Comparison of the optic nerve head in high- and low-tension glaucoma.

The optic nerves of 34 eyes of 34 patients with low-tension glaucoma were compared with those of 41 eyes of 41 patients with high-tension glaucoma. Mean intraocular pressure in the low-tension group was 16.9 +/- 0.7 mm Hg (mean +/- SEM) compared with 31.7 +/- 0.8 mm Hg in the high-tension group. Mean total visual field loss was not significantly different in the two groups, as determined by computerized threshold perimetry (OCTOPUS). The optic disc rim in low-tension eyes was significantly thinner than in high-tension eyes (P = .018); the largest difference occurred inferiorly and inferotemporally (P less than .001). The appearance of the optic nerve is useful to distinguish between these two subtypes of glaucoma and may be a more meaningful indicator than intraocular pressure. Our findings support the hypothesis that there are at least two different mechanisms for optic nerve damage in glaucoma.