False-negative responses in glaucoma perimetry: indicators of patient performance or test reliability?

PURPOSE To study whether false-negative answers in computerized glaucoma perimetry indicate the patient's ability to perform perimetry or test result reliability. METHODS A retrospective evaluation was performed of visual field test results obtained with a perimetry program (Humphrey 30-2 Sita Standard; Humphrey Instruments, San Leandro, CA) in 70 consecutive patients with unilateral glaucomatous field loss. Frequencies of false-negative answers were compared between the two eyes of each patient and related to amount of visual field damage in the glaucomatous eyes using linear regression analysis. RESULTS Frequencies of false-negative answers were higher in eyes with field loss. The intrapatient intereye difference was 6.6% on average (P < 0.0001). In seven subjects with false-negative frequency of 5% or more in both eyes, the mean difference was 12.7% between eyes. The differences in false-negative answers depended significantly on the amount of field loss in the glaucomatous eyes (P = 0.0003). Larger differences were seen in patients with advanced field loss in the affected eye. CONCLUSIONS The increased frequencies of false-negative answers in eyes with field loss were strongly associated with field status. The higher false-negative frequencies in eyes with glaucomatous field loss compared with unaffected eyes may be explained by the increased variability in threshold values typically found in such eyes. False-negative answers in patients with glaucoma therefore represent eye rather than patient status.