The normalised rim/disc area ratio line

Abstract

The assessment of the cup of the optic disc depends, among other criteria, on the disc area. A small cup in a small optic disc can indicate an advanced glaucomatous lesion, on the other hand a large cup in a large optic disc can be normal. Therefore, an individual normalised rim/disc area ratio line together with the curves of 50th percentile and the 95th percentile of normal could help to better distinguish between glaucomatous and normal optic cups. The aim of our study was to calculate and to evaluate such a normalised rim/disc area ratio line. Heidelberg Retina Tomograph examinations of the optic nerve head of 100 randomly selected eyes of 100 normal subjects were evaluated. We calculated the disc area adjusted rim/disc area ratio in sectors of 10 degree. The 95th percentile and the 50th percentile of each of the 36 sectors were calculated. Based on these normal percentile lines it was possible to display an individual normalised rim/disc area ratio line in the topographic images of an individual optic disc examination. Here we demonstrated examples of a normal optic disc, optic nerve heads with moderate and advanced lesions and a small optic disc with glaucomatous damage. We present a new display mode of the results of Heidelberg Retina Tomograph optic nerve head examination, which may be helpful for an easy and reliable assessment of glaucomatous optic nerve head damage only looking at topographic images.