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Christopher Clark, Ann Elsner, Benjamin Konynenbelt, Joel Papay, Toco Chui; Outer nuclear layer and retinal layer ratios in myopic and emmetropic populations using spectral domain optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1907.
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© ARVO (1962-2015); The Authors (2016-present)
Cone photoreceptors have been shown to vary considerably between individuals both centrally and peripherally. When incorporating retinal growth signals such as defocus, this variability may influence refractive development. The purpose of this study is to examine differences in photoreceptor density across the retina in myopic and emmetropic populations.
80 subjects right eyes were imaged for this study (age range: 22 to 34, refractive error: -10 to +5.00.) Thirty degrees OCT (Spectralis, Heidleberg) images were collected in a radial pattern along with peripheral refraction (Grand Seiko) and peripheral axial length measurements (IOLmaster, Zeiss.) OCT images were segmented with custom software to determine the thickness of the total retina, ONL, OPL, and INL. Lateral magnification and tilt effects were corrected. In addition to thickness measurements, a ratio was calculated for the layers by dividing peripheral thickness by each subjects central thickness, thereby reducing individual variation. Statistics were performed using repeat measures ANOVA in SPSS (IBM.)
Total retinal thickness (TRT) and ONL was relatively thinner for myopic subjects compared to emmetropic and hyperopic subjects (P = 0.007.) This effect was larger in the periphery with no effect centrally. ONL differences between refractive groups were relatively small (average difference of 21 microns.) Likewise, longer axial lengths resulted in thinner TRT and ONL in the periphery but no effect centrally (P = 0.02.) There was a negative correlation between a subject’s TRT or ONL and the ratio of peripheral to central TRT or ONL (P < 0.00,) except for the longest eyes (P = 0.56). Central and peripheral thicknesses were uncorrelated.
Retinal and ONL thickness decrease with axial length and refractive error. The primary hypothesis for this is due to stretch factors during elongation though a longitudinal study is needed to confirm this. An alternative hypothesis would be that the signal strength from denser vs. sparses photoreceptors and retinal neurons could influence axial length and refractive development. Further, ONL and TRT are controlled by at least 2 factors, total numbers and foveal specialization.
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