Structure of the eye.

The sclera is the white outer layer of connective tissue.

At the front, the sclera becomes the transparent cornea, letting light into the eye.

The iris regulates amount of light entering the pupil, the hole in the center of the iris.

The iris is part of the choroid, a thin layer of pigmented cells.

The lens focuses light on the retina.

The retina lies inside the choroid and contains photoreceptors.

The fovea is the center of the visual field with a high concentration of cone cells.

Signals leave the eye at the optic disk (blind spot ) to the optic nerve.