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Cataracts - Introduction

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of cataracts.

Introduction:

A cataract is an opacity, or clouding, of the lens of the eye.

The lens of an eye is normally clear. If the lens becomes cloudy or is opacified, it is called a cataract.

The prevalence of cataracts increases dramatically with age. It typically occurs in the following way:

The lens is an elliptical structure that sits behind the pupil and is normally transparent. The function of the lens is to focus light rays into images on the retina (the light-sensitive tissue at the back of the eye).
In young people, the lens is elastic and changes shape easily, allowing the eyes to focus clearly on both near and distant objects.
As people reach their mid-40s, biochemical changes occur in the proteins within the lens, causing them to harden and lose elasticity. This causes a number of vision problems. For example, loss of elasticity causes presbyopia, or far-sightedness, requiring reading glasses in almost everyone as they age.
In some people, the proteins in the lens, notably those called alpha crystallins, may also clump together, forming cloudy (opaque) areas called cataracts. They usually develop slowly over several years and are related to aging. In some cases, depending on the cause of the cataracts, loss of vision progresses rapidly.
Depending on how dense they are and where they are located, cataracts can block the passage of light through the lens and interfere with the formation of images on the retina, causing vision to become cloudy.

Eye
Click the icon to see an image of eye anatomy.

Cataracts can form in any of three parts of the lens and are named by their location.

Nuclear cataracts. These form in the nucleus (the inner core) of the lens. This is the most common variety of cataract associated with the aging process.
Cortical cataracts. These form in the cortex (the outer section of the lens).
Posterior subcapsular cataracts. These form toward the back of a cellophane-like capsule that surrounds the lens. They are more frequent in people with diabetes, who are overweight, or those taking steroids.

Resources

www.ascrs.org -- The American Society of Cataract and Refractive Surgery
www.aao.org -- American Academy of Ophthalmology
www.nei.nih.gov -- National Eye Institute
www.eyesurgeryeducation.com -- Eye Surgery Education Council
www.lighthouse.org -- Lighthouse International
www.aao.org/aao/find_eyemd.cfm -- Find an ophthalmologist

References

Allen D. Cataract. BMJ Clinical Evidence. Web publication date: 01 April 2007 (based on October 2006 search). Accessed July 1, 2008.

American Academy of Ophthalmology. Cataract in the Adult Eye, Preferred Practice Pattern. San Francisco: American Academy of Ophthalmology, 2006. Accessed July 1, 2008.

Awasthi N, Guo S, Wagner BJ. Posterior capsular opacification: a problem reduced but not yet eradicated. Arch Ophthalmol. 2009 Apr;127(4):555-62.

Bell CM, Hatch WV, Fischer HD, Cernat G, Paterson JM, Gruneir A, et al. Association between tamsulosin and serious ophthalmic adverse events in older men following cataract surgery. JAMA. 2009 May 20;301(19):1991-6

Clinical Trial of Nutritional Supplements and Age-Related Cataract Study Group, Maraini G, Sperduto RD, Ferris F, Clemons TE, Rosmini F, et al. A randomized, double-masked, placebo-controlled clinical trial of multivitamin supplementation for age-related lens opacities. Clinical trial of nutritional supplements and age-related cataract report no. 3. Ophthalmology. 2008 Apr;115(4):599-607.e1.

Fernandez MM, Afshari NA. Nutrition and the prevention of cataracts. Curr Opin Ophthalmol. 2008 Jan;19(1):66-70.

Friedman AH. Tamsulosin and the intraoperative floppy iris syndrome. JAMA. 2009 May 20;301(19):2044-5.

Guercio JR, Martyn LJ. Congenital malformations of the eye and orbit. Otolaryngol Clin North Am. 2007 Feb;40(1):113-40, vii.

Long V, Chen S, Hatt S. Surgical interventions for bilateral congenital cataract. Cochrane Database Syst Rev. 2006 Jul 19;3:CD003171.

Moeller SM, Voland R, Tinker L, Blodi BA, Klein ML, Gehrs KM, et al. Associations between age-related nuclear cataract and lutein and zeaxanthin inthe diet and serum in the Carotenoids in the Age-Related Eye Disease Study, an Ancillary Study of the Women's Health Initiative. Arch Ophthalmol. 2008 Mar;126(3):354-64.

Olitsky SE, Hug D, and Smith LP. Abnormalities of the lens. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. St. Louis, MO: WB Saunders; 2007; chap 627.

Wishart MS, Dagres E. Seven-year follow-up of combined cataract extraction and viscocanalostomy. J Cataract Refract Surg. 2006 Dec;32(12):2043-9.

Reviewed last on: 6/23/2009
Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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