Cone Contrast and Entropy of Adaptive Optics Images in Choroideremia

Choroideremia (CHM) is an X-linked inherited retinal degeneration that results in the progressive loss of photoreceptors, retinal pigment epithelium, and choroid. The present study examines the contrast and entropy of cone intensities in CHM and control images using adaptive optics scanning light ophthalmoscopy and texture analysis.

Thirteen patients with CHM and twelve normal-sighted controls were imaged using a custom-built, multi-modal adaptive optics scanning light ophthalmoscope (AOSLO). AOSLO images were registered and montaged and regions of interest located at 0.5°, 1°, 2°, and 4° were cropped for each participant. Cones were identified in each region of interest, and a gray level co-occurrence matrix (GLCM) was created for each image and each cone location. Image and cone contrast and entropy were calculated from each GLCM. An unbalanced two-way analysis of variance and Bonferroni post hoc test was conducted over disease group and retinal eccentricity for both contrast and entropy, where p < 0.05 was considered significant.

Cone density was decreased in CHM compared to control at all eccentricities (p < 0.01), while cone nearest neighbor distance was increased in CHM (p < 0.01). Cone contrast and entropy was decreased in CHM compared to control both when analyzing the full image of the cone mosaic and when performing the analysis for individual cones (p < 0.001 for all).

Cone contrast and entropy textural analyses may provide a biomarker of cone health in retinal disease and its response to treatment.Funding for the study provided by NIH R01EY028601, NIH P30EY001583, Research to Prevent Blindness, Center for Advanced Retinal and Ocular Therapeutics, and the F. M. Kirby Foundation.