QUANTITATIVE ASSESSMENT OF FIXATIONAL EYE-MOVEMENTS BY SCANNING LASEROPHTHALMOSCOPY

A new method for quantifying fixational eye movements by scanning lase r ophthalmoscopy was developed and the method was evaluated in ten nor mal persons. Video sequences of the ocular fundus obtained during fixa tion were recorded, and linear movements of the fovea between successi ve video frames were transformed to angular movements of the eye by an algorithm that takes into account the individual optical properties o f the eye. A computer program was developed to automatically calculate the amplitude, the direction, and the duration of the angular movemen ts together with the precision of each of these estimates. Two types o f eye movements could be recognized in normal persons; a fast type (sa ccades) which was initiated and terminated within one video frame (20 msec), and a slow type (drifts) which lasted more than 8 video frames (160 msec). The mean amplitude of the fast movements (0.41 degrees) tv as significantly higher than the mean amplitude of the slow movements (0.31 degrees). The method was found to be suitable for quantifying fi xational eye movements in clinical trials while simultaneously visuali zing the ocular fundus. However, by refining the determination of the foveal position on the SLO images the precision of the method can be f urther improved.