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Karl G. Csaky, Kelly Locke, David G. Birch, Muneeswar Nittala, SriniVas Sadda; Structure - Function Correlates in the Retina Surrounding Geographic Atrophy (GA): A Comparison Study of Peri-GA Scotopic Sensitivities and Retinal Anatomic Parameters. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5261. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
GA is a relentless disease that progresses at various rates from the central retina outward. While information has been gathered on the anatomic parameters of the immediate GA edge, little is known about the retina outside the central GA.
5 eyes from patients with at least 1-disc area of central GA (range 1.2 - 9.3 DA) and soft drusen were examined. Following appropriate dark adaptation, rod -mediated sensitivities were measured from retinal areas within the retinal arcades but outside the area of central GA using a modified fundus microperimeter (MP-1S, Nidek Technologies). Subsequently SD-OCT scans (Spectralis HRA+OCT) were obtained from the retina. Thickness measurements of the neurosensory retina, outer nuclear layer (ONL), inner segments (IS), outer segments (OS), and retinal pigment epithelium (RPE) in the areas corresponding to the retinal sensitivities were quantified using 3D-OCTOR software for retinal layer segmentation. 3D-OCTOR allows importation of raw OCT image data and manual segmentation of retinal boundaries. Dimensions of the B-scan image were used to convert the number of pixels between the inner and outer retinal boundaries into a thickness measurement at each A-scan location.
The overall mean scotopic retinal sensitivities = 17 dB ± 10 (mean ± SD) while the thicknesses for the retinal structures were (mean ± SD, min-max), neurosensory retina (263 um ± 49, 190-368 um), ONL (59 um ± 23, 0 - 124 um), IS (20 um ± 9, 0 - 39 um), OS (25 um ± 9, 0 - 43 um), and RPE (19 um ± 7, 0 - 31 um). Correlation analysis (Pearson coefficient) demonstrated that of the various retinal anatomic parameters, only RPE thickness correlated with scotopic retinal sensitivities (r=0.379, p<0.001). In multivariate correlations, only the total retinal thickness and RPE thickness correlated significantly with retinal sensitivities (cumulative R square = 0.26).
In this preliminary study, loss of rod sensitivities in the peri-GA region appears to occur without correlation to anatomic changes in the neural retina as detected by SD-OCT and appears to represent an example of function-structure mismatch. An on-going clinical trial will continue to shed light on the concept that loss of the RPE may be associated with rod photoreceptor dysfunction and that therapies for the peri-foveal GA region should be directed at improving the status of the RPE.
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