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Amitabha S. Bhakta, Nripun Sredar, Tyler W. Wyatt, Kevin M. Ivers, Hope M. Queener, Nimesh B. Patel, Jason Porter; Examining The Relative Locations Of Foveal Parameters Using High-resolution In Vivo Imaging. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4112.
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© ARVO (1962-2015); The Authors (2016-present)
The foveal center is often used as a reference point for specifying retinal location. However, considerable variation exists in the structural characteristics of the fovea within normal eyes. We examined the relationship between the locations of the foveal pit center, peak total photoreceptor length, peak photoreceptor outer segment (OS) length and estimated peak cone density calculated from in vivo images.
Spectral domain optical coherence tomography (SDOCT) [Spectralis HRA+OCT] cross-sectional volume scans (15° x 5°, 131 B-scans) were acquired with Enhanced Depth Imaging across the foveal pit in right eyes of 11 normal Caucasian subjects (mean age: 27.4 ± 5.7 years). Inner and outer retinal layers were manually delineated using Spectralis software and a custom MATLAB program. Total photoreceptor (inner + outer segment) and OS thickness profiles were calculated. The center of a 2 dimensional Gaussian fit to each profile was taken to be the location of peak total photoreceptor and OS thicknesses. The total retinal thickness profile was also calculated and used to determine the location of the foveal pit center (taken as the mean location of the centers of the ellipse fit to locations of equal retinal thickness within the foveal rim). High-resolution images of the cone mosaic were acquired throughout the foveal region in 5 of these eyes using an adaptive optics scanning laser ophthalmoscope (AOSLO). Due to our inability to image the smallest foveal cones (< ~0.3º), locations of peak cone photoreceptor density were estimated based on surrounding regions of resolvable cones (Putnam et al. J. Vis. 2005; 5: 632-639) and were compared with the aforementioned locations determined from SDOCT images.
Photoreceptor inner segment length was relatively constant throughout the foveal region in each eye. The locations of peak OS and peak total photoreceptor thicknesses were located closely (mean separation = 10.9 ± 5.2 µm). The mean separations between the foveal pit center and locations of peak total photoreceptor thickness and peak OS thickness were 50.87 ± 29.3 µm and 55.04 ± 25.7 µm, respectively. The estimated location of peak cone density was separated from the foveal pit center and location of peak total photoreceptor length by an average of 36.2 ± 25 µm and 62.01 ± 8.6 µm, respectively.
The locations of the foveal pit center, peak total photoreceptor thickness, peak OS thickness and estimated peak cone density did not coincide. Being able to resolve the smallest foveal cones (~0.3º) could improve understanding of the relative location of peak cone density with respect to the SDOCT-derived foveal features.
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