The locus of fixation in strabismic amblyopia changes with increasing effort of recognition as assessed by scanning laser ophthalmoscope.

PURPOSE We performed a qualitative assessment of fixation behaviour in relation to the fovea in patients with strabismic amblyopia. METHODS The fixation of 25 patients with strabismic amblyopia was examined using a scanning laser ophthalmoscope (SLO). A digital frame grabber board was programmed to scan onto the patient's retina single solid black discs of 5, 10 and 15 degrees in diameter and Landolt Cs in different orientations and corresponding to a visual acuity (VA) of 0.01-0.2 in European decimals. The relative position of the fovea was video-recorded. Fifty video fields per second were plotted as x/y (fixational positions in relation to the fovea) and x/t (motion over time) graphs. RESULTS Three main groups of patients were seen. Group 1 (n = 6), with a VA of < 0.1, showed a grossly eccentric and unstable locus of fixation independent of size/type of test stimulus used. Group 2 (n = 15), with VA of 0.1-0.8, initially used an eccentric retinal area for fixation that, however, shifted to the fovea with decreasing size and increasing detail of the target for fixation. Group 3 (n = 4), with VA of 0.3-0.8, had stable central fixation throughout. CONCLUSIONS We speculate that the reduced VA associated with strabismic amblyopia is due to a defective motor control of fixation that can be modulated by recognitional effort.