Cupping of the optic disc in ischemic optic neuropathy.

Stereophotographs of the optic disc were reviewed in 78 patients with ischemic optic neuropathy (ION). Only 10% (6) of 61 nonarteritic (idiopathic) ION eyes developed optic disc cupping similar to that seen in glaucomatous eyes. Five of ten eyes with ION due to giant cell arteritis had cupping simulating glaucoma; however, two had elevated intraocular pressure, and the other three had large physiologic cups in the opposite eye. Optic disc pallor was proportionately more severe in ION eyes than in glaucomatous eyes of similar cup size. While there are similarities in the type of visual field loss in ION and glaucoma, the two disorders differ in the usual appearance of the disc after field loss has occurred and in the portion of the field most frequently affected. These observations suggest that if both disorders have an ischemic mechanism, there is a difference in the nature or distribution of the ischemia. There should be little difficulty under most circumstances in making the clinical differentiation between a disc that has suffered ION and a disc that has suffered pressure-induced damage, although occasional instances of ION may be classified as low-tension glaucoma on the basis of field loss and cupping without elevated intraocular pressure.