DEPTH MAPS FROM STEREO IMAGES OF THE OPTIC DISC

Glaucoma is a chronic disease whose causes are not well understood. It is estimated that three million Americans have glaucoma, and 67 million people worldwide will have glaucoma by the year 2000. At least half do not know they have it because glaucoma usually has no symptoms in the early stages. Untreated, glaucoma is a leading cause of irreversible blindness. An important goal of current research is to develop methods of early diagnosis to detect the disease in the early stages, when treatment is most effective in minimizing irreversible vision loss. Currently, the identification of early pathologic changes at the optic nerve head (ONH) is crucial to the diagnosis of glaucoma. The current gold standard for measuring these changes is through clinical stereoscopic observation of the ONH. From the American Academy of Ophthology (AAO) 2000, "Previous studies have found that the diagnostic precision of qualitative evaluation of stereoscopic ONH photographs by experienced clinical observers is superior to any other currently available method of optic disc assessment." (Identifying Early Glaucomatous Changes, Wollstein, Health, 2000 AAO). The major drawback to the stereoscopic evaluation is the subjectivity which creating inter and intra-observer reader variability. A new method for evaluation to stereoscopic photographs is needed for consistent analysis of the changes on the optic nerve head. This can be brought about by the use quantitative analysis of the ONH changes. The phase I project will be used to improve a technique for calculating disparity maps based on a pair of stereoscopic images. This technique has already proven to give good results, though it needs to be tuned for this specific application. Once the topography is found, basic image processing algorithms can be used to locate the disc and cup boundaries and calculate the volume of the cup. The algorithm will be compared to several pre-diagnosed cases for testing the accuracy. This will lead to the Phase II project, which will use digitized stereoscopic image of the optic nerve head for longitudinal measurements. These measurements will include three-dimensional changes in the dimensions of the cup and disk over a period of time. The measurements will be calculated on pre-diagnosed images for comparison with and expert reader. Collaborators from the University of Iowa and the University of Texas Medical Center in San Antonio will provide these analyses.