Scotopic microperimetry: evolution, applications and future directions

DRUSEN VOLUME AS CLINICAL OUTCOME MEASURE IN SUBJECTS WITH MALATTIA LEVENTINESE

PURPOSE

To assess if drusen volume can serve as structural clinical outcome marker in Malattia Leventinese, and to evaluate whether cones or rods are more affected by its progression, using multimodal imaging and mesopic and two-color scotopic microperimetry.

METHODS

This was a prospective monocentric cross-sectional cohort study of participants with genetically confirmed Malattia Leventinese. Participants were classified according to morphology. Mean drusen volume, calculated from spectral-domain optical coherence tomography, was compared with microperimetry parameters (mesopic retinal sensitivity, scotopic red and cyan function, difference between scotopic cyan-red function).

RESULTS

Fourteen participants (28 eyes) were enrolled. Mean drusen volume increased (bilaterally P = 0.028) and mesopic retinal sensitivity decreased with later stage (right eye: P = 0.028; left eye: P = 0.050). Scotopic microperimetry showed that scotopic cyan function was lower than scotopic red function in moderate stage. Scotopic red function decreased in severe stage. Mean drusen volume correlated to mesopic retinal sensitivity (right eye: P < 0.001; left eye: P = 0.007).

CONCLUSION

Retinal sensitivity diminishes with Malattia Leventinese progression. Rod function declines before cone function, whereas at late stages, cone loss predominates. Drusen accumulation, initially speckled around the macula and optic disc and confluent with disease progression, correlates well with visual function loss and impaired quality of life. Thus, therapeutically reducing drusen accumulation could be efficacious.

Anti-TRPM1 autoantibody-positive unilateral melanoma associated retinopathy (MAR) triggered by immunotherapy recapitulates functional and structural details of TRPM1-associated congenital stationary night blindness

Purpose

To describe the retinal phenotype of an unusual case of anti-TRPM1 autoantibody-positive unilateral melanoma-associated retinopathy (MAR) triggered by nivolumab therapy and compare with the phenotype of TRPM1-associated Congenital Stationary Night Blindness (TRPM1-CSNB).

Observations

Unilateral MAR was diagnosed 3 months after starting nivolumab therapy for consolidation of a successfully treated melanoma. Retinal autoantibodies against TRPM1 were identified. ffERG, microperimetry and static chromatic perimetry confirmed unilateral ON-Bipolar Cell (ON-BPC) dysfunction and central rod sensitivity losses in the left eye; the contralateral eye was normal. There was borderline ganglion cell (GCL) and inner nuclear layer (INL) thinning, but a significantly thinner inner plexiform layer (IPL) in the affected compared to the unaffected eye. Longitudinal reflectivity profiles (LRPs) demonstrated an abnormal inner plexiform layer (IPL) lamination in the involved eye. Nearly identical changes were documented in two cases of TRMP1-cCSNB and in a case of anti-TRPM1 autoantibody-negative MAR. The functional changes partially recovered with discontinuation of the medication without added immunosuppression.

Conclusions and Importance

Comparisons between the affected and unaffected eye in this unilateral MAR case revealed inner retinal abnormalities and abnormal lamination of the IPL associated with the classical retina-wide ON-BPC dysfunction, and localized central rod-mediated sensitivity losses. A nearly identical structural phenotype in two cases of cCSNB and a case of anti-TRPM1 autoantibody-negative MAR supports a specific structural-functional phenotype for these conditions with ON-BPC dysfunction.

Exploring Scotopic Microperimetry as an Outcome Measure in Choroideremia

Purpose

Choroideremia is an X-linked outer retinal degeneration. Early symptoms include nyctalopia and progressive visual field loss, but visual acuity is preserved until late disease stages. Dark-adapted two-color fundus-controlled perimetry (also known as scotopic microperimetry) has been developed to enable spatial assessment of rod and cone photoreceptor function. This study explores the use of scotopic microperimetry in patients with choroideremia.

Methods

Twenty patients with choroideremia and 21 age-matched healthy controls completed visual acuity and scotopic microperimetry testing, which used the Scotopic Macular Integrity Assessment (S-MAIA) microperimeter. A subset of participants completed repeat scotopic testing to enable Bland-Altman repeatability analyses. Test reliability was assessed using fixation stability, fixation losses, and assessment of the rod-free zones. Pointwise sensitivity, mean sensitivity, and volume sensitivity indices were analyzed.

