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Jenna Cava, Rebecca Mastey, Mitchell Allphin, Robert F Cooper, Joseph Carroll; Assessing interocular symmetry of foveal cone density. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4578. doi: https://doi.org/.
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The contralateral eye often serves as a control for the experimental “study eye,” a practice that assumes interocular symmetry of the feature(s) being analyzed. Due to their small size, foveal cones have eluded routine adaptive optics (AO) imaging—creating a lack of data on symmetry of foveal cone topography in normal eyes (though there have been studies of the parafoveal mosaic). We examined interocular symmetry of peak foveal cone density using AO scanning light ophthalmoscopy (AOSLO) in a cohort with normal vision.
We acquired AOSLO images of the central macula in each eye of 37 subjects with normal vision (age range: 12-64 years; 13 M, 24 F). Steps to improve image quality at the foveola included using a sub-airy disc pinhole,1 680nm imaging wavelength,2 a small field of view (0.5° or 0.75°), and time or through-focus averaging. Axial length was measured in each eye to derive the lateral scale of the AOSLO images. Processed images were montaged, from which we extracted a 300x300 µm region of interest (ROI) centered on the estimated location of highest cone packing. Cones in each ROI were identified using a semi-automated algorithm. Density maps were created with a sum map approach, using a sliding square window that changed size to contain 100 bound cells and estimate bound cell density at each coordinate. Peak cone density (PCD) was extracted from each map and fellow eye densities were compared with a paired t-test.
Of 37 subjects, the foveal cone mosaic was resolvable in both eyes of 30 subjects, one eye of 2 subjects, and neither eye of 5 subjects. PCD varied widely across subjects, ranging from 122,710 cones/mm2 to 247,710 cones/mm2. Average PCD (± SD) for right eyes was 181,249 ± 27,463 cones/mm2 (n = 32) and for left eyes was 181,219 ± 28,396 cones/mm2 (n = 30). Data from right and left eyes passed the D’Agostino and Pearson normality test (p = 0.96, p= 0.88, respectively). PCD of fellow eyes were not significantly different (t = 0.143, df = 29, p = 0.89).
There is a high-degree of interocular symmetry of peak foveal cone density in subjects with normal vision. This agrees with previous AOSLO data on the parafoveal cone mosaic as well as OCT-derived estimates of foveal ONL thickness. Whether these findings extend to individuals with inherited retinal degenerations is not known, but our data provide the “normal” degree of symmetry.1Sredar, PMID: 296292392Putnam, PMID: 21164835
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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