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Christopher Anderson Clark, Ann E Elsner, Casey Carr, Theodore Chow; Differences in INL/ONL Ratios for Myopes and Emmetropes/Hyperopes. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5638.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal thickness has been shown to differ between myopes and emmetropes, with myopes typically having relatively thinner retinas outside of 5 degrees from the fovea, and, in some studies, myopes haveing thicker retinas at the fovea. The Inner Nuclear Layer (INL), composed primarily of bipolar, horizontal, and amacrine cell nuclei, and the Outer Nuclear Layer (ONL), composed of photoreceptor nuclei and Mueller cell processes, may contain some of the first signalling neurons in the emmetropization cascade. The purpose of this study is examine change in proportion of INL to ONL thickness as it relates to refractive error/axial elongation.
376 subjects signed informed consents approved by the Indiana University IRB. Retinal thickness data was collected by SD OCT using 30 degree radial scans along with corneal topography (Medmont), refraction (Grand Seiko) and axial length/anterior chamber depth (IOLmaster, Zeiss). After automated segmentation, thickness ratios were calculated by dividing the INL thickness by the ONL thickness at every location along the horizontal and vertical plane. Data were then collected at 1 degree intervals +/-14 degrees from the fovea. Statistics were performed using repeat measures ANOVA in SPSS (IBM.) Subjects were categorized into emmetropes/hyperopes and myopes based upon a -0.75 diopter cutoff.
Myopes exhibited significantly lower INL/ONL ratios at locations peripheral to the fovea, beginning at 5 deg temporally and 7 deg nasally (P = 0.008), compared to the emmetropes/hyperopes. Both the INL and ONL were significantly thinner for myopes compared to emmetropes. Linear regression showed a mild correlation between refractive error and INL/ONL ratio at 5 degrees (y=0.0097X+0.3314, R2 = 0.162) and 10 degrees (y=0.0074X+0.2757, R2 = 0.121) temporal.
While both the INL and ONL were thinner in myopes, the INL/ONL ratio was reduced in the myopic group compared to the emmetropes/hyperopes. This suggests that outside the central fovea, the INL was comparatively thinner than the ONL in myopesfor myopes. In a radial stretch hypothesis, the ONL would be expected to be thinned to a similar extent compared with the INLdue to axial elongation, which was not supported by the data. The data also did not support a neural summation hypothesis whereby a larger number of photoreceptors connect to smaller number of cells, again expecting the ONL to be thinner relative to the INL.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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