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Aging-Related Diseases Eye - Cataracts

age physiological clinical lens changes surgery tissue

A cataract is a clinical condition that describes the opacification (clouding) of the natural lens of the eye. A cataract is not a growth, but a change in the tissue structure of the lens. These changes are very much age-related, and almost physiological, although they occur at much younger ages in some patients than in others, and there are also many ways in which the tissue changes. The most common and physiological change, described as sclerosis of the lens, is similar to a yellowing of plastic after many years of exposure to sunlight. This type of cataract often improves near vision because it helps magnify items, but it reduces distance vision.

Other types of cataracts appear in a spoke-like fashion in the lens or in a membrane type of opacification known as a posterior subcapsular cataract. In all types of cataracts, vision, usually for distance and near, is reduced. Patients often have problems with glare from sunlight, and streetlights and car headlights, and eventually their quality of life deteriorates. As these changes occur, changes in the refractive error, or the power that is needed for eyeglasses, also changes, and in the early stages, a change in lenses can compensate for some of the changes in the eye. Eventually, however, this no longer suffices and more drastic therapy is needed.

Because the lens is an isolated structure with no blood vessels, it has long been known that it could be removed, rather safely, from the eye. Current cataract techniques are called removal by phacoemulsification, and introduction of an intraocular lens. Phacoemulsification is a technique in which a very high-frequency ultrasound probe is introduced into the lens. The lens tissue is then pulverized, as it were, and a second system sucks out the material so that the lens tissue is removed completely from its very thin membranous sac, known as the capsule. An intraocular lens is then inserted to replace the natural lens. The current standard is to insert a lens that has been folded on itself and will unfold in the eye when it is in place. These techniques allow cataract surgery to be done through a 3 millimeter incision in the clear part of the cornea, and does not require any stitching. Healing is more rapid and safe with this technique. Currently, cataract surgery is an outpatient procedure with only numbing drops put on the eye rather than any other anesthesia or medication being used.

The cataract surgery is one of the great surgical success stories of the late twentieth century. It has permitted millions of people the world over to be rehabilitated to a more functional status and a better quality of life. Nonetheless, cataracts remain the number one cause of blindness in the developing world, and it is simply a matter of resources to get enough cataract surgery done in the developing world to reverse that statistic.

RAYMOND LEBLANC KENNETH ROCKWOOD

BIBLIOGRAPHY

BUCH, H.; VINDING, T.; and NIELSEN, N. V. "Prevalence and Causes of Visual Impairment According to World Health Organization and United States Criteria in an Aged, Urban Scandinavian Population: The Copenhagen City Eye Study." Ophthalmology 108 (December 2001): 2347–2357.

JAENICKE, R., and SLINGSBY, C. "Lens Crystallins and Their Microbial Homologs: Structure, Stability, and Function." Critical Reviews in Biochemistry and Molecular Biology 36 (2001): 435–499.

LICHTER, P. R.; MUSCH, D. C.; GILLESPIE, B. W.; GUIRE, K. E.; JANZ, N. K.; WREN, P. A.; MILLS, R. P.; and the CIGTS Study Group. "Interim Clinical Outcomes in the Collaborative Initial Glaucoma Treatment Study Comparing Initial Treatment Randomized to Medications or Surgery." Ophthalmology 108 (2001): 1943–1953.

YI, Q.; FLANAGAN, S. J.; and MCCARTY, D. J. "Trends in Health Service Delivery for Cataract Surgery at a Large Australian Ophthalmic Hospital." Clinical and Experimental Ophthalmology 29 (October 2001): 291–295.

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