If intraocular pressure plays a role in producing visual field loss in normal-tension glaucoma, there may be a possible benefit from therapeutic efforts to lower the pressure. To see whether pressure plays a role in the production of damage, we studied 14 cases of normal-tension glaucoma with asymmetric intraocular pressure (1- to 6-mm Hg interocular difference in pressure). In 12 of these 14 cases, we found that glaucomatous cupping and field loss (damage) was greater in the eye with higher pressure. This statistically significant correspondence of the higher pressure with the greater visual damage suggests that the level of pressure is a factor in producing optic nerve damage. Other factors also must contribute to account for the few instances in which damage asymmetry did not reflect interocular pressure-difference and for the occurrence of injury at such low levels of pressure in the first place. Although benefit may be expected from therapeutic lowering of pressure in this condition, the degree of benefit, as well as the side effects from treatment required for successful lowering of pressure, remains to be documented by a future clinical trial.