Factors that influence the prevalence of positive catch trials in glaucoma patients

We evaluated factors that influence the catch-trial response in automated perimetry by consecutively examining 408 glaucoma patients (703 eyes) with either the program 30-2 or a 76-point screen with a quantified defect on the Humphrey Field Analyzer. The prevalence of positive catch trials using both programs was: 15.9% fixation losses, 5.5% false-positives, and 17.0% false-negatives. The only significant difference between the two programs was a lower prevalence of false-negatives on the program 30-2 (P less than 0.01). False-positive responses showed a significant positive correlation to fixation losses, and the catch trial response in general was correlated significantly to defect depth, test time, age, and visual acuity (P less than 0.05). This study suggests that the prevalence of positive catch trials is not an independent variable when testing glaucoma patients with automated perimetry and is not reduced by using a screening strategy over a full-threshold exam.