Abstract
Purpose :
To assess the relationship between anatomical foveal specializations in the human retina.
Methods :
AOSLO and OCT images from 45 participants with no known ophthalmic pathology were obtained with the age of participants ranging from 12 to 64 years (30 female, 15 male). Cirrus OCT line scans were segmented using ImageJ to determine boundaries for retinal layers. Across the OCT B-scans, outer nuclear layer (ONL) thickness was defined as the difference between the Henle Fiber Layer/ONL boundary and the external limiting membrane (ELM). Foveal and parafoveal AOSLO images were acquired, processed, and montaged – from which a region of interest centered on the approximate location of peak cone density was cropped. Cones were semi-automatically identified and cone density maps were generated to extract estimates of peak cone density and total cone numerosity. Topographical maps of retinal thickness derived from OCT macular volumes were used to calculate foveal pit metrics using previously published algorithms. Statistical analyses were performed to assess the relationship between ONL thickness and peak cone density, as well as the relationships between other foveal specializations.
Results :
The median ONL thickness among participants was 104.29 μm, ranging from 78.09 to 131.74 μm. Peak cone density ranged from 132,410 to 241,286 cones/mm2, with a median of 185,539 cones/mm2. Median pit diameter was 1.92 mm ranging from 1.48 to 2.64 mm, while median pit volume was 0.09 mm3 ranging from 0.03 to 0.19 mm3. There was no significant correlation between maximum ONL thickness at the fovea and peak cone density (r = 0.27, P = 0.0771). Pit diameter (r = -0.52, P = 0.0002) and pit volume (r = -0.360, P = 0.0151) were both negatively correlated with peak cone density.
Conclusions :
Maximum ONL thickness should be used with caution as a biomarker for assessing remnant foveal cone structure. To accurately monitor progression in cone degenerative diseases the use of AOSLO and OCT should be considered. Similar multimodal approaches may be beneficial for evaluating the success of interventions aimed at slowing cone degeneration. The correlation between pit size and peak cone density supports a mechanistic developmental link between these anatomical specializations, at least in individuals with normal vision.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.