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Nancy J Coletta, Rhett Stroupe; Asymmetry in Foveal Pit Dimensions. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5274.
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© ARVO (1962-2015); The Authors (2016-present)
Myopic eyes generally have shallower foveal pits than emmetropic eyes, and we have reported that the width of the foveal pit decreases with increasing axial length or increasing myopia (Stroupe and Coletta, ARVO, 2013). The foveal pit exhibits an asymmetry, in that it is wider in the horizontal than in the vertical dimension. The purpose of this study was to examine how the asymmetry in foveal pit dimension varies with axial length.
Axial lengths and macular thickness were obtained on both eyes of 25 subjects (average age 24.8 years). Refractions ranged from plano to -9.90 D. Axial lengths were measured with a Zeiss IOL Master and retinal thickness was measured with an Optovue RTVue spectral domain OCT. We used the MM6 scan that consists of twelve 6-mm length B-scans that rotate through the fovea at 15 deg intervals. OCT results were analyzed using a custom Matlab program that computed these parameters for each scan orientation: maximum thickness on either side of the foveal pit, minimum thickness, depth of the foveal pit, pit width across the maximum thickness (FWFM) and pit width at half the pit depth (FWHM). Lateral dimensions were corrected for the variation in transverse magnification of the OCT scan against axial length. Results from the vertical scan and its two adjacent scan orientations were averaged to obtain vertical dimensions and results from the horizontal scan and its two adjacent scan orientations were averaged to obtain horizontal dimensions.
Refraction was correlated with axial length (p<0.001). Average foveal dimensions in the vertical and horizontal meridians, respectively, were: pit depth, 134.6 and 128.5 micron; maximum thickness, 345.7 and 338.6 micron; FWFM, 2135.0 and 2372.6 micron; FWHM, 820.0 and 883.3 micron (all p<0.001 in paired t-tests). The fovea was thus wider horizontally by a factor of 1.11 at the maximum thickness and by 1.08 at half the pit depth. At the maximum thickness, the asymmetry in pit dimensions did not correlate with axial length, but the vertical/horizontal ratio of FWHM pit width significantly decreased with axial length (p=0.04).
The foveal pit is wider horizontally than vertically and the foveal pit depth is greater vertically. These asymmetries may be related to the greater retinal thickness in the vertical meridian due to the presence of the nerve fiber bundles. Alterations in the foveal pit morphology in axially myopic eyes may be associated with retinal stretching.
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