Treatment of eccentric fixation by the use of a red filter.

THE treatment of amblyopia and eccentric fixation is said to be associated with special problems. In some centres pleoptics have been used, but the need for trained staff and special equipment can pose difficult problems. The harmful effects of conventional occlusion of the fixing eye have been stressed by Arruga (1962). Recently, Brinker and Katz (1963) have drawn attention to the fact that, as the fovea contains only cones, a red filter placed before the eye with non-central fixation while the dominant eye is occluded, may have the effect of inducing central'fixation by preferential stimulation of the fovea. This is because under red illumination only the photopic mechanism is active so that the cones of the fovea should be preferentially stimulated. However, Scully (1961) and von Noorden (1965) have pointed out that in many cases of eccentric fixation occlusion of the dominant eye does in fact lead to central fixation in the affected eye. In the present study, occlusion of the conventional type was compared with occlusion using the red filter in patients with eccentric fixation. Because the dangers of conventional occlusion have been so often stressed in such cases, it was decided that all patients should be given one month's inverse occlusion to the eccentric eye, before starting occlusion of the dominant eye, regardless of whether red filter treatment was subsequently used or not.