Focal and diffuse visual field defects: their relationship to intraocular pressure

The view that visual field loss in "low-tension" glaucoma (LTG) is more focal than in ordinary or "high-tension" glaucoma (HTG) is controversial. The basis of the controversy may be the inappropriate presupposition that an arbitrary intraocular pressure (IOP) level effectively differentiates these entities. We attempted to determine whether meaningful differences exist between glaucoma patients classified on the basis of pattern of visual field loss rather than IOP. One hundred consecutive glaucomatous visual fields were classified as focal or diffuse by two independent observers masked to all other clinical information. Several clinical parameters were then evaluated, comparing patients with focal visual field loss, with those with diffuse loss. Maximal pretreatment IOP was significantly lower among the patients with focal visual field loss than it was among those with diffuse loss (21.5 mm Hg +/- 5.7 vs 25.9 mm Hg +/- 4.7; P < .01). There was no difference between the two groups in terms of age, blood pressure, visual acuity, or color vision. We conclude that focal glaucomatous visual field loss occurs at a lower IOP than diffuse loss and, as such, may be a marker by which to identify patients whose optic nerves are abnormally susceptible to glaucomatous injury.