Quantitative assessment of fixational eye movements by scanning laser ophthalmoscopy

A new method for quantifying fixational eye movements by scanning laser ophthalmoscopy was developed and the method was evaluated in ten normal persons. Video sequences of the ocular fundus obtained during fixation were recorded, and linear movements of the fovea between successive video frames were transformed to angular movements of the eye by an algorithm that takes into account the individual optical properties of the eye. A computer program was developed to automatically calculate the amplitude, the direction, and the duration of the angular movements together with the precision of each of these estimates. Two types of eye movements could be recognized in normal persons; a fast type (saccades) 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) was significantly higher than the mean amplitude of the slow movements (0.31 degrees). The methods was found to be suitable for quantifying fixational eye movements in clinical trials while simultaneously visualizing the ocular fundus. However, by refining the determination of the foveal position on the SLO images the precision of the method can be further improved.