Computerized stereochronoscopy and alternation flicker to detect optic nerve head contour change

Purpose/Background: Stereochronoscopy, a technique previously explored but abandoned for glaucoma diagnosis, viewed optic nerve images acquired at sep arate points in time as if a stereo pair. Prior efforts to exploit this tec hnique were impaired by a lack of superimposability for sequential optic ne rve images. We investigated computerized registration techniques for aligni ng sequential, monoscopic optic disc images to facilitate sensitive detecti on of optic nerve head contour changes in glaucoma. Design: Alogrithm and software development. Comparisons with standard techn iques. Materials: Existing patient records from the Glaucoma Service, Scheie Eye I nstitute, University of Pennsylvania. Methods: Two setsa of optic disc photographs, seperated in time by 1 to 18 years, of 25 eyes with and without glaucomatous optic disc progression were digitized. We developed custom software for accurate image alignment. Chan ge in disc morphology was then judged by digital stereochronoscopy and user -controlled alternation flicker of superimposed, time-separated images on a computer monitor. Comparisons were made with standard stereoscopic compari son. Main Outcome Measure: Identification of change or no change in optic nerve head contour for images acquired at separate points in time. Results: Image processing and registration permits accurate alignment of op tic disc photographs. Alternation flicker of superimposed, sequential image s facilitates image comparison and detection of change as indicated by chan ge in vessel position, color, and other cues for contour change. A high con cordance was found between standard stereoscopic comparison and alternation flicker. In several cases, reinspection of stereo comparison led to a revi sed judgment on the basis of disc changes rendered move obvious with altern ation flicker. Digital stereochronoscopy was less concordant with standard techniques. Conclusions: Digital image processing techniques and alternation flicker pr ovide a simple, sensitive, software-based method for detecting glaucomatous optic disc change. (C) 2000 by the American Academy of Ophthalmology.