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Cataracts

 

Cataracts are often encountered and misunderstood in everyday practice.

A cataract is a cloudiness (opacity) in the eye's lens (purple structure in diagram below) that impairs vision.

 

Diagram of the eye

It is often confused with a pterygium (pronounced tih-ree-jum) - a fleshy growth of the conjunctiva onto the cornea (see image below).

Pterygium

Pterygium

Cataracts produce a progressive, painless loss of vision. Their cause is often not known, although they sometimes result from exposure to x-rays (such as high-dose radiotherapy to the eye), prolonged and strong sunlight, inflammatory eye diseases, certain drugs (such as corticosteroids), or complications of other diseases such as diabetes. They are more common in older people (65+); babies can be born with cataracts (congenital cataracts).

Symptoms

Because all light entering the eye must pass through the lens, any part of the lens that blocks, distorts, or diffuses light can cause poor vision - similar to looking through a bathroom window. How much vision deteriorates depends on where in the lens the cataract is and how dense (mature) it is.

In bright light, the pupil constricts, narrowing the cone of light entering the eye, so that it cannot easily pass around a central cataract. Thus, bright lights can be especially disturbing to many people with cataracts, who see haloes around lights, glare, and scattering of light. Such problems are particularly troubling when a person moves from a dark to a brightly lit space or tries to read with a bright lamp.

Surprisingly, a cataract in the central part of the lens (nuclear cataract) may improve vision at first. The cataract refocuses light, improving vision for objects close to the eye - it renders the eye more myopic (shortsighted) or less hyperopic (farsighted). Older people, who generally have trouble seeing things that are close, may discover that they can read again without glasses, a phenomenon often described as gaining 'second sight'. This is temporary, though.

Diagnosis and Treatment

A doctor can see a cataract while examining the eye with an ophthalmoscope (an instrument used to view the inside of the eye). Using an instrument called a slit lamp, a doctor can see the exact location of the cataract and the extent of its opacity.

The only way to treat a cataract is through surgical removal of the lens. People who have a cataract can determine when to have the surgery. When they feel unsafe, uncomfortable, or unable to perform daily tasks (usually visual acuity of 6/12 or worse), they may be ready for surgery. There is no great advantage to having surgery before then.

Before surgery, a person with a cataract can try other measures, such as spectacles and contact lenses which may possibly improve vision.

During the operation the lens is removed, and, most often, a new plastic or silicone lens is inserted; this artificial lens is called a lens implant. Without a lens implant, people usually need a contact lens. If they cannot wear a contact lens, they can try spectacles, which are very thick and tend to distort vision.

Cataract surgery is common and usually safe. To protect the eye from injury, the person wears glasses or a shield at night until healing is complete. The person visits the doctor the day after surgery and then typically every week or two for 6 weeks, after which a new spectacle prescription may be required.

Sometimes people develop an opacity behind a lens implant weeks or even years after it is implanted. Usually, such an opacity can be treated with a laser.