The convex cornea and the convex crystalline lens of the human eye produce focused, real images which are inverted vertically and horizontally, because light rays cross over at the focal point of the combined cornea and lens.

The primate visual field is determined by the frontality of the eyes, by the protuberance of the eyes, and by the shape of the orbit.

The bilateral control of the upper facial muscles means that in the event of a lateral head injury, both eyes can still be closed.

Corollary discharge is necessary to distinguish movement of the eyes from movement of the world.