Purchase this article with an account.
Dean VanNasdale, Ann Elsner, Christopher Clark, Stephen Burns; Phase Retardation Asymmetry Associated with the Henle Fiber Layer in Normal Aging. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1468.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To investigate and quantify phase retardation symmetry associated with the photoreceptor axons in the Henle fiber layer using non-mydriatic scanning laser polarimetry (SLP) imaging and custom image processing.
A scanning laser polarimeter (GDx, LDT/CZM) was used to acquire 15 deg macular images (256 x 256 pixels) in 40 clinically normal subjects evenly divided into 2 age categories, 20-29 and 70-79 years old. Two types of custom software were used for data analysis (Matlab, Mathworks). First, raw image data were used to compute macular cross phase retardation maps associated with the Henle fiber layer. Second, circular regions of interest were used to generate phase retardation profiles at 1.25 degrees eccentricity from the central macula. Phase retardation profiles were fit with a 2f sine function as a function of radial position around the fovea. Deviations from the function representing the superior half of the circular regions of interest were compared to deviations in the inferior half. The main effect of location, main effect of age category, and the interaction of the two were compared using repeated measures ANOVA.
The main effect of location and the interaction of location and age category were significant (p < 0.001 for both). Mean deviations were -0.034 and -1.22 grayscale units in the superior half of the phase retardation profile for the older and younger age category, respectively and 0.037 and 1.23 for the inferior half. The main effect of age category alone was not significant (p = 1.00) for the deviations from the circular fits, indicating that the fits to the older eyes were not worse than younger eyes, but rather quantitatively different.
SLP imaging demonstrates asymmetry in phase retardation associated with the Henle fiber layer measured close to the central macula, which is more pronounced in a younger population. Previous curve fitting analysis in a larger population provided clear-cut trends in phase retardation magnitude with age. The present asymmetry analysis provides a method to better quantify those changes, giving insight into the photoreceptor density across the central macula, which is difficult to visualize in many subjects using high-resolution techniques. This asymmetry could also influence methods to compensate for phase retardation originating from the anterior segment.
This PDF is available to Subscribers Only