Abstract
Purpose :
Choroideremia (CHM) is an X-linked inherited retinal degeneration causing loss of photoreceptors, retinal pigment epithelium and choriocapillaris that affects 1 in 50,000 individuals. Studies have revealed abnormalities in cone photoreceptor metrics within the retained island of functioning retina in CHM and a sharp decline in visual sensitivity at the atrophic border. Here we describe the relationship between cone density and visual sensitivity within the retained central island in CHM.
Methods :
The cone mosaics of thirty patients aged 10-57 years with CHM were imaged using a multi-modal, custom-built adaptive optics scanning light ophthalmoscope (AOSLO). Images were desinusoided, registered and automatically montaged with manual correction. A Nidek MP-1 microperimeter was used to measure retinal sensitivity to a Goldman III white stimulus presented for 200ms on a dark background at locations every 1.5° from the fovea to 12° along meridians at 0°, 90°, 180° and 360°. Locations corresponding to sensitivity measurements were identified by aligning the locus of fixation between microperimetry and AOSLO. 70 x 70 micron regions of interest (ROIs) were selected from these locations. Cones were identified and bound cone density was calculated for each ROI. ROIs were binned by eccentricity and cone density was compared to sensitivity at each eccentricity using linear regression. Cone density and sensitivities were compared to previously published data for healthy controls using unpaired t-tests.
Results :
314 individual ROIs were analyzed. Cone density was significantly decreased compared to healthy controls at all eccentricities measured (p<0.0002). Microperimetry sensitivities were reduced in CHM compared to healthy controls in all quadrants (p<0.0001). There was a statistically significant correlation between cone density and visual sensitivity at the locus of fixation (p=0.0005) and at 400 and 800 µm from the fovea (p<0.0001, p=0.0004, respectively), but not at 1200, 1600 or 2000 µm (p=0.3567, p=0.4153 and p=0.7690 respectively).
Conclusions :
The correlation between cone density and retinal sensitivity within 1 mm of the foveal center in CHM suggests central sensitivity loss is driven by photoreceptor loss. These findings provide support for the use of structural outcome measures in clinical trials assessing novel therapeutics in CHM, as preserving cone structure would be expected to preserve cone function in this disease.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.