VASCULAR ALTERATIONS REVEALED WITH OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN PATIENTS WITH CHOROIDEREMIA

Retinal vascular reactivity in carriers of X-linked inherited retinal disease - a study using optical coherence tomography angiography

Purpose

Female carriers of X-linked inherited retinal diseases (IRDs) can show highly variable phenotypes and disease progression. Vascular reactivity, a potential disease biomarker, has not been investigated in female IRD carriers. In this study, functional optical coherence tomography angiography (OCT-A) was used to dynamically assess the retinal microvasculature of X-linked IRD carriers.

Methods

Genetically confirmed female carriers of IRDs (choroideremia or X-linked retinitis pigmentosa), and healthy women were recruited. Macular angiograms (3x3mm, Zeiss Plex Elite 9000) were obtained in 36 eyes of 15 X-linked IRD female carriers and 21 age-matched control women. Two tests were applied to test vascular reactivity: (i) mild hypoxia and (ii) handgrip test, to induce a vasodilatory or vasoconstrictive response, respectively. Changes to vessel density (VD) and vessel length density (VLD) were independently evaluated during each of the tests for both the superficial and deep capillary plexuses.

Results

In the control group, the superficial and deep VD decreased during the handgrip test (p<0.001 and p=0.037, respectively). Mean superficial VLD also decreased during the handgrip test (p=0.025), while the deep plexus did not change significantly (p=0.108). During hypoxia, VD and VLD increased in the deep plexus (p=0.027 and p=0.052, respectively) but not in the superficial plexus. In carriers, the physiologic vascular responses seen in controls were not observed in either plexus during either test, with no difference in VD or VLD noted (all p>0.05).

Conclusions

Functional OCT-A is a useful tool to assess dynamic retinal microvascular changes. Subclinical impairment of the physiological vascular responses seen in carriers of X-linked IRDs may serve as a valuable clinical biomarker.

Optical coherence tomography in children with inherited retinal disease

Recent advances have led to therapeutic options becoming available for people with inherited retinal disease. In particular, gene therapy has been shown to hold great promise for slowing vision loss from inherited retinal disease. Recent studies suggest that gene therapy is likely to be most effective when implemented early in the disease process, making consideration of paediatric populations important. It is therefore necessary to have a comprehensive understanding of retinal imaging in children with inherited retinal diseases, in order to monitor disease progression and to determine which early retinal biomarkers may be used as outcome measures in future clinical trials. In addition, as many optometrists will review children with an inherited retinal disease, an understanding of the expected imaging outcomes can improve clinical care. This review focuses on the most common imaging modality used in research assessment of paediatric inherited retinal diseases: optical coherence tomography. Optical coherence tomography findings can be used in both the clinical and research setting. In particular, the review discusses current knowledge of optical coherence tomography findings in eight paediatric inherited retinal diseases - Stargardt disease, Bests disease, Leber's congenital amaurosis, choroideremia, RPGR related retinitis pigmentosa, Usher syndrome, X-linked retinoschisis and, Batten disease.

Loss of REP1 impacts choroidal melanogenesis and vasculogenesis in choroideremia

Choroideremia (CHM) is a rare X-linked chorioretinal dystrophy affecting the photoreceptors, retinal pigment epithelium (RPE) and choroid, however, the involvement of the choroid in disease progression is not fully understood. CHM is caused by mutations in the CHM gene, encoding the ubiquitously expressed Rab escort protein 1 (REP1). REP1 plays an important role in intracellular trafficking of vesicles, including melanosomes. In this study, we examined the ultrastructure of the choroid in chmru848 fish and Chmnull/WT mouse models using transmission electron and confocal microscopy. Significant pigmentary disruptions were observed, with lack of melanosomes in the choroid of chmru848 fish from 4 days post fertilisation (4dpf), and a reduction in choroidal blood vessel diameter and interstitial pillars suggesting a defect in vasculogenesis. Total melanin and expression of melanogenesis genes tyr, tryp1a, mitf, dct and pmel were also reduced from 4dpf. In Chmnull/WT mice, choroidal melanosomes were significantly smaller at 1 month, with reduced eumelanin at 1 year. The choroid in CHM patients were also examined using spectral domain optical coherence tomography (SD-OCT) and OCT-angiography (OCT-A) and the area of preserved choriocapillaris (CC) was found to be smaller than that of overlying photoreceptors, suggesting that the choroid is degenerating at a faster rate. Histopathology of an enucleated eye from a 74-year-old CHM male patient revealed isolated areas of RPE but no associated underlying CC. Pigmentary disruptions in CHM animal models reveal an important role for REP1 in melanogenesis, and drugs that improve melanin production represent a potential novel therapeutic avenue.

