The reproducibility of computerized boundary analysis for measuring optic disc pallor in the normal optic disc

The optic discs of eight normal subjects were photographed on three separate visits under widely varying conditions. Each photograph was scanned by a television camera, converted to digital form, and then analyzed using computer image analysis techniques. The computer was programmed to delineate the boundary around the optic disc and the area of pallor. The percentage of disc pallor was then computed across the entire disc and for each disc quadrant. The reproducibility of the procedure was determined by evaluating several photographic parameters: camera flash intensity, film type, magnification, and centering of the disc in the photograph. The focus adjustment on the television scanner was also varied. Under carefully controlled conditions, results showed that the reproducibility of measuring the total percent of disc pallor was 2%. Results for reproducibility are also given for less than optimal conditions and for manual planimetry on the same set of photographs.