Rods are located in every part of the retina except the fovea centralis, which is where the cones that allow us to see most colors and detail are located. Rods are responsible for our peripheral vision, and are very sensitive to motion. Rods do not provide very good spatial differentiation, but their sensitivity to light is essential to providing definition.

The ciliary muscle surrounds the lens in a circular fashion. When contracted, the ciliary muscle will decrease in size, which allows the lens to become more convex in shape. This allows the eye to focus on closer objects.

The iris, or pupillary sphincter, is capable of constricting and dilating the pupil. The main muscle responsible for raising the eyelid is the levator palpebrae superioris. The orbicularis oculi is responsible for closing the eyelid.