Reproducibility of photogrammetric optic disc cup measurements

To detect early glaucoma-associated changes in the optic disc cup, the authors analyzed reproducibility of optic disc cup measurements by photogrammetry of three age-matched groups: 10 normal, 10 ocular hypertensive, and 10 glaucomatous subjects. For each eye, three simultaneous stereophotographs were taken on the same day and one measurement was made for each stereophotograph. In order to reduce the effects of refractive error of the eye and photographic magnification, the authors computed cup parameters as relative measurements, ie, a ratio to the optic disc area. The median coefficients of variation for glaucomatous eyes were 4.5% for cup volume/disc area, 6.1% for cup depth/disc area, and 4.7% for cup area/disc area. Coefficients of variation of normal and ocular hypertensive subjects were slightly larger than those of glaucomatous subjects. Coefficients of variation generally were larger for quadrants than for total disc area. These findings suggest that the photogrammetric technique is highly reproducible and sensitive and could be a valuable quantitative technique for the clinical study of glaucoma.