Optimizing and validating an approach for identifying glaucomatous change in optic nerve topography.

PURPOSE To determine and validate optimal parameters for analysis in a previously described approach for identifying glaucomatous optic nerve progression by scanning laser tomography. METHODS Thirty-degree sectors of rim area, as defined by an experimental reference plane, were analyzed for change with respect to different statistical limits of variability (80%, 90%, 95%, 98%, 99%, and 99.9%) in the longitudinal image series of 62 eyes from 30 ocular hypertension converters and 32 normal control subjects. A criterion requiring that change is repeatable in two of three consecutive tests (the 2-of-3 criterion) was compared with a single-test strategy not requiring confirmation, and four other plausible criteria. The influence of these various parameters on sensitivity and the false-positive rate was evaluated. The same series were also assessed for change by the known method of computer-generated probability maps. RESULTS More sectors were identified as progressing in converter eyes than in control eyes at every limit of variability. With stricter limits of variability and a requirement of confirmation, fewer sectors were identified as changing, especially in control eyes. The 2-of-3 criterion had the most favorably balanced sensitivity and false-positive rates: these were, for the 90% limit of variability, 90.0% and 6.2%, respectively, and for the 95% limit, 83.3% and 3.1%, respectively. Confirmed rim loss in converter eyes was most frequent in the disc poles and corresponded with the field hemisphere of conversion in 80%. Probability maps detected significant and repeatable change in 26 (86.7%) of 30 converter eyes and 14 (43.8%) of 32 of control eyes. CONCLUSIONS This study was conducted to optimize and validate an approach for identifying progression. The method distinguished eyes with glaucomatous change from unchanging control eyes.