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Disease: Cataracts Cataracts
Category: Eye diseases

Disease Definition:

The clouding of the normally clear lens of the eye is referred to as a cataract. Looking through a cloudy lens is similar to trying to see through a frosty or fogged-up window. It may become more difficult to see the expression on a friend's face, drive a car – especially at night – or read, because of clouded vision. Cataracts cause problems with glare and affect distance vision in general; however, they usually don't cause irritation or pain.


Most cataracts don’t disturb the eyesight early on and they develop slowly. However, the cataract eventually interferes with the vision as the clouding progresses. Eyeglasses and stronger lighting can help the patient deal with vision problems early on. However, he/she may need surgery if impaired vision jeopardizes his/her normal lifestyle. The good thing is that cataract removal is a safe, effective procedure in general.

Work Group:

Symptoms, Causes


A cataract usually causes no pain and develops slowly. In the beginning, the patient may be unaware of any vision loss, and the cloudiness may affect only a small part of the lens, which is a clear and elliptical structure near the front of each eye. But it clouds more of the lens and distorts the light passing through the lens over time as the cataract grows larger. Due to image distortion or overall blur, the cataract will eventually impair the person’s vision.


Here are the signs and symptoms of cataracts:


  • Frequent changes in eyeglass or contact lens prescription
  • Double vision in a single eye
  • Halos around lights
  • Fading or yellowing of colors
  • Increasing difficulty with vision at night
  • Clouded, blurred or dim vision
  • The need for brighter light for reading and other activities
  • Sensitivity to light and glare


Lamps, oncoming headlights or light from the sun may seem too bright when having a cataract. Driving may become uncomfortable and dangerous because of glare and halos around lights. One may blink more often to clear his/her vision or experience eyestrain.
Aching, irritation, redness, itching, pain in the eye or a discharge from the eye may be signs and symptoms of other eye disorders as they are not signs or symptoms of a cataract. And no change in the appearance of the eye is caused by cataracts.
Unless the cataract becomes completely white, a condition known as an overripe (hypermature) cataract, a cataract isn't dangerous to the physical health of the eye. Headache, pain and inflammation can be caused by this condition. If a hypermature cataract is associated with inflammation or pain, it requires removal.


In one or both of the eyes, a cataract can develop. However, cataracts tend to develop symmetrically in both eyes in most cases, except for those caused by injury or trauma. A cataract may or may not affect the entire lens.


Light passes through the cornea (the protective dome of clear tissue over the front of the eye) and the pupil (the hole in the center of the eye) to the lens, when the eyes work in a proper way. Just behind the iris (the colored part of the eye) and the pupil is where the lens is located. It is shaped thinner near the edges and thicker in the middle and is held in place by tiny ligaments, which are bands of tough tissue fiber. Producing clear, sharp images on the retina, which is the light-sensitive membrane on the back inside wall of the eyeball that functions like the film of a camera, the lens focuses light that passes through the cornea and pupil. Scattering the light and preventing a sharply defined image from reaching the retina, the lens becomes clouded as a cataract develops. Blurred vision is the result of this.



Three layers form the lens. The thin, clear membrane is the outer layer called capsule. It surrounds a soft, clear material called the cortex; the nucleus is the harder center of the lens. When thinking of the lens as a piece of fruit, the capsule is the skin, the cortex is the fleshy fruit and the nucleus is the pit.


The lenses in the eyes become thicker, less transparent and less flexible as a person ages. Water and protein fibers form most of the lens. In a precise manner that makes the lens clear and allows light to pass through without interference is how the protein fibers are arranged. The composition of the lens undergoes changes and the structure of the protein fibers breaks down with aging. Clouding small areas of the lens, some of the fibers begin to clump together. The clouding becomes denser and involves a greater part of the lens as the cataract continues to develop.


A cataract could form in any part of the lens.



There are three types of cataracts:


Just under the capsule of the lens, a subcapsular cataract starts as a small, opaque area. Near the back of the lens, right in the path of light on its way to the retina is where it usually forms. A subcapsular cataract usually reduces one's vision in bright light, causes glare or halos around lights at night and interferes with the reading vision.


A nuclear cataract occurs in the center of the lens. The patient may become more nearsighted or even experience a temporary improvement in his/her reading vision as the lens changes the way it focuses light in the early stages of this type. In fact, some people stop needing their glasses. The sad thing is that as the lens gradually turns more densely yellow and further clouds the person’s vision, and this so-called second sight disappears. The lens may even turn brown as the cataract progresses. It may be especially troublesome when seeing in dim light and driving at night. Difficulty distinguishing between shades of blue and purple can be caused by advanced discoloration.


A cortical cataract begins as whitish, wedge-shaped opacities or streaks on the outer edge of the lens cortex. The streaks extend to the center and interfere with light passing through the center of the lens as it slowly progresses. For people with this type of cataract, problems with glare are common.


The reason why a lens changes with age is not really known. Damage caused by unstable molecules known as free radicals is one possibility. Two sources of free radicals are smoking and exposure to ultraviolet (UV) light. The changes in protein fibers may be caused by general wear and tear on the lens over the years as well.



Cataracts are not only caused by age-related changes in the lens. Some people develop cataracts during childhood or are born with them in a case that is called congenital cataracts. The mother having contracted German measles (rubella) during pregnancy may be the cause of such cataracts. Metabolic disorders may be the cause of this case as well. If congenital cataracts affect vision, they're usually removed soon after detection; however, they don't always affect vision.


Just because age is the greatest risk factor for cataracts, everyone is at risk of developing the condition.


The risk of cataracts may increase due to the following factors:


  • Prolonged use of corticosteroids
  • Diabetes
  • Previous eye injury or inflammation
  • Family history of cataracts
  • Exposure to ionizing radiation
  • Previous eye surgery





Surgery to remove the clouded lens is the only effective treatment for cataracts; this surgery includes replacing the lens with a clear lens implant. Vision can be corrected with eyeglasses or contact lenses in the cases when cataracts are removed without reinserting implant lenses. In about 95% of all cases, cataract surgery is successful.


People were advised to wait until their vision had deteriorated to about 20/200, which would seriously impact their vision, in the past. However, nowadays, surgery is recommended in general when cataracts begin to affect one's quality of life or interfere with his/her ability to perform normal daily activities because the risks from cataract surgery are much lower than before and surgical techniques have improved.


Surgery is done on only one eye at a time. Usually with local anesthesia, it is generally done on an outpatient basis. The patient can often resume his/her normal daily activities beginning the night of the surgery, as recovery is fast. The day after surgery, after the postoperative checkup, the patient may be able to start driving again.


Optical devices, exercises, dietary supplements or medications can't cure cataracts. A good understanding of the condition and a willingness to adjust one's lifestyle can help in the early stages of a cataract when symptoms are mild. The effects of having a cataract may be dealt with by some self-care approaches, such as improving the lighting in one's home or using a magnifying glass to read.  


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