Retinal Birefringence in Normal Eyes and in Exudative Eye Disease

Abstract

Purpose:: To detect exudation using birefringence and other retinal polarization properties. To determine whether the fine scale changes in retinal birefringence in exudative eye disease can be distinguished from normal variations across the macula or stress due to retinal elevation. To extend the model of radially symmetric foveal birefringence to a larger region of the posterior pole.

Methods:: A scanning laser polarimeter imaged 15 x 15 deg of retina at 780 nm with 20 input polarizations. Light from the eye was digitized at two detectors, one parallel to the input polarization and the other crossed, producing 40 images at 256 x 256 pixel resolution and 8 bits of grayscale. Images that varied in polarization content were computed, including a birefringence amplitude image (the modulation of crossed detector signal), and the phase of the maximum modulation displayed in pseudo-color with a Cardinal Directions Scale. Retinal birefringence was compared for 18 control subjects (19-80 yr) and patients with exudative retinal disease: 36 with age-related macular degeneration (AMD), 14 with diabetic retinopathy, and 15 with central serous retinopathy. Birefringence amplitude and phase were separately examined for a) fringes around fluid indicating altered retinal geometry, b) striae indicating traction, and c) other focal changes possibly associated with molecular changes. Superior field images provided comparison for macula and optic nerve head bundle in control subjects.

Results:: Focal changes in the phase of the birefringence were common in patients: e.g. 94% of the exudative AMD patients beyond the striae and fringes findings. Control subjects of all ages had macular crosses visible in both the amplitude and phase images, and no focal changes in the phase of birefringence. Focal amplitude changes in birefringence were more typical in older subjects (p = 0.118). The phase of the maximum birefringence rarely matched for fiber bundles and Henle fibers oriented similarly in the xy plane, with large individual differences in the position of retinal vessels and the amplitude of nerve fiber bundle birefringence relative to the macular cross.

Conclusions:: Retinal birefringence maps in the normal eye have few qualitative features beyond the macular cross and nerve fiber bundles, although differ quantitatively. As eyes with exudation have many focal changes in birefringence, this mode of imaging may complement confocal or depolarized light imaging to improve disease detection.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • age-related macular degeneration • imaging/image analysis: clinical