Cataracts

A cataract is a condition that affects a large percentage of the population. As a result, cataract surgery is the most common U.S. surgery performed. Currently, cataracts affect approximately 40 million people in the United States. Generally, the normal aging and cataractous changes in the lens are related to its metabolic activity. Acquired cataracts may be caused by penetrating trauma, irradiation, heat, or blunt trauma. Metabolic cataracts occur particularly in association with diabetes. Changes in the blood glucose concentration may alter the refractive power of the lens. With hyperglycemia, glucose byproducts enter the lens, causing it to swell and inducing a myopic shift. Nuclear sclerosis cataract is the most common cause of lens opacity seen by the ophthalmologist; an increased central density makes lens power stronger. As a result, frequent changes in the eyeglass prescription are necessary to correct the changing lens power. This type of cataract develops slowly, and surgery may not be necessary for several years.

The decision for cataract surgery with intraocular lens implantation depends on the degree of vision loss and the daily requirements of the patient. In patients with cataracts, indications for surgery include the patient's preference and needs, functional disability by Snellen visual acuity test and visual field testing, and concomitant ocular problems.

Cataract surgery involves removal of the cataractous lens and insertion of an intraocular lens. Generally, the procedure is performed under local anesthesia, although the patient may have general anesthesia. Modern cataract surgery primarily entails removing the lens through an extracapsular technique, which can be done en bloc or through a small corneal incision with phacoemulsification. In children, cataracts are generally soft and often require aspiration equipment.

Phacoemulsification is a technique that uses ultrasonic energy to break up the lens material so that it may be withdrawn through a small needle. Unfortunately, phacoemulsi-fication has been confused with laser treatment for cataract removal. It is important to emphasize to patients that the laser is not used to remove the cataractous lens. Part of the confusion lies in the fact that secondary cataracts or opacifi-cation of the posterior capsule can be eliminated using the YAG laser. With the YAG laser there is photodisruption of the capsule, which creates an opening and provides good visual acuity. Cataract removal is one of the most successful operations performed. Generally, adult patients are treated with intraocular lenses after cataract removal. If the patient has bilateral aphakia, contact lenses or cataract spectacles may be worn. However, moderate visual distortion occurs with aphakic spectacles, as well as restriction of peripheral vision. Routine preoperative testing does not improve clinical outcomes for healthy patients undergoing cataract surgery.

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