Measurement of optic disc parameters on digital fundus photographs: algorithm development and evaluation

To develop and evaluate a simple and rapid algorithm for optic disc measurements on digital fundus photographs, relying on the macula-disc centre distance as a reference when converting length expressed in pixels to metric distance. Measurements were performed on fundus photographs from 68 normal subjects, acquired using five different cameras. The magnification factor and actual size in mu m of 1 pixel was known for only one camera. The measurements from this camera were compared to corresponding measurements from a confocal scanning laser ophthalmoscope. Using the described algorithm, no significant differences in mean disc or cup size were observed between the tested cameras, despite differences in magnification factor (range 0.5-2.5). There were no significant differences between disc and cup measurements obtained with the confocal scanning laser ophthalmoscope and those obtained with the described algorithm in the 20 subjects examined. The algorithm described in the current study provided clinically relevant measurements of optic disc parameters. The final program can be used directly on the acquired images, with the examined subject still available for re-examination.