Results

False positive responses were the main source of poor test reliability, indicated by stimuli responses in the physiological blind spot and lack of rod-free mapping. Scotopic cyan and red sensitivities were significantly reduced in choroideremia participants (n = 17) compared to healthy controls (n = 16) (P < 0.01, Mann-Whitney U test). Scotopic cyan sensitivity was statistically lower than scotopic red sensitivity in both healthy controls and choroideremia (P < 0.01, Wilcoxon signed rank test). Interpretation of scotopic cyan-red differences should be used with caution due to high test-retest variability.

Conclusions

Scotopic microperimetry could be a useful outcome measure in patients with early choroideremia. Careful selection of test grid design and sensitivity indices is required.

Translational Relevance

Scotopic microperimetry may be a useful outcome measure in clinical trials for patients with early stage choroideremia.

Retinal sensitivity changes in early/intermediate AMD: a systematic review and meta-analysis of visual field testing under mesopic and scotopic lighting

Visual fields under mesopic and scotopic lighting are increasingly being used for macular functional assessment. This review evaluates its statistical significance and clinical relevance, and the optimal testing protocol for early/intermediate age-related macular degeneration (AMD). PubMed and Embase were searched from inception to 14/05/2022. All quality assessments were performed according to GRADE guidelines. The primary outcome was global mean sensitivity (MS), further meta-analysed by: AMD classification scheme, device, test pattern, mesopic/scotopic lighting, stimuli size/chromaticity, pupil dilation, testing radius (area), background luminance, adaptation time, AMD severity, reticular pseudodrusen presence, and follow-up visit. From 1489 studies screened, 42 observational study results contributed to the primary meta-analysis. Supported by moderate GRADE certainty of the evidence, global MS was significantly reduced across all devices under mesopic and scotopic lighting with large effect size (-0.9 [-1.04, -0.75] Hedge's g, P < 0.0001). The device (P < 0.01) and lighting (P < 0.05) used were the only modifiable factors affecting global MS, whereby the mesopic MP-1 and MAIA produced the largest effect sizes and exceeded test-retest variabilities. Global MS was significantly affected by AMD severity (intermediate versus early AMD; -0.58 [-0.88, -0.29] Hedge's g or -2.55 [3.62, -1.47] MAIA-dB) and at follow-up visit (versus baseline; -0.62 [-0.84, -0.41] Hedge's g or -1.61[-2.69, -0.54] MAIA-dB). Magnitudes of retinal sensitivity changes in early/intermediate AMD are clinically relevant for the MP-1 and MAIA devices under mesopic lighting within the central 10° radius. Other factors including pupil dilation and dark adaptation did not significantly affect global MS in early/intermediate AMD.

Hypomorphic CDHR1 variants may result in retinitis pigmentosa with relative preservation of cone function

PURPOSE

Retinitis pigmentosa (RP) associated with biallelic variants in CDHR1 has rarely been reported, and detailed phenotyping data are not available. RP implies relative preservation of foveal cones, when compared to cone-rod dystrophy associated with biallelic null variants in CDHR1. We hypothesize that RP may occur in association with one or more hypomorphic CDHR1 alleles.

MATERIALS AND METHODS

Retrospective report of a 48-year-old patient with CDHR1-associated RP with a hypomorphic missense variant c.562 G>A, p. (Gly188Ser) and a novel, unreported variant affecting a canonical splice acceptor site (c.784-1 G>C). Clinical examination, multimodal retinal imaging, electroretinography, visual field testing, and mesopic microperimetry were undertaken 8 years apart. Scotopic microperimetry was also performed. The DNA sequence context of the variants was examined to identify theoretical CRISPR-Cas9 base-editing strategies.

RESULTS

The patient presented at 35 years with a 12-year history of nyctalopia. His best corrected visual acuity was 20/20. Clinical presentation, multimodal retinal imaging studies, electroretinography, and mesopic microperimetry were typical of a progressive rod-cone dystrophy (i.e. classic RP). There were no scotomas within the central field as would be expected at this age in CDHR1-associated cone-rod dystrophy. Scotopic microperimetry suggested some preservation of macular cone over rod function, although both were severely impaired. A suitable CRISPR adenine base editor was identified that could theoretically correct the missense variant c.562 G>A, p. (Gly188Ser).

CONCLUSIONS

CDHR1-associated RP shows a relative preservation of cone function in the presence of a presumed hypomorphic allele and may be considered a hypomorphic disease phenotype. Further work is required to identify modifying factors that determine disease phenotype since macular dystrophy, with relative sparing of rods, may also occur with hypomorphic CDHR1 alleles.

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.

