Abstract

PURPOSE:

This study assessed agreement in optic nerve head parameters between 2 investigators independently contouring Heidelberg retina tomograph II (HRT II) optic disc images of normal elderly subjects.

PATIENTS AND METHODS:

Contours were drawn by both investigators on 550 randomly selected optic discs of 550 normal elderly patients (mean age, 73.1 y) drawn from a population-based study. All subjects had normal intraocular pressures and visual fields. Coefficients of variation were calculated for interobserver and intraobserver variability.

RESULTS:

The mean disc area was 1.97 mm, with no relationship between magnitude of disagreement and the mean. There was a significant bias between investigators with a mean difference in disc area of -0.06 mm. The 95% limits of agreement of disc area were -0.59 to +0.47 mm. Ninety-five percent coefficients of agreement (1.96 SD of the parameter differences between investigators/mean parameter value x100) were similar for global and sectoral disc areas (26.7% to 32.3%). Respective coefficients for rim area, cup area, and rim volume were much higher at 35.2%, 48.5%, and 76.5% respectively, but much lower for rim/disc area ratio (12.7%). There was no significant correlation between disagreement and grade of cataract or HRT image quality.

CONCLUSIONS:

Disagreement in contour placement can be substantial, with disproportionate effects on some calculated HRT parameters. Image quality and lens opacity have no significant influence on the degree of disagreement. Rim/disc area ratio is the HRT parameter least affected and may be more useful in comparing normative databases and diagnostic studies between centers.