Assessment of fixation stability in normal subjects and patients using a scanning laser ophthalmoscope

Abstract

1. In this study we have investigated the ability of normal and low vision subjects to (a) fixate stationary targets and (b) to maintain fixation on a stationary target while text was scrolled at different retinal locations. 2. Test stimuli were visualized directly on the fundus with the scanning laser ophthalmoscope (SLO), and relative eye movements were evaluated using digitized images. Target arrays consisted of single and multiple letters which were either stationary or scrolled in a horizontal direction. The retinal area selected by the subject to view the target was determined, and the stability of fixation calculated as a bivariate contour ellipse area (BCEA). 3. The ability to maintain steady fixation varied between individuals; this variability was particularly notable in the low vision patients. In the normal group, fixation was affected by the size of the stationary target but not by the form or polarity. In both the normal and patient groups stationary targets allowed more accurate fixation compared to scrolling text. The speed of scrolling text and the retinal location did not influence fixation stability.