Interocular symmetry of foveal cone topography in achromatopsia (ACHM)

Abstract

Purpose : Interocular symmetry of foveal cone structure in ACHM has received little attention, despite significant variation across patients.[1] The variability between eyes may be important for selection of patients and monitoring outcomes in clinical trials. Here, we assess interocular symmetry of foveal cone topography in ACHM using non-confocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO).

Methods : Split-detection AOSLO images of the foveal cone mosaic were acquired from both eyes of subjects with CNGA3- or CNGB3-associated ACHM (n = 4 and 16, respectively). Cones were identified manually or semi-automatically[2] within a manually-delineated rod-free zone.[1] Peak cone density was determined using a 55 x 55 µm sampling window. Inter-cell distance (ICD) between a cell and its immediate neighbors was calculated for each cell in the rod-free zone. The mean and standard deviation (SD) of ICD for each mosaic was calculated to derive the coefficient of variation (CV).

Results : Representative images of remnant cone structure in both eyes of subjects with CNGA3- and CNGB3-associated ACHM are shown (Figure). Peak cone density (mean ± SD: 19,868 ± 12,259 and 18,744 ± 11,508 cones/mm² for OD and OS, respectively) was similar between eyes with ACHM (p = 0.35, Wilcoxon test). ICD (mean ± SD: 12.98 ± 4.37 µm for OD and 12.76 ± 4.04 µm for OS) was not different between eyes with ACHM (p = 0.57, paired t-test). CV values (mean ± SD: 0.28 ± 0.05 for OD and 0.26 ± 0.06 for OS) demonstrate similar mosaic topography between eyes (p = 0.29, paired t-test).

Conclusions : These results demonstrate high interocular symmetry of the foveal cone mosaic (density and packing) in ACHM. This is consistent with data showing high interocular symmetry of foveal outer nuclear layer thickness in ACHM.[3] The results are of potential value in longitudinal monitoring of patients during treatment trials and further suggest that both eyes of a given subject may have similar therapeutic potential.

[1] PMID: 27479814
[2] PMID: 27231641
[3] 2017 ARVO E-Abstract 6005

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Figure. Remnant foveal cone structure in ACHM. In a subject with CNGA3-associated ACHM (top), peak cone density OD is 9,917 cones/mm² and OS is 9,917 cones/mm². In a subject with CNGB3-associated ACHM (bottom), peak cone density OD is 13,223 cones/mm² and OS is 12,893 cones/mm².