How Your Eyes Work

The eye is an approximately spherical bag of cells less than 1 inch in
diameter, which is filled with a pressured liquid. At the front is the
cornea, which is a window of transparent cells that allows light to
enter the eye. Behind the cornea is the iris, which is a diaphragm
of muscle that controls the amount of light entering the eye.

Behind the iris is the inner lens, which is a flexible capsule of
transparent cells. The ciliary muscle surrounds the lens and is
responsible for focusing the eye. When the ciliary muscle dilates,
it makes the inner lens thinner to focus on distant objects. When the
ciliary muscle constricts, it makes the inner lens thicker to focus on near
objects. In addition, six extraocular muscles surround each eyeball and responsible for moving the eyes.

The cornea and inner lens focus light onto the retina, which is a layer of cells at the back of the eye. The retina converts the light into electrical impulses that travel along the optic nerve to the brain, where they are enhanced by the visual cortex into what you actually see.