PAX6 and aniridia: This inefficiency may be caused directly by structural abnormalities related to altered PAX6 gene function (Free et al., 2003; Ellison-Wright et al., 2004) or by the ocular deficits associated with aniridia (e.g., poor visual acuity, cataract, glaucoma, foveal hypoplasia) which necessarily reduce the efficacy of functional input to the occipital lobe.