Optical coherence tomography angiography in Bietti crystalline dystrophy

PURPOSE

Bietti crystalline dystrophy (BCD) is a rare autosomal recessive retinal dystrophy caused by pathogenic variants of CYP4V2 gene and characterized by shiny yellow deposits in the retina and progressive atrophy of the retinal pigment epithelium (RPE) and choriocapillaris. The main aim of the present study is to describe the optical coherence tomography angiography (OCTA) characteristics of a patient affected by BCD.

METHODS

A 59-years-old female with genetically confirmed BCD underwent an ophthalmological examination complete of OCTA performed in the atrophic retina, the junctional zone and the apparently normal retina. The area of choriocapillaris (CC) atrophy was compared to the area of RPE atrophy on fundus autofluorescence (FAF) imaging.

RESULTS

A severe vessel density (VD) deficit at the level of superficial and deep capillary plexa as well as CC was registered in atrophic areas, which resulted deeper with respect to the junctional area, whereas the apparently preserved retina revealed VD values similar to that of control eyes. The area of RPE atrophy on FAF was larger (55.90 mm2 in right eye and 48.76 mm2 in left eye) than the area of CC atrophy on OCTA imaging (51.86 mm2 and 42.44 mm2 respectively in right and left eye).

CONCLUSIONS

Our findings suggest that VD impairment of retinal plexa and CC follows the degeneration of RPE as demonstrated by the greater size of the area of RPE atrophy compared to CC atrophy. Further investigations based on OCTA imaging are necessary to enhance our knowledge of this rare disease.

Choroideremia: The Endpoint Endgame

Choroideremia is an X-linked retinal degeneration resulting from the progressive, centripetal loss of photoreceptors and choriocapillaris, secondary to the degeneration of the retinal pigment epithelium. Affected individuals present in late childhood or early teenage years with nyctalopia and progressive peripheral visual loss. Typically, by the fourth decade, the macula and fovea also degenerate, resulting in advanced sight loss. Currently, there are no approved treatments for this condition. Gene therapy offers the most promising therapeutic modality for halting or regressing functional loss. The aims of the current review are to highlight the lessons learnt from clinical trials in choroideremia, review endpoints, and propose a future strategy for clinical trials.

Cone Photoreceptor Morphology in Choroideremia Assessed Using Non-Confocal Split-Detection Adaptive Optics Scanning Light Ophthalmoscopy

Purpose

Choroideremia (CHM) is an X-linked inherited retinal degeneration causing loss of the photoreceptors, retinal pigment epithelium, and choriocapillaris, although patients typically retain a central island of relatively preserved, functioning retina until late-stage disease. Here, we investigate cone photoreceptor morphology within the retained retinal island by examining cone inner segment area, density, circularity, and intercone space.

Methods

Using a custom-built, multimodal adaptive optics scanning light ophthalmoscope, nonconfocal split-detection images of the photoreceptor mosaic were collected at 1°, 2°, and 4° temporal to the fovea from 13 CHM and 12 control subjects. Cone centers were manually identified, and cone borders were segmented. A custom MATLAB script was used to extract area and circularity for each cone and calculate the percentage of intercone space in each region of interest. Bound cone density was also calculated. An unbalanced two-way ANOVA and Bonferroni post hoc tests were used to assess statistical differences between the CHM and control groups and along retinal eccentricity.

