Structural and Functional Characteristics of Color Vision Changes in Choroideremia

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.

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.

Alterations of color vision and pupillary light responses in age-related macular degeneration

Introduction

Age-related macular degeneration (AMD) is the leading cause of irreversible central vision loss in developed countries and one of the leading causes of blindness. In this work, we evaluated color vision and the pupil light reflex (PLR) to assess visual function in patients with early and neovascular AMD (NVAMD) compared with the control group.

Methods

We recruited 34 early patients with dry AMD and classified them into two groups following AREDS: 13 patients with NVAMD and 24 healthy controls. Controls and patients with early dry AMD had visual acuity (VA) best or equal to 20/25 (0.098 logMAR). Color vision was assessed in controls and patients with early dry AMD using the Cambridge Color Test (CCT) 2.0 through the Trivector protocol. The PLR was evaluated using a Ganzfeld, controlled by the RETI-port system. The stimuli consisted of 1s blue (470 nm) and red (631 nm) light flashes presented alternately at 2-min intervals. To assess the cone contribution, we used a red flash at 2.4 log cd.m^-2, with a blue background at 0.78 log cd.m^-2. For rods, we used 470-nm flashes at -3 log cd.m^-2, and for the melanopsin function of ipRGCs, we used 470 nm at 2.4 log cd.m^-2.

Results

Patients with early dry AMD had reduced color discrimination in all three axes: protan (p = 0.0087), deutan (p = 0.0180), and tritan (p = 0.0095) when compared with the control group. The PLR has also been affected in patients with early dry AMD and patients with NVAMD. The amplitude for the melanopsin-driven response was smaller in patients with early dry AMD (p = 0.0485) and NVAMD (p = 0.0035) than in the control group. The melanopsin function was lower in patients with NVAMD (p = 0.0290) than the control group. For the rod-driven response, the latency was lower in the NVAMD group (p = 0.0041) than in the control group. No changes were found in cone-driven responses between the control and AMD groups.

Conclusion

Patients with early dry AMD present diffusely acquired color vision alteration detected by CCT. Rods and melanopsin contributions for PLR are affected in NVAMD. The CCT and the PLR may be considered sensitive tests to evaluate and monitor functional changes in patients with AMD.

Optimal Learning Samples for Two-Constant Kubelka-Munk Theory to Match the Color of Pre-colored Fiber Blends

Due to the dyeing process, learning samples used for color prediction of pre-colored fiber blends should be re-prepared once the batches of the fiber change. The preparation of the sample is time-consuming and leads to manpower and material waste. The two-constant Kubelka-Munk theory is selected in this article to investigate the feasibility to minimize and optimize the learning samples for the theory since it has the highest prediction accuracy and moderate learning sample size requirement among all the color prediction models. Results show that two samples, namely, a masstone obtained by 100% pre-colored fiber and a tint mixed by 40% pre-colored fiber and 60% white fiber, are enough to determine the absorption and scattering coefficients of a pre-colored fiber. In addition, the optimal sample for the single-constant Kubelka-Munk theory is also explored.