What Are the Functions of the Lens in the Eye?
The ability of the human eye to "see" is interdependent upon all of its parts. The purpose of the lens is to focus objects near and far to make them clear. The lens, like the lens of a camera, opens and shuts to allow light to reach the retina to focus an image. With age, the lens loses the function to refract light to bring images into focus. Disease can rob the lens of its function to work with light. Many conditions can be corrected with surgery.
Location
The lens sits behind the colored part of the eye (the iris) that circles the black pupil. Extensions of an encircling ring of muscle hold the lens in position behind the cornea, the iris and the pupil. Dividing the eye into two main chambers, the iris and lens form a front area full of a watery liquid called the aqueous humor. The back chamber is filled with a jellylike material, the vitreous body.
Cornea, Pupil and Lens
Light entering the eye first passes through the outer clear layer called the cornea. Bending from the curvature of the corneal plane, the light then enters through the pupil. The pupil controls the amount of light that passes through the cornea and the lens.
Ciliary Muscles and the Lens
The ciliary muscles flatten the lens when they tense, and make it more spherical--increase the diameter--when they relax. This movement enables the lens to adjust the focus of far and near objects in relationship to one another.
Age Effects
Aging causes the lens and the soft material encasing it--the cortex--to harden. This lessens the ability of the lens to change shape to adjust for close or distance vision. This function of the lens is called accommodation.
Diseases
Cataracts are a condition that often comes with age. Cataracts form when protein clumps together in the lens, clouding it. Left medically unattended, cataracts eventually cause irreversible blindness. Caught in early stages of development, surgically removing these cataracts restores the patient's sight. In cataract surgery, the old lens is removed and an artificial lens is inserted. This is a common and relatively painless procedure.
Presbyopia occurs with normal aging and is a gradual loss of the eye's ability to adjust the focus on what it sees. With presbyopia the lens stiffens and disrupts how the eye sees near objects. Commonly diagnosed in people around the age of 40, prescribing reading glasses or bifocals corrects presbyopia.
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