Results

Cone density was lower in the CHM group than in the control group (P < 0.001) and decreased with eccentricity from the fovea (P < 0.001). CHM cone inner segments were larger in area (P < 0.001) and more circular (P = 0.042) than those of the controls. Intercone space in CHM was also higher than in the controls (P < 0.001).

Conclusions

Cone morphology is altered in CHM compared to control, even within the centrally retained, functioning retinal area. Further studies are required to determine whether such morphology is a precursor to cone degeneration.

Clinical Applications of Optical Coherence Tomography Angiography in Inherited Retinal Diseases: An Up-to-Date Review of the Literature

Optical coherence tomography angiography (OCT-A) is a valuable imaging technique, allowing non-invasive, depth-resolved, motion-contrast, high-resolution images of both retinal and choroidal vascular networks. The imaging capabilities of OCT-A have enhanced our understanding of the retinal and choroidal alterations that occur in inherited retinal diseases (IRDs), a group of clinically and genetically heterogeneous disorders that may be complicated by several vascular conditions requiring a prompt diagnosis. In this review, we aimed to comprehensively summarize all clinical applications of OCT-A in the diagnosis and management of IRDs, highlighting significant vascular findings on retinitis pigmentosa, Stargardt disease, choroideremia, Best disease and other less common forms of retinal dystrophies. All advantages and limitations of this novel imaging modality will be also discussed.

Outer retinal and choriocapillaris modifications in choroideremia: three differentially impaired retinal regions and the potential diagnostic role of the external limiting membrane

BACKGROUND

The external limiting membrane (ELM) is formed by the apical processes of Müller cells attached to the inner segments of the photoreceptor cells. Both cells are implicated in the pathogenesis of choroideremia (CHM). The purpose of this study was to explore the diagnostic role of ELM in CHM.

METHODS

The study was designed as observational case series. Sixteen CHM eyes were examined by multimodal imaging and were compared to healthy controls. The main outcome was the measurement of ELM thickness and reflectivity over the follow-up, and its relationship with other multimodal imaging quantitative parameters.

RESULTS

Baseline ELM was characterized by 11 ± 1 µm of thickness and 0.68 ± 0.13 of reflectivity, resulting 8 ± 1 µm (p < 0.01) and 0.65 ± 0.14 (p > 0.05) at the last follow-up. Choriocapillaris (CC) analysis revealed 3 regions. The first was characterized by normal vessel density (VD). The second surrounding the partially preserved islet, showing significantly lower baseline VD and undergoing minor changes over the follow-up. The third was localized in the partially preserved islet, showing significantly lower VD at baseline, and resulted atrophic at the last follow-up. ELM reflectivity and ELM thickness correlated both with outer retinal atrophy progression and the CC status.

CONCLUSIONS

ELM may be considered a useful imaging biomarker in CHM. Its assessment confirmed a primary role of Müller cells impairment in the pathogenesis of CHM.

Gene Therapy in Inherited Retinal Diseases: An Update on Current State of the Art

Background: Gene therapy cannot be yet considered a far perspective, but a tangible therapeutic option in the field of retinal diseases. Although still confined in experimental settings, the preliminary results are promising and provide an overall scenario suggesting that we are not so far from the application of gene therapy in clinical settings. The main aim of this review is to provide a complete and updated overview of the current state of the art and of the future perspectives of gene therapy applied on retinal diseases.

Methods: We carefully revised the entire literature to report all the relevant findings related to the experimental procedures and the future scenarios of gene therapy applied in retinal diseases. A clinical background and a detailed description of the genetic features of each retinal disease included are also reported.

Results: The current literature strongly support the hope of gene therapy options developed for retinal diseases. Although being considered in advanced stages of investigation for some retinal diseases, such as choroideremia (CHM), retinitis pigmentosa (RP), and Leber's congenital amaurosis (LCA), gene therapy is still quite far from a tangible application in clinical practice for other retinal diseases.

