The purpose of the eye is to form a clear image of the object being viewed on the retina, and then to pass this to the brain for processing. The human eye, like a camera, does this with lenses. The cornea, the clear window at the front of the eye, does most of the focusing work. The light passes through the pupil which controls the amount of light entering the eye and is then focused further by the lens inside the eye.

 

This lens is flexible and can be made fatter or thinner to give more or less focusing power to view near and far objects. To bring a distant object into focus the circular ciliary muscle relaxes against the wall of the eye, pulling the suspensory ligament to stretch the lens into a flatter, thinner form. For close focusing the ciliary muscle contracts, slackening the suspensory ligament and allowing the lens to return to a fatter, more rounded shape.

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