It looks as if there is no eye here at all – we might call it anophthalmic. But a bit more investigation shows a microphthalmic globe underneath the third eyelid. Removal of this should give some vision in this eye, if not very much. Pigment is essential in showing developing cells where to go in the embryo, and this, at a very most basic level, is what makes white animals defective. In fact the Harlequin gene and the Merle gene cause sufficient problems when homozygous that HH embryos never survive and MM is a semi-lethal trait.