Conclusions: Gene therapy is an extremely promising therapeutic tool for retinal diseases. The experimental data reported in this review offer a strong hope that gene therapy will be effectively available in clinical practice in the next years.

Optical Coherence Tomography Angiography in the Thirteen-Lined Ground Squirrel

Purpose

To assess the performance of two spectral-domain optical coherence tomography-angiography systems in a natural model of hypoperfusion: the hibernating thirteen-lined ground squirrel (13-LGS).

Methods

Using a high-speed (130 kHz) OCT-A system (HS-OCT-A) and a commercial OCT (36 kHz; Bioptigen Envisu; BE-OCT-A), we imaged the 13-LGS retina throughout its hibernation cycle. Custom software was used to extract the superior, middle, and deep capillary plexus (SCP, MCP, and DCP, respectively). The retinal vasculature was also imaged with adaptive optics scanning light ophthalmoscopy (AOSLO) during torpor to visualize individual blood cells. Finally, correlative histology with immunolabeled or DiI-stained vasculature was performed.

Results

During euthermia, vessel density was similar between devices for the SCP and MCP (P = 0.88, 0.72, respectively), with a small difference in the DCP (−1.63 ± 1.54%, P = 0.036). Apparent capillary dropout was observed during torpor, but recovered after forced arousal, and this effect was exaggerated in high-speed OCT-A imaging. Based on cell flux measurements with AOSLO, increasing OCT-A scan duration by ∼1000× would avoid the apparent capillary dropout artifact. High correspondence between OCT-A (during euthermia) and histology enabled lateral scale calibration.

Conclusions

While the HS-OCT-A system provides a more efficient workflow, the shorter interscan interval may render it more susceptible to the apparent capillary dropout artifact. Disambiguation between capillary dropout and transient ischemia can have important implications in the management of retinal disease and warrants additional diagnostics.

Translational Relevance

The 13-LGS provides a natural model of hypoperfusion that may prove valuable in modeling the utility of OCT-A in human pathologies associated with altered blood flow.

Stage-dependent choriocapillaris impairment in Best vitelliform macular dystrophy characterized by optical coherence tomography angiography

Characterization of vascular impairment in Best vitelliform macular dystrophy (BVMD) is essential for the development of treatment modalities and therapy trials. As such, we seek to characterize the choriocapillaris (CC) at each stage of the disease process in 22 patients (44 eyes) with a diagnosis of BVMD confirmed by genetic sequencing. We utilize optical coherence tomography angiography (OCTA) images to characterize the CC and correlate our findings to the status of the retinal pigment epithelium (RPE) as observed on short-wavelength fundus autofluorescence (SW-AF) images. We observed that in the vitelliruptive stage, the CC appeared as bright and granular in the area where the vitelliform lesion was present. In the atrophic stage, varying degrees of CC atrophy were observed within the lesion area, with the regions of CC atrophy appearing as hypoautofluorescent on SW-AF images. Our results suggest that the CC impairment observed in the vitelliruptive stage of BVMD progressively culminates in the CC atrophy observed at the atrophic stage. As such, OCTA imaging can be used to characterize CC impairment in BVMD patients as part of diagnosis and tracking of disease progression. Our findings suggest that the best window of opportunity for therapeutic approaches is before the atrophic stage, as it is during this stage that CC atrophy is observed.

Total flow intensity, active flow intensity and volume related flow intensity as new quantitative metrics in optical coherence tomography angiography

