The most common cause of correctable vision loss, a cataract is a gradually developing opacity of the lens or lens capsule of the eye. Cataracts commonly occur bilaterally, with each progressing independently. Exceptions are traumatic cataracts, which are usually unilateral, and congenital cataracts, which may remain stationary. The prognosis is generally good; surgery improves vision in 95% of affected people.
Cataracts have various causes:
❑ Senile cataracts develop in elderly patients, probably because of degenerative changes in the chemical state of lens proteins.
❑ Congenital cataracts occur in neonates as genetic defects or as a sequela of maternal rubella during the first trimester. They acquire them through autosomal dominant inheritance, which will occur even if only one parent passes it along. Fifty percent of children in such families are affected.
❑ Traumatic cataracts develop after a foreign body injures the lens with sufficient force to allow aqueous or vitreous humor to enter the lens capsule. Trauma may also dislocate the lens.
❑ Complicated cataracts develop as secondary effects in patients with uveitis, glaucoma, or retinitis pigmentosa, or in the course of a systemic disease, such as diabetes, hypoparathyroidism, or atopic dermatitis. They can also result from exposure to ionizing radiation or infrared rays.
❑ Toxic cataracts result from drug or chemical toxicity with prednisone, ergot alkaloids, dinitrophenol, naphthalene, phenothiazines, or pilocarpine or from extended exposure to ultraviolet rays.
Cataracts occur as part of the aging process and are most prevalent in people older than age 70.
Characteristically, a patient with a cataract experiences painless, gradual blurring and loss of vision. As the cataract progresses, the normally black pupil appears hazy, and when a mature cataract develops, the white lens may be seen through the pupil. Some patients complain of blinding glare from headlights when they drive at night; others complain of poor reading vision, and of an unpleasant glare and poor vision in bright sunlight. Patients with central opacities report better vision in dim light than in bright light because the cataract is nuclear and, as the pupils dilate, patients can see around the lens opacity.
On examination, visual acuity is decreased, and the lens opacity remains unnoticeable until the cataract is advanced.
Treatment consists of surgical extraction of the cataractous lens opacity and intraoperative correction of visual deficits. The current trend is to perform the surgery as a same-day procedure. Surgical procedures include the following:
❑ Extracapsular cataract extraction (ECCE) removes the anterior lens capsule and cortex, leaving the posterior capsule intact. With this procedure, a posterior chamber intraocular lens (IOL) is implanted where the patient’s own lens used to be. (A posterior chamber IOL is currently the most common type used in the United States.) This procedure is appropriate for use in patients of all ages.
❑ Phacoemulsification uses ultrasonic vibrations to fragment and then emulsify the lens, which is then aspirated through a small incision.
❑ Intracapsular cataract extraction removes the entire lens within the intact capsule. This procedure is seldom performed today. ECCE with phacoemulsification has replaced it as the most commonly performed procedure.
❑ Discission and aspiration can still be used for children with soft cataracts, but this procedure has largely been replaced by phacoemulsification.
Infection is the most serious complication of intraocular surgery. Wound dehiscence can occur but is seldom a complication because of the small incision and minute sutures that are used. Hyphema, pupillary block glaucoma, and retinal detachment still occasionally occur.
The patient with an IOL implant may experience improved vision shortly after surgery if there’s no corneal or retinal pathology. Most IOLs correct for distance vision, but new IOLs are multifocal. However, the majority of patients will need either corrective reading glasses or a corrective contact lens, which will be fitted sometime between 4 and 6 weeks after surgery.
Where no IOL has been implanted, the patient may be given temporary aphakic cataract glasses; in about 4 to 8 weeks, he’ll be refracted for his own glasses.
Some patients who have an extracapsular cataract extraction develop a secondary membrane in the posterior lens capsule (which has been left intact), which causes decreased visual acuity. This membrane can be removed by the Nd:YAG laser, which cuts an area out of the center of the membrane, thereby restoring vision. Laser therapy isn’t used to remove a cataract.
Posterior capsular opacification occurs in approximately 15% to 20% of all patients within 2 years after cataract surgery.
After surgery to extract a cataract:
❑ Because the patient will be discharged after he recovers from anesthesia, remind him to return for a checkup the next day, and warn him to avoid activities that increase intraocular pressure such as straining.
❑ Urge the patient to protect the eye from accidental injury at night by wearing a plastic or metal shield with perforations; a shield or glasses should be worn for protection during the day.
❑ Before discharge, teach the patient to administer antibiotic ointment or drops to prevent infection and steroids to reduce inflammation; combination steroid-antibiotic eyedrops can also be used.
❑ Advise the patient to watch for the development of complications, such as a sharp pain in the eye uncontrolled by analgesics as a result of hyphema, or clouding in the anterior chamber (which may herald an infection), and to report them immediately.
❑ Caution the patient about activity restrictions, and advise him that it will take several weeks for him to receive his corrective reading glasses or lenses.
Read excerpts from these other book chapters related to Cataracts:
Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2008 Williams & Wilkins.
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Title: Professional Guide to Diseases (Eighth Edition)
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2005
ISBN: 1-58255-370-X
» Next page: Cataract (Handbook of Diseases)
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