A computerized digital image analysis system was developed to evaluate the retinal nerve fiber layer (RNFL) by red-free fundus photography. The image intensity of the RNFL was computed for 30 degrees between the disc and macula. Thirty early open-angle glaucoma patients and 30 normal age-matched subjects were examined. The coefficients of variation in the reproducibility of the measurements in normal subjects were 7.3 to 9.9% for the interphotographic studies, and 4.1 to 5.1% for the intraphotographic studies. Using this new image analysis system, the RNFL changes were detected easily and the glaucomatous eyes were distinguished from normal eyes with high sensitivity and specificity, 95% and 80%, respectively. This method will be useful for diagnosis of glaucoma at a very early stage.