Stereochronometry: quantitative measurement of optic disc cup changes

Abstract

The authors have developed an objective, quantitative method for detecting optic disc cup changes that occur with time. Called stereochronometry, this new technique uses a stereoplotter to measure changes recorded in the combination of two single photographs taken of the same optic disc at different times. The reproducibility and sensitivity of stereochronometry were evaluated using a model eye. Stereochronometric measurements were significantly correlated with calibrated changes of depth and width of the cup of the model eye. Standard deviations for five measurements of cup changes without camera shift range from 2 microns to 18 microns, and errors (deviations of the mean of measurements from calibrated cup changes) ranged from -26 microns to +33 microns. Standard deviations and errors in the measurement of cup depth and width were significantly increased when the camera was shifted by 2.5 mm between photographs to simulate possible changes in photographic conditions.