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Q. Zhou, B. P. W. Lo, R. W. Knighton, S. W. Cousins; Fundus Depolarization Imaging With Scanning Laser Polarimeter in Normal Eyes and Eyes With Dry AMD. Invest. Ophthalmol. Vis. Sci. 2009;50(13):344.
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To test our hypothesis that fundus depolarization as measured with a scanning laser polarimeter (SLP) provides a surrogate measure of aging and pathological changes in the RPE and the RPE-Bruch’s membrane junction.
A commercial SLP system, GDx VCC, was modified with the internal fixation target centered in the scan field. A depolarization image (the ratio of depolarized light to the total light) was derived from the GDx image series and saved in the database with the reflectance image and the phase retardation image. Clinical data to test the feasibility was collected at Duke Eye Center. Twenty-three normal eyes (23 normal subjects, one eye per subject randomly selected), 18 dry AMD eyes (13 subjects) without detectable geographic atrophy (GA), and 10 dry AMD eyes (6 subjects) with GA were included in the study. The age distributions (Mean±SD) of the normal group, dry AMD w/o GA group, and the dry AMD with GA group were 51.7±15.1, 76.3±8.3, and 81.1±6.1 respectively. Two GDx VCC measurements were acquired per study eye. The mean depolarization and the standard deviation (STD) of depolarization were derived from a 10°x10° area centered on the fovea and averaged over 2 measurements per study eye.
In the normal eyes, depolarization was usually higher nearer the fovea; for the central 10° x10° region, the mean depolarization increased with age significantly at a rate of 0.003/yr. (r=0.79, p<.0001) and the uniformity of depolarization image (measured in STD) increased with age slightly at a rate of 0.0002/yr. (r=0.56, p=0.052). After correction of normal age-related increase, the dry AMD eyes w/o GA had significantly lower mean depolarization (p<.001) and significantly higher STD of depolarization (p=.011) than the normal eyes. GA appeared as clearly hypo-depolarizing regions, supporting the RPE-Bruch’s membrane junction as the origin of depolarization.
Quantitative macular depolarization maps may provide information about both spatial distribution and heterogeneity of age-related changes in the outer retina, especially within RPE and incipient subRPE deposits. We hypothesize that depolarization mapping will identify eyes with subclinical deposit formation and other Bruchs membrane changes of early AMD prior to the development of clinically evident drusen.
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