LIMITS OF 2-DIMENSIONAL PLANIMETRY IN THE FOLLOW-UP OF GLAUCOMATOUS OPTIC DISKS

Background: To test the intra-observer, intra-photographic variability of two-dimensional measurements of the optic nerve head we used compu ter-assisted planimetry. Depending on the variability, we calculated t he confidence intervals of the optic disc parameters which could be in dicative of glaucomatous damage on follow-up. Methods: Slides of the o ptic disc were taken from 10 eyes of 10 patients (n = 6 open angle gla ucoma, n = 4 ocular hypertension) using a Zeiss fundus camera. All eye s were evaluated 10 times within a random sequence on 10 different day s. We obtained the absolute values of the disc radii and the cup radii in steps of 1, 10, and 45 deg in predefined quadrants and the mean ra dii. Results: The confidence interval of the cup radius on follow-up, depending on sector size, ranged between 62 and 38 % for small cups (r adius 0.2 mm) and between 12 and 7 % for large cups (radius 0.8 mm). T he confidence intervals of the cup/disc ratio distinguishable from the disc boundary, depending on sector size, ranged between 0.81 and 0.89 for small discs (radius 0.5 mm) and from 0.90 to 0.94 for large discs (radius 1.0 mm). The confidence intervals of the cup/disc ratio indic ating an increase on the cup radius in follow-up, distinguishable from the boundary of the disc, ranged, depending on sector size, between 0 .57 and 0.75 for small discs (radius 0.5 mm) and from 0.81 to 0.89 for large discs (radius 1.0 mm). Conclusion: The smaller the disc, the mo re difficult is the detection of glaucomatous damage, and the larger t he cup, the more difficult is the detection of progression of glaucoma tous damage.