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Causes:
1) Aging
The explanation lies on a normal part of our metabolism occurring throughout the body, oxidation. The sources of oxidation, or oxidative stress, include ultraviolet radiation ( UV light ), x-radiation ( X ray ), and the cosmic radiation to which the astronauts are exposed. As the posterior part of the eye is so transparent, the lens is
constantly bathed in light, including UV light, and over years of time the delicate protein arrangement in the lens gets damaged and transparency suffers and vision becomes blurred. With evidence, it is found that the oxidative process releases chemicals called free radicals. In the aqueous humor, which nourishes and surrounds the lens, free radicals such as hydrogen peroxide is formed causing for loss of transparency and cataract formation.
2) Long duration of diabetes
Diabetes, a disorder characterized by elevated blood sugar levels, is proved to increase the juvenile's chance of having cataracts. It is discovered that 2 aldose sugars, glucose and galactose, have a direct effect on human cataract formation. These sugars dissolve into the lens of diabetic and are converted into substances that causes the lens to swell rapidly with the aqueous humor. This bloating of lens upsets the balance to keep it clear, resulting in dense cataract. The whole process is seemingly caused by the culprit -- aldose reductase which is triggered by high levels of sugar in the eye.
3) Injury to lens
Cataract may develop from an injury to the eye, either one in which an object
penetrates the eye and touches the delicate clear lens or one that jars the lens enough to damage it. This type of cataract is called TRAUMATIC CATARACT.
4) Congenital
There a many causes of congenital cataracts; the common denominator is something the interferes with the normal development of the lens in the fetus. Premature babies will usually have a higher chance of having congenital cataract than full-term babies. Medications taken by mother during pregnancy, especially cortisone-type drugs and certain tranquilizers, are prone to congenital cataract. German measles or rubella infection during the last part of the first three months of pregnancy, can seriously affect the developing eye, causing congenital cataracts in the majority cases.
5) Glass blowers
This is due to the exposure to intense heat, electric shock and electroconvulsion shock treatment
6) Other eye disease
Even other eye diseases such as iritis, an inflammation of the iris, can lead to cataracts. Cataracts developed from other eye diseases are called SECONDARY CATARACTS.
7) Dehydration
In the third world countries, life-threatening diarrhea and dehydration have been definitely implicated in causing cataracts.
8) Low levels of calcium
Although insufficient calcium can also lead to cataracts, the main cause is not low intake or calcium but the malfunctioning of the four glands in the neck, the parathyroid glands, which regulates the level of calcium in the blood.
9) Continuous doses of cortisone for prolonged periods
Several illnesses, such as arthritis, asthma, gastro-interstinal disorders, and autoimmune-type diseases such as lupus, are often treated by cortisone. The cortisone causes a specific type of opacification of the back part of the lens just under the capsule.
10) Cigarette smoking
This is probably the latest possible cause of cataracts in an increasingly long list. Studies have shown that cigarette smokers more than doubled their risk of developing cataracts than non-smokers.
Symptoms:
1) Diminished Vision
This is the most common symptom of cataract. It may be subtle or gradual. The degree to which one notices this symptom varies, depending on the patient's sensitivity to a change in vision. It starts with a vague, nagging feeling, a slight suspicion in having problem with one's sight. At this initial point, there may be no supporting objective findings.
2) Double Vision
It may not necessarily be caused by a true cataract, it may be because of an eye-muscle problem. In case of cataracts, it is caused by the difference in opacities of the different part of the lens, as the rays of light split into two or even three parts. This is especially true of a small cataract in the nucleus.
3) Newly acquired ability to read without glasses
This symptom may be the earliest and the only clue to the presence of a developing cataract. The explanation lies in the part of the lens first affected by the cataractous process. When the cataract starts in the central nuclear
area of lens, the nucleus will become sclerotic or hard. The lens will then get fatter and optically stronger, causing light to be focused in front of the retina. The net effect on the eye is that it becomes nearsighted, causing near objects to be in focus even without using glasses.
4) Frequent changes in eyeglass prescription
The same explanation, nearsightedness, is applied. As the cataract increases ones nearsightedness, the eyeglass prescription needs to be kept in pace with the changes with one's eye.
5)Poor vision in bright light and improved vision in dim light
This may seem to be an illogical symptom, but it is true, depending on the type of cataract and which part of the lens is affected. When most of the clouding is centered on the back or posterior surface of the lens, the cataract will have its greatest impact when the pupil is small. When there is bright light, the small pupil corresponds in size and shape to the clouded center of the lens, therefore the vision will be quite blurred. The brighter the light, the smaller the pupil, and the situation will be worse. This type of cataract, called POSTERIOR SUBCAPSULAR CATARACT ( PSC ), is more common
in patients with diabetes and in patients on long-term use of cortisone, such as those with severe arthritis or asthma.
6) Decrease in sensitivity to color
This change in color vision, is a subtle alteration in the quality of one's vision that may be overshadowed by more noticeable alterations in its clarity. Going through the cataractous process, the nucleus becomes more and more yellow. In becoming yellow, the affected lens absorbs wavelengths of first violet and the blue light, reducing those colors and making the environment appear yellowish.