Eccentric fixation in amblyopia: is reduced foveal acuity the cause?

The Worth-Chavasse theory of amblyopia is briefly reviewed with particular attention to Worth's explanation that eccentric fixation develops in an attempt by the amblyopic eye to fixate with an eccentric retinal locus having higher acuity than the fovea. Three experiments are reviewed; these show that of 8 eccentrically fixating amblyopic eyes tested, 7 had foveal acuity that was higher than or equal to the acuity at the eccentric fixation locus. A fourth study is reviewed, however, which reports that 24 of 25 eccentrically fixating amblyopic eyes had highest acuity at the eccentric retinal locus. With only slight reservations, the conclusion from the first 3 experiments that eccentric fixation does not occur to improve acuity appears justified, but the contrary results of the fourth study, in which fixation was not controlled, cannot easily be dismissed. The importance of performing an experiment that accurately measures acuity across the retinas of amblyopic eyes with careful control of fixation and target location is stressed.