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Joel A. Papay, Christopher A. Clark, Toco Y. Chui, Liang Zhao, Ann E. Elsner; Distribution of Outer Nuclear Layer Thickness in SDOCT Images. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5664.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the thickness of the outer nuclear layer (ONL) as a function of eccentricity for younger vs. older subjects, comparing cone-rich areas to those with a higher proportion of rods. To examine individual differences in ONL thickness, minimizing the influence of disease and of eye size by limiting refractive error.
We analyzed the data from 31 subjects with normal retinal exams and refractive error < + 3 D, which reduced the effects of photoreceptor density differences due to potential disease or eye elongation. Subjects were divided into younger and older age groups, with an average age of 25.3 yr and 5 males and 13 females and 57.2 yr with 3 males and 10 females. We manually segmented SDOCT images, selecting 1 averaged B-scan of 1024 A-scans per subject, 20 deg horizontally through the fovea (Heidelberg Spectralis). We defined the region between the outer plexiform layer (OPL) to ONL boundary and the external limiting membrane (ELM) boundary, and using 3.87 microns per pixel computed the ONL thickness. Samples of smoothed ONL thicknesses were analyzed + 8 to 4 deg eccentricity, at .5 deg intervals, which minimizes the effect of the Henle fiber layer thickness on the measurements of the ONL thickness. We performed repeated measures ANOVAs, with the factors of age group and eccentricity, and a t-test on the refractive errors of each group.
The average ONL thickness decreased with eccentricity for both younger and older subjects (p < 0.001). ONL thickness computed from the average of nasal and temporal data decreased from 4 deg to 8 deg as follows: 72.6 to 57.4 microns for the younger subjects and 72.1 to 55.9 microns for the older subjects, respectively. There was no difference in refractive error, with a mean spherical error of -.67 and -.56 D for younger vs. older subjects, respectively (p < 0.83). There was considerable overlap between the age groups of the ONL thicknesses at all eccentricities.
ONL thinning in the macula occurred with increasing eccentricity, where the numbers of cone cell bodies are decreasing but rod cell bodies are increasing. The thinning of the ONL for both younger and older subjects occurred despite their low refractive errors.
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