FATIGUE EFFECTS DURING A SINGLE SESSION OF AUTOMATED STATIC THRESHOLDPERIMETRY

Purpose. To determine using a routine clinical program the time course of the fatigue effect in both eyes at a given examination, the influe nce of rest periods during the examination, and the differences in the fatigue effect between persons with ocular hypertension and age-match ed normal subjects. Methods. Perimetry was undertaken for both eyes of 20 normal persons and 20 persons with ocular hypertension using Progr am G1X (Interzeag AG, Schlieren, Switzerland) of the Octopus 1-2-3 per imeter. Global mean defect and loss variance were calculated for each of the eight individual stages and global SF was calculated for stages 5 to 8. The superoinferior and nasotemporal hemifield indices and tho se for within and beyond 17 degrees eccentricity were calculated separ ately to investigate the locus of the fatigue effect. Results. Group m ean mean defect and loss variance deteriorated over stages (P < 0.001) and between eyes for both groups (P < 0.001; P < 0.004). The deterior ation in the mean defect was more marked peripherally (P < 0.001) and inferiorly with age and group (P < 0.001) whereas the localized loss w as more pronounced peripherally (P < 0.001), superiorly (P < 0.010) an d nasally (P < 0.001). A 1-minute break during the examination of a gi ven eye and a 3-minute break between eyes was insufficient to overcome the fatigue effect. The performance of the two groups was almost indi stinguishable. Conclusions. The deterioration in the visual field indi ces mean defect and loss variance challenges the currently accepted id eal length of a perimetric examination with the conventional algorithm s. Confidence limits for the definition of abnormality with these algo rithms should reflect the presence of the fatigue effect and be differ ent for the second eye.