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Tianjiao Zhang, Christine A Curcio, Yuhua Zhang; Variability in human cone topography enabled by adaptive optics scanning laser ophthalmoscopy (AOSLO) imaging of foveal centers. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5885.
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© ARVO (1962-2015); The Authors (2016-present)
Accurate assessment of variability of the human cone topography is important for interpreting the effects of aging and disease on the photoreceptor mosaic. We measure foveal cone densities to acquire a better estimation of variability between eyes of single individuals and between individuals, using a new generation research AOSLO.
Forty eyes of 20 subjects with normal retinal health aged 19-29 years were studied. The refractive errors of the participants range from -3.0 D to 0.63 D and the fellow eye refractive error difference of individual subject is less than 0.50 D. AOSLO was performed to image the cone photoreceptors. Cone density was assessed on a two-dimensional mesh grid over the central 2.4 mm x 2.4 mm macula at up to 139 points. Mean cone densities, standard deviation, the coefficient of variation (CV), and cumulative cone numbers as a function of eccentricity were calculated to estimate the inter-subject variability. Cone density difference between fellow eyes was statistically assessed with a mixed model approach and quantified by the root-mean-square (RMS) and the maximum difference.
The peak densities of all eyes are 168,162 ± 23,529 cones/mm2 (mean ± SD) (CV = 0.14). The mean cone density agrees well with the histological data (p = 0.9983 for both eyes). The total number of cones within the cone-dominated foveola is 38,311 ± 2,319 (mean ± SD) (CV = 0.06). The RMS cone density difference between fellow eyes is 6.78%, and the maximum intra-subject difference is 23.6%. There is no difference in the association between eccentricity and cone density in fellow eyes for the superior/nasal (p=0.8503), superior/temporal (p=0.1551), inferior/nasal (p=0.8609), and inferior/temporal (p=0.6662) quadrants of the retina.
By measuring the foveal center cone density in a large number of eyes, we were able to determine the center of many retinae, thereby accurately assessing the cone density variability. Our results agree well with data provided by classical histology. We have confirmed that in living human eyes, though cone densities vary significantly in the fovea, the total number of cones within the cone-dominated foveola is less variant both within and between subjects. Thus, the total number of foveola cones may serve as an important measure for assessing cone loss due to aging or disease.
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