Glaucomatous optic nerve damage has generally been associated with high cup-to-disc ratios. Fifteen eyes of nine patients with increased intraocular pressure and glaucomatous visual field loss but low cup-to-disc ratios are reported. The optic disc area was significantly (P less than 0.01) smaller than in 429 normal subjects and 556 glaucoma patients with high cup-to-disc ratios. Parapapillary chorioretinal atrophy was significantly larger and retinal nerve fiber bundles were significantly less visible than in the normal group. The latter two parameters were not significantly different in the glaucoma groups with low and high cup-to-disc ratios when the groups were matched for mean perimetric loss. The authors conclude that in eyes with small optic discs, glaucomatous optic nerve damage may be indicated more sensitively by parapapillary changes than by cup-to-disc ratios. Glaucomatous eyes with small optic nerve heads can have misleadingly low cup-to-disc ratios.