What Causes Cataracts?
In general, there are two main causes of cataracts: we can acquire them or we can be born with them.
Acquired Cataracts
A variety of factors cause acquired cataracts. Exposure to ultraviolet light and the normal process over time of the lens becoming less resilient, less transparent, and thicker can all contribute to the formation of cataracts.
Trauma to the eye can also cause cataracts and is the most common cause of cataracts in people under 40.
Systemic diseases can also cause cataracts, including diabetes and hypothyroidism.
Toxins, such as chronic use of corticosteroids, can cause cataracts. Several studies have linked the development of cataracts to alcohol consumption and exposure to cigarette smoke as well.(1)
Secondary causes, such as eye surgeries, chronic inflammation, and some types of glaucoma and extreme nearsightedness ( high myopia) can also cause cataracts to develop.
Congenital Cataracts
It is possible to be born with cataracts. These cataracts are known as congenital cataracts and are quite rare. About one-third of infants with congenital cataracts(2) have inherited cataracts.
Did You Know?
Cataracts are not caused by overuse of the eyes, and they cannot spread from one eye to the other, though we can develop cataracts in both eyes.
What Causes Cataracts – Medical Detail
Acquired Cataracts
Much like our skin, the lens of the eye is a type of epithelium. But unlike our skin, the lens cannot lose cells into the air. With age-related, nuclear cataracts, the nucleus of the lens becomes thicker as cells are sloughed off and deposited into the middle of the lens.
At the same time, the ciliary body's ability to provide nutrition to the lens contributes to the formation of a cataract.(2)
Trauma, such as a direct penetrating injury to the lens, a concussion, electric shock or lightning, or the use of irradiation to treat a tumor of the eye can all cause cataracts, usually posterior subcapsular cataracts.
Diabetes can cause cataracts by causing the lens to be overhydrated. When this occurs, deposits or opacities can form at either the front (anterior) or back (posterior) of the lens. In some cases, this type of cataract can form in a few days.
An endocrine disorder such as an over-active thyroid, or hypothyroidism, can cause cataracts as well.
Toxic cataracts are usually posterior subcapsular cataracts.
The most common cause of a secondary cataract is chronic inflammation of any of the components of the uvea, including the iris, the ciliary body, or choroids. (This inflammation is also known as chronic anterior uveitis.)
Other causes of secondary cataracts, such as surgery to treat glaucoma, vitreoretinal surgery, and retinal detachment and the subsequent surgery, can also cause a cataract to develop.
Acute congestive angle-closure glaucoma can also cause cataracts as can high myopia. Simple myopia does not predispose a person to develop cataracts, however.
In addition, hereditary fundus dystrophies such as retinitis pigmentosa, Leber congenital amaurosis, gyrate atrophy, Wagner and Stickler syndromes may also be associated with posterior subcapsular cataracts.
Congenital Cataracts
In addition to heredity, other causes of congenital cataracts include metabolic disorders such as galactosemia or hypoglycemia i and intrauterine infections such as rubella, herpes simplex, and varicela.
back to layman's descriptionDid You Know?
Acquired cataracts account for over 99 percent of all cataracts. Congenital cataracts account for less than 1 percent.
- (1) "The Aging Eye: A Special Health Report from Harvard Medical School," page 12. Ed. Fine, Laura C. M.D and Heier, , Jeffrey S. M.D., copyright 2006, Harvard Health Publications, Boston, MA.
- (2) Kanski, Jack J. Clinical Ophthalmology, 4th ed.
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