Crystalline Lens

The lens is a transparent structure in the eye that is suspended immediately behind the iris that brings rays of light to a focus on the retina. The crystalline lens is the name given to the natural lens that humans are born with. Small muscles attached to the lens can make the lens change shape, which allows the eyes to focus on near or far objects.

Elderly man examined by an ophthalmologist
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Also Known As: Crystalline lens

Functions of the Lens

The crystalline lens provides approximately one-third of the focusing power of the eye. The lens is flexible and its curvature can change by influence of the ciliary body. When it changes curvature, the lens gets thicker and the power increases so that the eye can focus on images at different distances. This change in focusing is called accommodation. When our eye looks at something at a very close distance to us, our ciliary body contracts and this loosens the lens zonules which hold the lens in place and the lens thickens. When the eye looks at images far away, the ciliary body relaxes, the lens zonules tighten back up and the lens decreases in thickness and this causes images far away to become in focus.

The Lens and Refraction

Refraction, or the bending of light inside the eye, occurs when light travels through lens. The light bends either outward or inward, depending on the lens. The lens then focuses images on the retina. If the lens causes the focus to occur behind the retina, farsightedness occurs. If the lens causes the focus to occur in front of the retina, nearsightedness occurs. Wearing glasses or contact lenses correct these vision problems. 

The Lens and Presbyopia

Over time, the lens loses some of its elasticity. This loss causes the eye to lose some of its ability to focus on near objects. This condition is known as presbyopia. At around the age of 40, most people require reading glasses. Presbyopia is often referred to as "short arm syndrome" because people tend to hold reading material out away from the body to read it more easily. People who have presbyopia may complain of needing more light to read. Presbyopic eyes also feel fatigued and seem to tire more easily. Some presbyopic patients may also have fluctuating vision, as their eyes are attempting to overcompensate for the vision deficit.

Cataract of the Lens

A cataract is a clouding of the lens. Cataracts often develop as we age making the lens cloudy. Fortunately cataracts grow slowly, and may not affect vision for several years. By age 65, over 90 percent of people have a cataract. 

Cataract treatment involves replacing the cloudy lens. By removing the cloudy lens, vision improves along with quality of life. Cataract surgery involves extracting the cataract and inserting a new, clear lens implant in its place. The procedure is usually performed under local anesthesia on an outpatient basis, taking less than an hour in most cases.

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