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Dean A. VanNasdale, Ann E. Elsner, Todd D. Peabody, Kimberly D. Kohne, Victor E. Malinovsky, Bryan P. Haggerty, Anke Weber, Stephen A. Burns, Christopher A. Clark; Polarization Sensitive Alterations to Photoreceptor Axons in Age-related Macular Degeneration. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3080.
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To use non-mydriatic scanning laser polarimetry (SLP) imaging, custom image processing, and a quantitative model, to emphasize birefringence associated with the photoreceptor axons in the Henle fiber layer. To quantify and compare the regularity of photoreceptors in the central macula in patients with non-exudative age-related macular degeneration (AMD) and age-matched controls.
A scanning laser polarimeter (GDx, LDT/CZM) was used to acquire 15 deg macular images (256 x 256 pixels) in 25 patients with non-exudative AMD and 25 age-matched, clinically normal subjects. Raw image data were used to compute macular cross phase retardation maps associated with Henle fiber layer in the central macula. Consecutive, annular regions of interest ranging from 0.5 - 3 deg eccentricity, centered on the fovea, were used to generate intensity profiles from the phase retardation data, which were then analyzed using a fast Fourier transform (FFT). The outcome measure is based on the 2f and 4f FFT components, representing the majority of the radial symmetric birefringence found for normal Henle fiber layers, which are normalized by the remaining FFT components. The magnitude of the difference between the two groups was analyzed as a function of eccentricity, using a paired t-test. Also, the location at which the outcome measure was largest for each subjects was compared for the two groups, along with the value of the outcome measure at that location using paired t-tests.
The normalized 2f and 4f FFT components were lower in the AMD group than in the matched controls at each eccentricity between 0.5 and 3 deg (p<0.001). There was no difference in the eccentricity that yielded the maximum normalized 2f and 4f FFT components, 1.91 deg in the AMD group and 1.91 deg in the control group (p=0.911), or the value of the normalized 2f and 4f FFT component at that discrete location (p = 0.135).
These radially symmetric birefringence changes in the central macula indicate loss and/or structural alterations to the cone photoreceptor related to non-exudative AMD. Previously reported foveal birefringence changes associated with normal aging could mask these AMD changes. Birefringence measurements over the entire macula, instead of discrete locations, provides better discrimination between AMD patients and controls.
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