the species lacks a crystalline eye lens and has evolved a flat cornea. the combination of these traits makes the eye incapable of forming clear images on the retina and renders the dolphin effectively blind, but the eye may still serve as a light receptor. the retina contains a densely packed receptor layer, a very thin bipolar and ganglion cell layer, and a tiny optic nerve (with only a few hundred optic fibers) that are sufficient for the retina to act as a light-gathering component. although its eye lacks a lens (this species is also referred to as the "blind dolphin"), the dolphin still uses its eye to locate itself. the species has a slit similar to a blowhole on the top of the head, which acts as a nostril.