Optical coherence tomography (OCT) angiography (OCTA) is a non-invasive tool for the in-vivo study of the intraretinal vascular network. It is based on the analysis of motion particles within the retina to reconstruct the paths followed by the erythrocytes, i.e. retinal capillaries. To date, qualitative and quantitative information are based on the morphological features disclosed by retinal capillaries. In the present study, we proposed new quantitative functional metrics, named Total Flow Intensity (TFI), Active Flow Intensity (AFI), and Volume-related Flow Intensity (VFI), based on the processing of the blood flow signal detected by OCTA. We studied these metrics in a cohort of healthy subjects, and we assessed their clinical utility by including a cohort of age-matched patients affected by Stargardt disease. Moreover, we compared TFI, AFI, and VFI to the widely used vessel density (VD) parameter. TFI, AFI, and VFI were able to describe in detail the different properties of the retinal vascular compartment. In particular, TFI was intended as the overall amount of volumetric retinal blood flow. AFI represented a selective measure of voxels disclosing blood flow signal. VFI was developed to put in relationship the volumetric blood flow information with the not vascularized retinal volume. In conclusion, TFI, AFI, and VFI were proposed as feasible functional OCTA biomarkers based on the analysis of retinal blood flow signal.

Prospective deep phenotyping of choroideremia patients using multimodal structure-function approaches

OBJECTIVE

To investigate the retinal changes in choroideremia (CHM) patients to determine correlations between age, structure and function.

SUBJECTS/METHODS

Twenty-six eyes from 13 male CHM patients were included in this prospective longitudinal study. Participants were divided into <50-year (n = 8) and ≥50-year (n = 5) old groups. Patients were seen at baseline, 6-month, and 1-year visits. Optical coherence tomography (OCT), OCT angiography, and fundus autofluorescence were performed to measure central foveal (CFT) and subfoveal choroidal thickness (SCT), as well as areas of preserved choriocapillaris (CC), ellipsoid zone (EZ), and autofluorescence (PAF). Patients also underwent functional investigations including visual acuity (VA), contrast sensitivity (CS), colour testing, microperimetry, dark adaptometry, and handheld electroretinogram (ERG). Vision-related quality-of-life was assessed by using the NEI-VFQ-25 questionnaire.

RESULTS

Over the 1-year follow-up period, progressive loss was detected in SCT, EZ, CC, PAF, and CFT. Those ≥50-years exhibited more structural and functional defects with SCT, EZ, CC, and PAF showing strong correlation with patient age (rho ≤ -0.47, p ≤ 0.02). CS and VA did not change over the year, but CS was significantly correlated with age (rho = -0.63, p = 0.001). Delayed to unmeasurable dark adaptation, decreased colour discrimination and no detectable ERG activity were observed in all patients. Minimal functional deterioration was observed over one year with a general trend of slower progression in the ≥50-years group.

CONCLUSIONS

Quantitative structural parameters including SCT, CC, EZ, and PAF are most useful for disease monitoring in CHM. Extended follow-up studies are required to determine longitudinal functional changes.

CHM mutation spectrum and disease: An update at the time of human therapeutic trials

Choroideremia is an X-linked inherited retinal disorder (IRD) characterized by the degeneration of retinal pigment epithelium, photoreceptors, choriocapillaris and choroid affecting males with variable phenotypes in female carriers. Unlike other IRD, characterized by a large clinical and genetic heterogeneity, choroideremia shows a specific phenotype with causative mutations in only one gene, CHM. Ongoing gene replacement trials raise further interests in this disorder. We describe here the clinical and genetic data from a French cohort of 45 families, 25 of which carry novel variants, in the context of 822 previously reported choroideremia families. Most of the variants represent loss-of-function mutations with eleven families having large (i.e. ≥6 kb) genomic deletions, 18 small insertions, deletions or insertion deletions, six showing nonsense variants, eight splice site variants and two missense variants likely to affect splicing. Similarly, 822 previously published families carry mostly loss-of-function variants. Recurrent variants are observed worldwide, some of which linked to a common ancestor, others arisen independently in specific CHM regions prone to mutations. Since all exons of CHM may harbor variants, Sanger sequencing combined with quantitative polymerase chain reaction or multiplex ligation-dependent probe amplification experiments are efficient to achieve the molecular diagnosis in patients with typical choroideremia features.

Multimodal imaging in subclinical best vitelliform macular dystrophy

BACKGROUND

To analyse multimodal imaging alterations in the subclinical form of best vitelliform macular dystrophy (BVMD).

