up.

Conclusions

The first VN treatments in two pediatric Italian patients in clinical practice showed significant improvements in visual outcomes, even in the case of surgical complications, which spontaneously recovered without sequelae.

Translational Relevance

These findings with VN in patients with RPE65-IRD confirm the results of clinical trials.

Multimodal Retinal Imaging and Microperimetry Reveal a Novel Phenotype and Potential Trial End Points in CRB1-Associated Retinopathies

Purpose

Biallelic crumbs cell polarity complex component 1 (CRB1) mutations can present as Leber congenital amaurosis (LCA), retinitis pigmentosa (RP), or cystic maculopathy. This study reports a novel phenotype of asymptomatic fenestrated slit maculopathy (AFSM) and examines macular volume profile and microperimetry as clinical trial end points in CRB1-associated retinopathies.

Methods

Twelve patients from nine families with CRB1 mutation were recruited. Ultra-widefield (UWF) color fundus photography and autofluorescence (AF), spectral-domain optical coherence tomography (SD-OCT), microperimetry, and adaptive optics (AO) imaging were performed. Macular volume profiles were compared with age-matched healthy controls. Genotyping was performed using APEX genotyping microarrays, targeted next-generation sequencing, and Sanger sequencing.

Results

We identified one patient with LCA, five patients with RP, and four patients with macular dystrophy (MD) with biallelic CRB1 mutations. Two siblings with compound heterozygote genotype (c.[2843G>A]; [498_506del]) had AFSM characterized by localized outer retinal disruption on SD-OCT and parafoveal cone loss on AO imaging despite normal fundus appearance, visual acuity, and foveal sensitivity. UWF AF demonstrated preserved para-arteriolar retinal pigment epithelium (PPRPE) in all patients with RP. Microperimetry documented preserved central retinal function in six patients. The ratio of perifoveal-to-foveal retinal volume was greater than controls in 89% (8/9) of patients with RP or MD, whereas central subfield and total macular volume were outside normal limits in 67% (6/9).

Conclusions

AO imaging was helpful in detecting parafoveal cone loss in asymptomatic patients. Macular volume profile and microperimetry parameters may have utility as CRB1 trials end points.

Translational Relevance

Macular volume and sensitivity can be used as structural and functional end points for trials on CRB1-associated RP and MD.

Transient pupillary light reflex in CEP290- or NPHP5-associated Leber congenital amaurosis: Latency as a potential outcome measure of cone function

Mutations in photoreceptor cilium genes CEP290 and NPHP5 cause a form of Leber congenital amaurosis (LCA) which typically lacks rods but retains central cones. The current study evaluated the transient pupillary light reflex (TPLR) as an objective outcome measure to assess efficacy of ongoing and future therapies. Eleven eyes of six patients selected for retained cone function were tested with TPLR using full-field stimuli in the dark-adapted state. Stimuli were red or blue with 1 s duration and spanned a 6-log unit dynamic range. TPLR response amplitude was quantified at fixed times of 0.9 and 2 s after stimulus onset and TPLR latency was defined as the time to reach 0.3 mm constriction. Full-field stimulus testing (FST) and static perimetry were used to correlate subjective perception with objective TPLR parameters. TPLR and FST thresholds with both red and blue stimuli were abnormally elevated in patients to near -1.25 log phot-cd·m-2 consistent with the lack of rods. TPLR latencies were delayed on average but showed some differences among patients. Remnant extrafoveal vision was correlated with faster TPLR latencies. Our results support the use of a short TPLR protocol with full-field red stimuli of 0.7 log phot-cd·m-2 or brighter as an objective and convenient outcome measure of cone function in CEP290- and NPHP5-LCA. The latency parameter of the TPLR would be expected to show a detectable change when an intervention modifies cone sensitivity in the extrafoveal region.