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May 20, 2012 |
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A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light. Early in the development of age-related cataract the power of the lens may be increased, causing near-sightedness ( myopia), and the gradual yellowing and opacification of the lens may reduce the perception of blue colours. Cataracts typically progress slowly to cause vision loss and are potentially blinding if untreated. The condition usually affects both the eyes, but almost always one eye is affected earlier than the other. A senile cataract , occurring in the elderly, is characterized by an initial opacity in the lens, subsequent swelling of the lens and final shrinkage with complete loss of transparency. Moreover, with time the cataract cortex liquefies to form a milky white fluid in a Morgagnian cataract , which can cause severe inflammation if the lens capsule ruptures and leaks. Untreated, the cataract can cause phacomorphic glaucoma . Very advanced cataracts with weak zonules are liable to dislocation anteriorly or posteriorly. Such spontaneous posterior dislocations (akin to the historical surgical procedure of couching ) in ancient times were regarded as a blessing from the heavens, because some perception of light was restored in the cataractous patients. Cataract derives from the Latin cataracta meaning "waterfall" and the Greek kataraktes and katarrhaktes , from katarassein meaning "to dash down" ( kata -, "down"; arassein , "to strike, dash"). As rapidly running water turns white, the term may later have been used metaphorically to describe the similar appearance of mature ocular opacities. In Latin, cataracta had the alternate meaning " portcullis", so it is also possible that the name came about through the sense of "obstruction". Early Persian physicians called the term nazul-i-ah , or "descent of the water"???vulgarised into waterfall disease or cataract???believing such blindness to be caused by an outpouring of corrupt humour into the eye. Age-related cataract is responsible for 48% of world blindness, which represents about 18 million people, according to the World Health Organization (WHO). In many countries surgical services are inadequate, and cataracts remain the leading cause of blindness. As populations age, the number of people with cataracts is growing. Cataracts are also an important cause of low vision in both developed and developing countries. Even where surgical services are available, low vision associated with cataracts may still be prevalent, as a result of long waits for operations and barriers to surgical uptake, such as cost, lack of information and transportation problems. In the United States, age-related lenticular changes have been reported in 42% of those between the ages of 52 to 64, 60% of those between the ages 65 and 74, and 91% of those between the ages of 75 and 85. The increase in ultraviolet radiation resulting from depletion of the ozone layer is expected to increase the incidence of cataracts. The earliest records are from the Bible as well as early Hindu records. Early cataract surgery was developed by the Indian surgeon , Sushruta (6th century BCE). The removal of cataract by surgery was also introduced into China from India. The first references to cataract and its treatment in Ancient Rome are found in 29 CE in De Medicinae , the work of the Latin encyclopedist Aulus Cornelius Celsus. The Romans were pioneers in the health arena???particularly in the area of eye care. The Muslim ophthalmologist Ammar ibn Ali of Mosul performed the first extraction of cataracts through suction. He invented a hollow metallic syringe hypodermic needle, which he applied through the sclera and extracted the cataracts using suction. In his Choice of Eye Diseases , written circa 1000 CE, he wrote of his invention of the hypodermic needle and how he discovered the technique of cataract extraction while experimenting with it on a patient. The following is a classification of the various types of cataracts. This is not comprehensive and other unusual types may be noted.
As a cataract becomes more opaque, clear vision is compromised. A loss of visual acuity is noted. Contrast sensitivity is also lost, so that contours, shadows and color vision are less vivid. Veiling glare can be a problem as light is scattered by the cataract into the eye. The affected eye will have an absent red reflex. A contrast sensitivity test should be performed and if a loss in contrast sensitivity is demonstrated an eye specialist consultation is recommended. In the developed world, particularly in high-risk groups such as diabetics, it may be advisable to seek medical opinion if a 'halo' is observed around street lights at night, especially if this phenomenon appears to be confined to one eye only. The symptoms of cataracts are very similar to the symptoms of ocular citrosis. Cataracts may be partial or complete, stationary or progressive, hard or soft. Some drugs can induce cataract development, such as corticosteroids and Seroquel. There are various types of cataracts, e.g. nuclear, cortical, mature, and hypermature. Cataracts are also classified by their location, e.g. posterior (classically due to steroid use) and anterior (common (senile) cataract related to ageing). Associations with systemic conditions
Although cataracts have no scientifically proven prevention, it is sometimes said that wearing ultraviolet-protecting sunglasses may slow the development of cataracts. Regular intake of antioxidants (such as vitamin A, C and E) is theoretically helpful, but taking them as a supplement has been shown to have no benefit. The less well known antioxidant N-acetylcarnosine has been shown in randomized controlled clinical trials to treat cataracts, and can be expected to prevent their formation by similar mechanisms. N-acetylcarnosine is a proposed treatment for other ocular disorders that are instigated, or exacerbated by oxidative stress including glaucoma, retinal degeneration, corneal disordes, and ocular inflammation. When a cataract is sufficiently developed to be removed by surgery, the most effective and common treatment is to make an incision ( capsulotomy ) into the capsule of the cloudy lens in order to surgically remove the lens. There are two types of eye surgery that can be used to remove cataracts: extra-capsular (extracapsular cataract extraction, or ECCE) and intra-capsular (intracapsular cataract extraction, or ICCE). Extra-capsular (ECCE) surgery consists of removing the lens but leaving the majority of the lens capsule intact. High frequency sound waves ( phacoemulsification) are sometimes used to break up the lens before extraction. Intra-capsular (ICCE) surgery involves removing the entire lens of the eye, including the lens capsule, but it is rarely performed in modern practice. In either extra-capsular surgery or intra-capsular surgery, the cataractous lens is removed and replaced with a plastic lens (an intraocular lens implant) which stays in the eye permanently. Cataract operations are usually performed using a local anaesthetic and the patient is allowed to go home the same day. Recent improvements in intraocular technology now allow cataract patients to choose a multifocal lens to create a visual environment in which they are less dependent on glasses. Under some medical systems multifocal lenses cost extra. Traditional intraocular lenses are monofocal. Complications are possible after cataract surgery, including endophthalmitis, posterior capsular opacification and retinal detachment. Research is scant and mixed but weakly positive for the nutrients lutein and zeaxanthin. Bilberry extract shows promise in rat models and in clinical studies. Investigational TreatmentsIn the past few years, eye drops containing acetyl-carnosine have been used by several thousands cataract patients across the world. The drops are believed to work by reducing oxidation and glycation damage in the lens, particularly reducing crystallin cross-linking. Randomized controlled trials indicate the drops may be especially appropriate for seniors, or others where surgery is not advised. Investigational preventivesAlthough statins are known for their ability to lower lipids, they are also believed to have antioxidant qualities. It is believed that oxidative stress plays a role in the development of nuclear cataracts, which are the most common type of age-related cataract. To explore the relationship between nuclear cataracts and statin use, a group of researchers took a group of 1299 patients who were at risk of developing nuclear cataracts and gave some of them statins. Their results suggest that statin use in an at-risk population may be associated with a lower risk of developing nuclear cataract disease. Long term (avg 5 year) observation showed that systematic application of azapentacene sodium polysulfonate (Quinax) slows down the progress of the disease.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Cataract".
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