METHODS

The study was designed as an observational, cross-sectional case series. Eleven eyes of 7 subclinical patients with BVMD and 12 age-matched and sex-matched controls were included. Multimodal imaging included fundus blue-light autofluorescence, near-infrared autofluorescence (NIR-AF), structural optical coherence tomography (OCT) and OCT angiography (OCTA). The quantitative analysis included the calculation of the following parameters: vessel density (VD), vessel tortuosity (VT), vessel dispersion (Vdisp), vessel rarefaction (VR), foveal avascular zone (FAZ) area, reflectivity of the outer retinal bands and choriocapillaris porosity (CCP).

RESULTS

Mean best-corrected visual acuity was 0.0±0.0 LogMAR in both groups. The round central hypoautofluorescent alteration on NIR-AF corresponded to a significant reflectivity attenuation of the outer retinal bands on structural OCT (0.55±0.18 vs 0.75±0.08; p<0.001). VD, VT, VR and Vdisp were normal compared with controls (all p>0.05). The FAZ area turned out to be significantly restricted at the level of the deep capillary plexus in subclinical BVMD eyes (p<0.001). Furthermore, quantitative OCTA revealed a significant central increase of CCP, compared with controls (18.25±2.43 vs 4.58±1.36; p<0.001).

CONCLUSIONS

The subclinical stage of BVMD is characterised by significant alterations of the outer retinal bands and the choriocapillaris. Quantitative multimodal imaging assessment suggests that subclinical BVMD is affected by the functional impairment of the outer retinal structures, leading to an alteration in melanin and growth factor production.

Analysis of optical coherence angiography in cystoid macular oedema associated with gyrate atrophy

BACKGROUND

To evaluate the relationship between superficial, deep foveal avascular zone (FAZ) and foveal cyst areas in eyes with cystoid macular oedema (CMO) associated with gyrate atrophy of the choroid and retina (GA).

METHODS

This is a retrospective collaborative multicenter study of optical coherence tomography-angiography (OCTA) images in GA. Superficial and deep FAZ and foveal cyst were measured using Image J by two independent experts. Values were corrected for myopia magnification. These values were compared with age-matched controls from normative data.

RESULTS

Twenty-three eyes from 12 patients with GA and CMO were included in the study. The mean ± standard deviation age was 22 ± 19.7 years, mean Snellen spectacle-corrected visual acuity of 20/70 with mean myopia of 5.7 ± 4.1 dioptres. Qualitatively, no focal occlusion of superficial and deep capillary plexus was noted. Mean superficial FAZ area (0.484 ± 0.317 mm²), deep FAZ area (0.626 ± 0.452 mm²), and foveal cyst area (0.630 ± 0.503 mm²) were significantly larger than superficial and deep FAZ areas in controls of same age range (p < 0.001). Macular cyst area correlated with superficial FAZ area (R = 0.59; p = 0.0057) and more strongly with deep FAZ area (R = 0.69; p < 0.001).

CONCLUSIONS

The superficial and deep FAZ area in GA-associated CMO were noted to be significantly larger than in controls. It seems that RPE dysfunction leads to foveal cyst enlargement displacing the capillary plexus with resultant enlarged superficial and deep FAZ area.

Progressive Choriocapillaris Impairment in ABCA4 Maculopathy Is Secondary to Retinal Pigment Epithelium Atrophy

Purpose

To analyze the progression of choriocapillaris (CC) impairment in recessive Stargardt disease (STGD) and compare it to the progression of retinal pigment epithelium (RPE) atrophy.

Methods

Fifty-five patients with a clinical diagnosis of STGD and genetic confirmation of pathogenic biallelic variants in ABCA4 were imaged with short-wavelength fundus autofluorescence (SW-AF) and optical coherence tomography angiography (OCTA) at a single clinic visit, whereas a subset of 12 patients were imaged with the same modalities at two different clinic visits.

