Principles of photometry of the papilla.

To enhance the qualitative information gained by photographing the optic nerve head, we built a silicon photovoltaic detector (photodiode) in the image plane of a fundus camera (Zeiss). It permitted quantitative evaluation of the relative brightness of the illuminated papilla. Following construction of the device and during the early course of more than 260 measurement sessions (on more than 130 subjects), several heretofore unknown sources of error were encountered and subsequently dealt with, resulting in a margin of error for the entire system of between 0.3% and 1.2%. Pallor of the optic nerve head induced by artificial ocular hypertension can be well reproduced by this method.