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Ann E Elsner, Christopher Anderson Clark, Toco Yuen Ping Chui, Joel A Papay, Benjamin J Konynenbelt, Stephen A Burns; Macular Topography and Foveal Specialization in Young Healthy Subjects. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2628.
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© ARVO (1962-2015); The Authors (2016-present)
To provide a quantitative model of macular topography that incorporates the degree of foveal specialization, thereby improving the detection of retinal disease, myopia progression, developmental differences, or success of treatment. We and others have measured, using adaptive optics, large individual differences in cone distribution for age, eye length, and birth month. If individual differences in retinal thickness mirror those in cone distribution, then thickness in the central macula does not scale with thickness at greater eccentricities. Instead the migration of cones centrally that provides foveal specialization would lead to fewer cones more eccentrically and a thinner retina outside the central macula. Alternatively, retinal thickness in the central macula could be dominated by other factors, such as a larger number of rods or other neurons in some eyes, so that some retinas would be overall thick and others thin.
Subjects aged 18 - 35 yr with a normal fundus and spherical error from + 1 D to -3D were imaged with SD-OCT (Spectralis, Heidelberg). From horizontal and vertical scans through the fovea, macular thickness was measured with custom software (Matlab, Mathworks). The total retinal thickness (TRT), from the inner limiting membrane to the outer edge of the retinal pigment epithelium, was quantified at 2 and 7 deg nasal, temporal, inferior, and superior. The outer nuclear + Henle fiber layer (ONL) was measured at the same locations. Linear regressions were performed on the ratio of the TRT at 7 and 2 deg compared with TRT at 2 deg, and similarly for ONL. Linear regressions were also performed for 7 deg vs. 2 deg for TRT and for ONL.
Macular thickness, both TRT and ONL, was uncorrelated for 2 vs 7 deg at all meridians. Instead, the ratio of retinal thickness at 7 and 2 deg was correlated with retinal thickness at 2 deg for both TRT and ONL and for all 4 meridians, p < 0.001. The correlations were negative, i.e. thicker central macula was associated with thinner retina at more eccentric locations.
Retinal thickness, like cone density, is not characterized by a scalar factor that is consistent across eccentricity but varies across individuals. The results support a model in which cones from outside the fovea migrate centrally to provide foveal specialization, and this strongly influences retinal thickness for the entire retina and the ONL.
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