Results

We observed three stages of CC impairment: an area of bright yet intact macular CC (11 patients), regions of vascular rarefaction and incomplete CC atrophy within an area of bright CC (10 patients), and areas of extensive CC atrophy (26 patients). These changes correlated to the degree of RPE atrophy observed in SW-AF imaging. Furthermore, 8 patients presented with early changes on SW-AF, but healthy CC. Quantitative analyses of the atrophic changes revealed that the area of RPE atrophy is larger (9.6 ± 1.7 mm2 vs. 6.9 ± 1.3 mm2, P < 0.001) and that it progresses at a faster rate (1.1 ± 0.1 mm2/year vs. 0.8 ± 0.2 mm2/year, P = 0.004) than the corresponding area of CC atrophy.

Conclusions

CC impairment is progressive and OCTA imaging can be used to demonstrate the stages, which culminate in extensive CC atrophy. Furthermore, CC impairment is secondary to RPE atrophy in STGD. We further advocate the use of SW-AF and OCTA imaging in monitoring the progression of STGD.

Reduced vessel density in deep capillary plexus correlates with retinal layer thickness in choroideremia

Background

To assess retinal layer thickness in choroideremia (CHM) and to reveal its correlation with optical coherence tomography (OCT) angiography (OCTA) findings.

Methods

The study was designed as an observational, cross-sectional clinical series of patients with CHM, which included 14 CHM eyes and 14 age-matched controls. Multimodal imaging included OCT and OCTA. The vessel density (VD) of superficial capillary (SCP), deep capillary (DCP) and choriocapillaris (CC) plexuses was analysed by OCTA. The apparently preserved retinal islet and atrophic regions were investigated separately. Main outcome measures were as follows: best-corrected visual acuity (BCVA), total retinal layers, ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), ellipsoid zone–retinal pigment epithelium (EZ-RPE) layer, choroidal thickness and VDs of SCP, DCP and of CC.

Results

Mean BCVA was 0.0±0.0 LogMAR in both groups. GCL, ONL, EZ-RPE and choroid were significantly thinned in CHM, particularly in the atrophic region. OPL was unaffected in the apparently preserved islet, whereas INL and IPL were similarly thinned in the atrophic and apparently preserved retina. DCP appeared severely affected in both regions, while CC was only altered in the atrophic retina. Significant correlations were found between OCT and OCTA parameters.

Conclusions

Our study showed severe alterations in both outer and inner retinal layers of patients with CHM. The extended retinal involvement might be the consequence of neuronal and vascular trophic factor reduction produced by the primarily altered RPE and/or secondary Müller glial cell reaction.

Optical Coherence Tomography Angiography (OCT-A) in Choroideremia (CHM) carriers

Purposes: To explore OCT-A abnormalities in CHM carriersMethods: CHM carriers and age-matched controls were consecutively enrolled at the Eye Clinic in Florence. All patients underwent a complete ophthalmic examination, fundus photography, fundus autofluorescence (FAF) and OCT examinations. OCT-A images of the superficial capillary plexus (SCP), deep capillary plexus (DCP) and choriocapillaris slab (CC) were acquired and analyzed using ImageJ software to detect and quantify vascular density.Results: Six patients (12 eyes) and 8 age-matched controls (16 eyes) were included in our study. The mean age was 45.5 ± 16.3 years (range 15-61) for the CHM carriers and 46.6 ± 12.2 (range 18-54) for controls. All CHM carriers showed fundus abnormalities. The detected mean central retinal thickness (CRT) (220 ± 18.34 vs 227 ± 15.46; p = .342) and choroidal central thickness (CCT) (271 ± 54.28 vs 275 ± 38.36; p = .760) did not differ between the carrier and the control group, respectively. Quantitative analysis of the inner retinal vasculature disclosed no significant difference of both SCP (p = .437) and DCP (p = .859) vessel density compared to the control group. Of note, a mild reduction on the vascular flow of the CC could be detected in the carrier group compared to the control group (78.896 ± 13.972 vs 80.008 ± 10.862; p = .045).Conclusions: OCT-A allows us to underline the role of the retinal pigment epithelium in the CHM pathophysiology. Central inner retinal and choriocapillaris vascularization were preserved although the RPE was always involved in the CHM carrier: this could support a secondary role of vascular impairment in the natural history of the disease.

