The influence of stimulus parameters on the visual field indices by automated projection perimetry.

The various stimulus parameters offered by two standard automated projection perimeters [Humphrey Field Analyser 630 (HFA) and Octopus 201], namely, stimulus size and location and the interaction of adaptation level and stimulus duration, were compared in a sample of 20 patients attending a glaucoma clinic using the visual field indices mean defect (MD), loss variance (LV), short-term fluctuation (SF) and corrected loss variance (CLV). LV and SF were greater with Octopus program 32 compared with Octopus program G1 (P < 0.02). No difference in the indices was found between stimulus sizes I and III for HFA program 30-2. MD was greater for program 30-2 compared with program 32 (P < 0.002) when expressed in terms of log (L/delta L) whereas LV (P < 0.02) and SF (P < 0.02) were greater for program 32. All differences were considered to be negligible in the clinical sense.