Improved Contrast of Peripapillary Hyperpigmentation Using Polarization Analysis

Abstract

To improve detection and quantification of peripapillary hyperpigmentation, associated with aging, open-angle glaucoma, and age-related macular degeneration. A computational approach was implemented with a readily available polarimeter used in glaucoma diagnosis, a nerve fiber analyzer (GDx; Laser Diagnostic Technologies, San Diego, CA). Using near-infrared illumination at each of 20 input polarizations, a series of image pairs was digitized. One image is made from the light returning from the eye that is polarized parallel to the input light, and the other image is made from the light that is rotated by 90 degrees from the input polarization. Using raw data from these 40 images, and a simplified model of ocular polarization properties, images were computed based on their polarization content. Regions of hyperpigmentation, selected using stereo color fundus photographs, were quantified in three types of polarimetry images: (1) a depolarized light image resulting mainly from multiply scattered light; (2) an average image that is typical of confocal images; and (3) a birefringence image. Measurements on versus off hyperpigmentation were made in nine persons with suspected glaucoma or patients with primary open-angle glaucoma, selected to have clinically visible hyperpigmentation. In the depolarized light images, hyperpigmented regions were significantly brighter than comparison areas (P < 0.0425)-that is, had more scattered light and therefore more contrast (P < 0.037) than did color or other polarimetric images. With this polarimetry imaging method, subretinal tissues such as those with hyperpigmentation can be visualized with increased contrast.