Computerized measurement of the three-dimensional distribution of optic disc pallor

Purpose. To describe a method which provides quantitative measurements of the surface area of pallor in each quadrant of the three-dimensional optic cup, using photogrammetric measurements from simultaneous stereophotographs and computerized image analysis. Methods. Simultaneous stereophotographs of one normal subject and two subjects with primary open angle glaucoma were digitized and analyzed for depth measurements. The boundaries of the optic disc, optic cup and region of pallor were identified. Pallor/disc and pallor/cup ratios were subsequently calculated for the superior, temporal, inferior and nasal walls. Results. A digitized photograph and a Laplacian-filtered image were obtained for each eye to be studied. After processing each stereo pair through a similarity sequential detection-based algorithm, depth measurements are represented as a grey scale image, a contour plot, and a wire mesh, with the boundaries of the optic disc, optic cup and pallor superimposed. Ratios are given of the surface area of pallor to the surface area of the disc and the surface area of pallor to the surface area of the cup, by quadrant. Conclusions. Determination of surface area of pallor to cup may be useful in detecting early visual field loss in glaucoma and neurological disease.