Abstract
Purpose :
There exist no reports comparing the cone spectral types between fellow eyes of the same individual. Here, we sought to address this gap and test whether the combination of genetic and developmental factors common to the fellow eyes of an individual impose similar cone spectral compositions between them.
Methods :
Line-scan AO-OCT was used to image both eyes of two subjects from 0.4 to 10° temporal eccentricity. After 1-3 min of dark adaptation, OCT volumes were recorded to measure the response of individual cones to a 660±10 nm bleach. The volume rate was 20-25 Hz and the field of view ranged from 1-1.6°. Volumes were processed to obtain changes in optical path length (ΔOPL) in the cone outer segment and the spectral type was assigned to each cone based on the differential ΔOPL caused by the 660 nm bleach. The ΔOPL in each cone type, L:M cone ratio, proportion and density of S-cones were compared between both eyes.
Results :
In all, 14408 cones (OS: 5607, OD: 8801) and 10253 cones (OS: 4033, OD: 6620) were classified with high accuracy in subject 1 (S1) and S2 respectively. The mean difference of saturated ΔOPL between eyes for L, M and S-cones was insignificant; 67.3 ± 3.3, 16.3 ± 3, 4.7 ± 5 nm for S1 and 14.7 ± 5.9, 8.6 ± 2.1, 5.2 ± 2.2 nm for S2. The proportion of S-cones increased with eccentricity from 0.4° to 10° in both eyes of S1 (2.3 to 7.7%) and S2 (2.7 to 9.9%). The maximum S-cone density was observed between 0.6° and 0.9° for both eyes in each subject. The proportions and the eccentricity of maximum S-cone density did not differ significantly between fellow eyes. The L:M cone ratio remained relatively similar between fellow eyes as a function of eccentricity. Between 1.5 - 10 deg, the L:M cone ratio in S1 ranged from 1.7 to 3 (LM ratio in OS = 2.2 ± 0.5, OD = 2.3 ± 0.4). In S2, the range was 1.3 to 2.1 (OS= 1.6 ± 0.2, OD= 1.6 ± 0.3). A decreasing trend of L:M cone ratio was observed at eccentricities less than 1° in both eyes of each subject.
Conclusions :
No significant differences were observed in the cone spectral composition or the magnitude of the light evoked ΔOPL response in the different cone types between fellow eyes. While this represents a coarse-grained analysis in terms of L:M cone ratio, and % S-cones vs. eccentricity, finer measures of local structure will be required to reveal subtle differences and symmetries, if any, in spectral topography between the fellow eyes.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.