Interocular asymmetry of optic disc size and its relevance to visual field loss in normal-tension glaucoma

We evaluated the relevance of interocular asymmetry of optic disc size to the level of intraocular pressure and the extent of optic disc and visual field changes in normal-tension glaucoma (NTG). Fifty-two eyes of 26 patients with NTG were measured for optic disc topography using a computerized image analysis system (IMAGEnet, Topcon), diurnal intraocular pressure (IOP), and Octopus automated visual field. Of the 26 patients, 22 had interocular asymmetry of the optic disc area of at least 0.01 mm2 and of mean IOP of at least 0.3 mmHg. Of these 22 patients, 8 had the higher mean IOP in the eye with the larger optic disc. In these 8 patients, the visual field defect was significantly more advanced in the eye with the larger optic disc (Wilcoxon signed ranks test, P < 0.05). These findings appear to support the hypothesis that an eye with a large optic disc may be more vulnerable to a rise in IOP.