En face OCT in choroideremia

Purpose: To describe the outer retinal tubulation (ORT) morphology using En face OCT elaboration in a large group of patients affected by choroideremia (CHM).Material and Methods: We retrospectively reviewed CHM patients examined at the Regional Reference Center for Hereditary Retinal Degenerations at the Eye Clinic in Florence. We took into consideration genetically confirmed CHM patients with ophthalmological, fundus autofluorescence (FAF) and optical coherence tomography (OCT) examinations.Results: We studied en face OCT features of ORTs in 18 CHM patients, for a total of 36 eyes; (average age 33 years; SD 19,2; range 13-77 years). ORTs were found in 30 eyes of 15 patients (15/18; 83,3% of the patients). We identified 3 en face OCT patterns: round lesions with scalloped boundaries which involved the peripapillary area with more or less evident pseudodendritic ORTs (PD-ORT) (pattern p; 26,7%); central islands with PD-ORTs (pattern i; 53,3%); residual outer retinal areas with no ORTs (pattern r; 20,0%).Conclusions: In CHM, en face OCT imaging allows us to observe various morphological features of the ORTs in different stages of disease, not detectable with other imaging techniques. ORTs were not identified in the mildest phenotypes. En face OCT is a non-invasive useful tool in the characterization and monitoring of the disease.

Optical Coherence Tomography Angiography Imaging in Inherited Retinal Diseases

Optical coherence tomography angiography (OCTA) is a novel, noninvasive imaging modality that allows depth-resolved imaging of the microvasculature in the retina and the choroid. It is a powerful research tool to study the pathobiology of retinal diseases, including inherited retinal dystrophies. In this review, we provide an overview of the evolution of OCTA technology, compare the specifications of various OCTA devices, and summarize key findings from published OCTA studies in inherited retinal dystrophies including retinitis pigmentosa, Stargardt disease, Best vitelliform macular dystrophy, and choroideremia. OCTA imaging has provided new data on characteristics of these conditions and has contributed to a deeper understanding of inherited retinal disease.

Cone Structure Persists Beyond Margins of Short-Wavelength Autofluorescence in Choroideremia

Purpose

We studied the relationship between structure and function of the choriocapillaris (CC), retinal pigment epithelium (RPE), and photoreceptors in patients with choroideremia (CHM).

Methods

Six CHM patients (12 eyes) and four normal subjects (six eyes) were studied with fundus-guided microperimetry, confocal and nonconfocal adaptive optics scanning laser ophthalmoscopy (AOSLO), near-infrared and color fundus photos, short wavelength fundus autofluorescence (SW-AF), and swept-source optical coherence tomography (SS-OCT) and angiography (SS-OCTA) images. Cone spacing was represented using Z-scores (standard deviations from the mean at that eccentricity). CC flow voids were defined using a threshold of 1 SD below the normal mean.

Results

Cone spacing Z-scores were not significantly correlated with distance from the borders of preserved RPE, determined using either the SS-OCT or SW-AF scans. Cone spacing Z-scores were significantly correlated with CC flow voids and retinal sensitivity. Flow voids were abnormal in regions of preserved RPE and increased progressively from within -2° of the preserved area to +2° beyond the border. Visual sensitivity decreased as CC flow voids increased approaching and beyond the border of preserved structure.

Conclusions

In CHM, cone spacing Z-scores correlated with CC flow voids, and were negatively correlated with retinal sensitivity, suggesting cone degeneration accompanied reduced CC perfusion. Functional cones were found outside the presumed borders of preserved outer-retina/RPE as defined by SW-AF, but not outside the borders determined by SS-OCT. The use of SW-AF to identify the border of preserved structures may underestimate regions with cells that may be amenable to treatment.