Abstract
Purpose: :
To measure the fixation stability (FS) of patients with mild to moderate amblyopia and to compare it to a group of controls with normal vision.
Methods: :
The eye positions were recorded simultaneously for the two eyes with a video-based eye tracker in three viewing conditions: binocular, monocular with the fellow eye viewing, and monocular with the amblyopic eye viewing. For the control participants, recording was binocular, monocular with the left eye viewing, and monocular with the right eye viewing. In the monocular conditions recording of the covered eye was done by means of an infrared filter. FS was quantified with a bivariate contour ellipse area (BCEA) which incorporates the variability of the horizontal and vertical eye positions.
Results: :
For the control participants, there were no differences between the two eyes and the best FS was obtained during binocular viewing. During monocular viewing, the FS of the viewing eye was worse than in binocular viewing (binocular summation) but was better than that of the covered eye (which was controlled by the innervation of the viewing eye but had no corrective visual feedback). For the patients with amblyopia, the best FS was obtained during binocular viewing with the fellow eye being significantly better that the amblyopic eye but not different from the controls. During monocular viewing when the fellow eye was the viewing eye, its FS was significantly better with binocular than with monocular viewing (binocular summation), comparable to the controls, and significantly better than the amblyopic eye’s. Finally, during monocular viewing when the amblyopic was the viewing eye, its monocular and binocular FSs were equivalent (i.e., there was no binocular summation for the amblyopic eye), and the FS of the fellow eye was not significantly different from that of the amblyopic eye.
Conclusions: :
The evaluation of FS in amblyopia should consider the binocular interactions between the two eyes. This technique for evaluating fixation stability allows us to separate the effects of binocular summation, monocular innervation and corrective visual feedback in amblyopia.
Keywords: amblyopia • eye movements • binocular vision/stereopsis