A common cause of 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.
Cataracts are a part of aging and are most prevalent in patients older than age 70. Surgical intervention improves vision in 95% of affected people.
Cataracts have various causes, depending on their type:
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 result of maternal rubella during the 1st trimester.
Traumatic cataracts develop after a foreign body injures the lens with sufficient force to allow aqueous or vitreous humors to enter the lens capsule.
Complicated cataracts develop as secondary effects in patients with uveitis, glaucoma, retinitis pigmentosa, or a detached retina or in the course of a systemic disease, such as diabetes, hypoparathyroidism, or atopic dermatitis. These cataracts can also result from exposure to ionizing radiation or infrared rays.
Toxic cataracts result from prolonged drug or chemical toxicity from prednisone, ergot alkaloids, naphthalene, or phenothiazines; they also result from excessive exposure to sunlight.
Signs and symptoms
Characteristically, a patient with a cataract experiences painless, gradual blurring and loss of vision. As the cataract progresses, the normally black pupil turns milky white (in extreme cases). Otherwise, lens opacity is revealed during a slit-lamp examination.
Some patients complain of blinding glare from headlights when they drive at night; others report an inability to recognize people or things at a distance. 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.