[Healthy optic discs with large cups--a diagnostic challenge in glaucoma]

Abstract

Background: Healthy optic discs with large cups are often characterised to be glaucomatous in automated, morphometric analysis. The aim of this study was to investigate the variables of laser scanning tomography (LST) and nerve fibre polarimetry of these disks in comparison to small and normal sized disks.

Methods: 117 eyes (age 49.3 +/- 14.6 years) with healthy, non-atrophic disks (md = 0.8 dB, Tensio 14.3 +/- 2.5 mmHg) of the Erlangen Glaucoma Registry were clinically examined. Morphometry was performed both by planimetry and the HRT I (Heidelberg Engineering, Dossenheim, version 2.01) and with the GDx FCC (Laser Diagnostics, San Diego). 63 eyes initially referred for a large cup were compared to 54 normal eyes. All measurements were analysed globally and in four sectors according to Jonas.

Results: The disc area of discs with large cups was significantly larger than that for the normals (3.1 +/- 5.3 vs. 2.2 +/- 4.2 mm (2)). Both the multivariate analysis of the HRT and the GDx revealed a significant correlation with total disk area (R = 0.34, p = 0.0001), with a high percentage of false positive glaucoma eyes among large disks. Cup area and volume showed, in contrast to rim volume and rim area, a significant correlation (R = 0.76, p = 0.0001) with the disc size. Thickness of retinal nerve fibre layer measurements both in HRT and GDx showed higher values for larger disc size with steeper cup measurements. The vertical diameter of the cup increased in comparison to the horizontal to a higher extent with increasing disc size.

Conclusions: By the pronounced enlargement of cup measurements, decreasing nerve fibre thickness values and decreasing ratio of temporal-to-inferior width of the neuroretinal rim, large disks may easily be detected as false glaucomatous by morphometric analysis systems. A better presentation of large discs in a normative database and integration of sectors and disc area in a multivariate analysis may improve the diagnostic abilities of automated morphometric disk analysis.