Scotoma mapping by semi-automated kinetic perimetry: The effects of stimulus properties and the speed of subjects' responses

Purpose: The study aimed firstly to determine the effects of stimulus variables on the detection of a scotoma border and, secondly, to study the reproducibility of the method during semi-automated kinetic perimetry. Methods: The size of the physiological blind spot in 18 young normal subjects was measured with a video-campimetric device, the Tübingen computer campimeter (TCC). Kinetic stimuli of two different sizes and at four different levels of luminance were presented. Examinations were repeated within 2 weeks. Measurements were corrected for individual response times and the area of the blind spot was computed. The effects of stimulus strength and size and the repeatability of blind spot measurements were evaluated by an analysis of variance. Results: The physiological blind spot showed significant inter- and intraindividual variations in size (least square means ranging from 17 to 49 square degrees), with a standard deviation of 6.8 square degrees. The measured size of the blind spot increased as a function of decreasing stimulus value, by reducing either the relative brightness or the size of stimuli. Use of a correction for each subject's speed of responses nearly halved the level of random variance. The temporal sequence of measurements (the order in which they were performed) had no apparent effect on the calculated values of blind spot size. Conclusions: Semi-automated kinetic perimetry can determine the size of the physiological blind spot with good repeatability in young, normal subjects. Determination of each individual's speed of response and inclusion of this variable in the calculations reduced variance of the measure significantly. This study confirmed the presence of considerable interindividual differences in the size of the physiological blind spot.