Variability in isopter position and fatigue during semi-automated kinetic perimetry

Background: Assessment of factors influencing response variability to repeat presentations of III4e stimuli and the fatigue effect during semi-automated kinetic perimetry (SKP). Design: Prospective case series; setting: university hospital. Participants: 58 patients with severe visual field loss: 21 with glaucoma, 18 with retinitis pigmentosa, and 19 with postchiasmal visual pathway lesions. Methods: Following initial testing with three isopters (I2e or V4e, I4e and III4e), presentations of the III4e stimulus were repeated four times during the same session along identical vectors. Main Outcome Measures: Variability in III4e-isopter position (scatter of kinetic threshold) and the difference of isopter area between the first and four subsequent sessions (fatigue effect) of SKP were analyzed by diagnosis, age, visual acuity and reaction time (RT). Results: The mean scatter of the kinetic threshold was 2.5 degrees (deg) in the glaucoma group, 1.5 deg in the group with retinitis pigmentosa, and 1.7 deg in the group of patients with postchiasmal lesions. The difference in the isopter area between a single examination and four times repeated examination was 656 square degrees (deg ²) in the glaucoma group, 104 deg ² in the retinitis pigmentosa group and 227 deg ² in the group of patients with postchiasmal lesions. Post-hoc regression analysis revealed that the variability of isopter position increased as the RT increased. Conclusion: The variability of III4e-isopter positionand fatiguewere most pronounced among glaucoma patients. RT is the most important factor influencing the variability of responses and fatigue during SKP, thus we propose that it can be used as a reliability indicator of SKP.