Time changes of contrast thresholds during automatic perimetry.

Contrast thresholds were continuously recorded in six points of the visual field through a repetitive up-and-down staircase method using the automatic perimeter developed by Heijl & Krakau (1975b). The uninterrupted sessions lasted about 30 min. Nineteen patients with a verified diagnosis of glaucoma, or in whom glaucoma was suspected, and twelve healthy normal subjects were tested. With increasing test time, a decreased contrast sensitivity was found. In most subjects the mean threshold increment was small (less than 1.5 dB). The threshold increments were larger in the patient group than in the normal subjects--many test points showing increments of 6-10 dB during the test session. Such a large deterioration of sensitivity was most common in eyes with visual field defects. Test points which showed large threshold increments were often situated in the vicinity of documented visual field defects. In eyes with pathological visual fields, the short-term variation increased with increasing test time. An impairment of fixation with increasing test time was found in the patient group.