Choroideremia: Toward Regulatory Approval of Retinal Gene Therapy

Choroideremia is an X-linked inherited retinal degeneration characterized by primary centripetal degeneration of the retinal pigment epithelium (RPE), with secondary degeneration of the choroid and retina. Affected individuals experience reduced night vision in early adulthood with blindness in late middle age. The underlying CHM gene encodes REP1, a protein involved in the prenylation of Rab GTPases essential for intracellular vesicle trafficking. Adeno-associated viral gene therapy has demonstrated some benefit in clinical trials for choroideremia. However, challenges remain in gaining regulatory approval. Choroideremia is slowly progressive, which presents difficulties in demonstrating benefit over short pivotal clinical trials that usually run for 1-2 years. Improvements in visual acuity are particularly challenging due to the initial negative effects of surgical detachment of the fovea. Despite these challenges, great progress toward a treatment has been made since choroideremia was first described in 1872.

A cross-sectional study to assess the clinical utility of modern visual function assessments in patients with inherited retinal disease: a mixed methods observational study protocol

BACKGROUND

Treatment options for patients with inherited retinal disease are limited, although research into novel therapies is underway. To ensure the success of future clinical trials, appropriate visual function outcome measures that can assess changes resulting from therapeutic interventions are urgently required. Rod-cone degenerations are the most common type of inherited retinal disease. Visual acuity is a standard measure but is typically preserved until late disease stages, frequently making it an unsuitable visual function marker. Alternative measures are required. This study investigates the clinical utility of a range of carefully selected visual function tests and patient reported outcome measures. The aim is to identify suitable outcome measures for future clinical trials that could be considered for regulatory approval.

METHODS

This cross-sectional study involves two participant groups, patients with inherited retinal disease (n = 40) and healthy controls (n = 40). The study has been designed to be flexible and run alongside NHS clinics. The study is split into two parts. Part one includes examining standard visual acuity, low luminance visual acuity, the Moorfields acuity chart visual acuity, mesopic microperimetry and three separate patient reported outcome measures. Part two involves 20 min of dark adaptation followed by two-colour scotopic microperimetry. Repeat testing will be undertaken where possible to enable repeatability analyses. A subset of patients with inherited retinal disease will be invited to participate in a semi-structured interview to gain awareness of participants' thoughts and feelings around the study and different study tests.

DISCUSSION

The study highlights a need for reliable and sensitive validated visual function measures that can be used in future clinical trials. This work will build on work from other studies and be used to inform an outcome measure framework for rod-cone degenerations. The study is in keeping with the United Kingdom Department of Health and Social Care research initiatives and strategies for increasing research opportunities for NHS patients as part of their NHS care.

TRIAL REGISTRATION

ISRCTN registry, ISRCTN24016133, Visual Function in Retinal Degeneration, registered on 18th August 2022.

Assessment of Scotopic Function in Rod-Cone Inherited Retinal Degeneration With the Scotopic Macular Integrity Assessment

Purpose

The scotopic macular integrity assessment (S-MAIA) can perform scotopic assessment to detect localized changes to scotopic rod and cone function. This study is an exploratory investigation of the feasibility of using the S-MAIA in a rod-cone dystrophy population to identify the pattern of loss in scotopic photoreceptor function.

Methods

Twenty patients diagnosed with a rod-cone dystrophy underwent visual acuity testing, full-field stimulus threshold assessment, and multiple S-MAIA tests after dark adaptation periods of 20 minutes and 45 minutes performed separately. Only right eyes were tested. Three tests were performed following a learning test. A Bland-Altman analysis was used to assess repeatability and agreement between tests after the two time periods. Spatial interpolation maps were created from the group plots to display the pattern of rod and cone loss.

Results

Learning effects took place between testing sessions 1 and 2 but not 2 and 3. Limits of agreement were larger in the patient eyes than control eyes, but within previously reported values. Using longer adaptation time of 45 minutes did not offer a significant advantage over 20 minutes. Patterns for the cyan and red sensitivities were different, indicating different patterns of loss for rods and cones.

Conclusions

A dark adaptation time of 20 minutes before testing is sufficient for thresholding. The S-MAIA is suitable for use in patients with a logarithm of the minimum angle of resolution vision of at least 0.7 and provides a viable outcome measure for patients with rod-cone dystrophies and preserved central vision. The spatial information about scotopic function from the S-MAIA provides information about disease processes and progression.

Translational Relevance

There is a need for scotopic measures for use in clinical trials. Scotopic microperimetry works well in patients with early disease, allowing the extension of recruitment criteria for novel therapies of rod-cone dystrophies.