Lens of the Eye: Structure, Functions, and Diseases

The lens of the eye is a transparent body inside the eyeball that works as a biological lens and conducts light to the retina. With age, the tissues of the lens change, and then we speak of diseases of the lens of the eye, the best known of which is cataract.

What the lens of the eye is

The lens, or crystalline lens, is located between the vitreous body and the iris. It is a transparent biconvex rounded elastic formation that is attached by thin fibers of the zonule of Zinn to the ciliary body — a muscle that changes its shape. It has no vessels or nerves; its nutrition comes from the vitreous body and the aqueous humor. In an adult, the thickness of the lens is approximately 3.6 to 5 millimeters, and the diameter is about 9–10 millimeters.

Structure of the lens

The capsule, the capsular epithelium, and the main substance are distinguished. The capsule is a thin elastic transparent membrane that protects the lens and strongly refracts light; it is thicker in front than behind. Beneath the anterior capsule lies a single layer of epithelial cells: it nourishes the lens, gives rise to new fibers, and serves as a barrier. The bulk is formed by fibers — elongated cells in the form of transparent hexagonal prisms made of the protein crystallin. Young fibers push older ones toward the center, and in this way a dense nucleus is formed, surrounded by a softer cortex; its density increases over the years, and by about age 45 the ability to focus at close range decreases in people with normal vision.

What function the lens performs

The main job of the lens is to focus light: it gathers rays and directs them onto the retina. Until about age 45 it changes shape, so the gaze moves freely from a distant object to a near one; this adjustment is called accommodation. With age, the proteins of the lens break down, it becomes less flexible, and focusing at near distances becomes difficult. Its second task is protection: it absorbs ultraviolet radiation in the range from 300 to 400 nanometers and protects the retina from damage.

Diseases of the lens of the eye

The main disease of the lens is cataract, that is, clouding. Normally the lens is transparent; with cataract it becomes cloudy, light is scattered, and vision gradually declines to the point of loss. The process is slow and painless, usually in both eyes, but the severity differs. Mild clouding often appears after age 60, and by age 75 most people have cataract. The signs are as follows:

• blurriness, haze, or a veil before the eye at any distance;
• difficulty in low light and at night, sensitivity to light and glare;
• halos around light sources and double vision of objects;
• fading of colors, especially blue;
• frequent changes of glasses.

The lens becomes cloudy because of age-related breakdown of proteins in the fibers, and the process is accelerated by diabetes, inflammation of the eye, trauma and eye surgery, long-term oral corticosteroids, radiation, smoking, sun without protection, and heredity. The risk is higher after age 60, in women, with marked myopia, type 2 diabetes, severe dermatitis, and high blood pressure. A rare complication is hypermature cataract: its masses leak into other parts of the eye and can cause a painful form of glaucoma and inflammation.

How the condition of the lens is checked

A standard examination by an ophthalmologist is usually sufficient: the eye is viewed through a slit lamp — a device that produces a thin beam of light in which clouding of transparent media can be seen. Other examinations are rarely needed. If the clouding does not yet interfere with life, the doctor may limit treatment to new glasses, brighter light for reading, and sunglasses. Cataract can be removed only by surgery with replacement of the lens with an artificial one, and it is discussed when vision interferes with driving, reading, or working at a screen.

When to see an ophthalmologist

The reason for a visit is any change in vision: blurriness, poor visibility at night, blinding light, halos around lamps, dulled colors, too frequent changes of glasses. It is enough to make an appointment with an ophthalmologist: they will decide whether additional tests and observation are needed.

Clouding of the lens is not in itself a reason to call an ambulance. The numbers 103 and 112 are needed if severe pain in the eye is added to the decline in vision: advanced cataract can cause a painful form of glaucoma and inflammation inside the eye.

To return to the main point: the lens is transparent and therefore unnoticed, and its clouding does not hurt — it simply takes away vision, and changes can be noticed earlier, at an examination. The material is for reference and does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer