Factors associated with intraocular pressure-induced acute visual field depression

Abstract

Objective: To determine the factors associated with visual field depression produced by artificial elevation of intraocular pressure (IOP).

Methods: The visual threshold was determined at 26 locations in the central visual field at a spontaneous IOP, at 30 mm Hg, at 40 mm Hg, and at the IOP immediately following release of the suction cup used to elevate the IOP artificially in 33 subjects with and without glaucoma. The net decrease in threshold sensitivity at each IOP level relative to sensitivity obtained at the spontaneous IOP was calculated (acute visual field depression).

Results: Factors potentially influencing the acute visual field depression between subjects were determined with stepwise regression. The reciprocal of ocular perfusion pressure, a clinical measure, was strongly correlated with acute visual field depression (dependent variable), particularly at 40 mm Hg (at 30 mm Hg, r=0.412, P=.02, n=32; and at 40 mm Hg, r=0.813, P<.001, n=33). When a second variable, the diagnosis of glaucoma, was included in the regression at 40 mm Hg, it contributed significantly (partial r=0.650, P<.001, n=26). The degree of glaucomatous damage (vertical cup-disc ratio or baseline Humphrey 24-2 visual field mean deviation) failed to correlate with acute field depression, with or without correction for ocular perfusion pressure.

Conclusions: The elevation of IOP produces acute, reversible visual field depression. This depression is largely dependent on the subject's ocular perfusion pressure. The degree of depression is greater in those with glaucoma but is not strictly related to the degree of glaucomatous damage.