Imaging Polarimetry in Macular Exudation and Atrophy

Abstract

Abstract: : Purpose: To detect and localize retinal pigment epithelium disease and exudation, rapidly and noninvasively, using a novel image analysis method for polarized light. To test whether pathology in the superficial retina can be imaged separated from that deeper in retinal or subretinal layers. The hypothesis is that light that retains polarization has reflected back off superficial retinal layers, while the light more randomly polarized has been scattered multiple times when passing in and out of the retina. Methods: The maculas of 38 patients were imaged. The 27 patients with advanced Age-Related Macular Degeneration (AMD) had either classic or occult choroidal neovascularization (CNV), pigment epithelial detachment, or geographic atrophy less than 2 disc diameters. A second group had 2 younger patients with CNV and 9 with central serous retinopathy (CSR). Scanning laser polarimetry (GDx, LDT) provided raw image data in 1 sec of 20 image pairs that varied in illumination polarization angle, and simultaneously sampled at crossed and uncrossed polarizations. The birefringence image was computed from the light that modulated with input polarization. A depolarized light image was computed from the portion of the light that was unmodulated for each pixel. Standard confocal images were also computed. Images were graded for visibility of striae, fluid, and pigmentary changes. Results: The depolarized light images most readily showed RPE pigmentary changes (P < .0001 for AMD) in many cases with overlying fluid. The area of fluid leakage was localized clearly in the standard confocal images, and most poorly in the birefringence image (P < .0001 for AMD, < .015 for CSR/young CNV). The birefringence image visualized fine striae around the areas of leakage (2/3 of patients with AMD (P < .00001). Conclusions: Polarization imaging provides a means to visualize and segregate information in RPE disease, in some image types visualizing pigmentary changes through fluid and in others clearly localizing the boundaries of the fluid.

Keywords: age-related macular degeneration • choroid: neovascularization • imaging/image analysis: clinical