the dense pigmentation in the skin overlying the eye prevents light from reaching the retina from any entrance except for a pinhole sphincter-like structure. this structure is controlled by a cone-shaped muscle layer that extends from the posterior eye orbit to the overlying eye skin layer. the sphincter-like structure is capable of sensing light and may be able to sense the direction from where the light was emitted. however, the muddy waters, or low light conditions, that the "platanista gangetica" inhabit negate the use of the little vision that remains.