What is a cataract?
A cataract is a clouding or opaque area over the lens of the eye – an area that is normally transparent. As this thickening occurs, it prevents light rays from passing through the lens and focusing on the retina – the light sensitive tissue lining located in the back of the eye. This clouding is caused when some of the protein which makes up the lens begins to clump together and interferes with vision.
In its early stages, a cataract may not cause a problem. The cloudiness may affect only a small part of the lens. However, the cataract may grow larger over time and affect more of the lens, making it harder to see. As less light reaches the retina, it becomes increasingly harder to see and vision may become dull and blurry. While cataracts cannot spread from one eye to another, many persons develop cataracts in both eyes.
What causes cataracts?
Although scientists do not know for sure what causes cataracts, they suspect there could be several possible causes including:
Excessive exposure to sunlight
Certain major tranquilizers
For several of the potential causes listed (such as steroids, diuretics, and/or major tranquilizers), additional research is needed to differentiate the effect of the disease from the effect of the drugs themselves.
What are the symptoms of cataracts?
The following are the most common symptoms of cataracts. However, each individual may experience symptoms differently. Symptoms may include:
Cloudy or blurry vision
Lights appear too bright and/or present a glare or a surrounding halo
Poor night vision
Colors seem faded
Increased nearsightedness, increasing the need to change eyeglass prescriptions
Distortion of vision in either eye
Often in the disease's early stages, you may not notice any changes in your vision. Since cataracts tend to grow slowly, your vision will worsen gradually. Certain cataracts can also cause a temporary improvement in close-up vision, but this is likely to worsen as the cataract grows. The symptoms of cataracts may resemble other eye conditions. Consult a physician for diagnosis.
What are the different types of cataracts?
According to the National Eye Institute, part of the National Institutes of Health, cataract types are subdivided accordingly:
Age-related cataractsThe majority of cataracts are related to aging.
Congenital cataractsSome babies are born with cataracts or develop them in childhood, often in both eyes. Some congenital cataracts do not affect vision, but others do and need to be removed.
Secondary cataractsSecondary cataracts develop primarily as a result of another disease occurrence in the body (for instance, diabetes). Secondary cataract development has also been linked to steroid use.
Traumatic cataractsEye(s) that have sustained an injury may develop a traumatic cataract either immediately following the incident, or several years later.
Other sources, including the American Academy of Ophthalmology, describe the different types of cataracts according to the cataract location on the eye lens, including:
Nuclear cataractThis is the most common type of cataract, and the most common type associated with aging. Nuclear cataracts develop in the center of the lens and can induce myopia, or nearsightedness – a temporary improvement in reading vision that is sometimes referred to as "second sight." Unfortunately, "second sight" disappears as the cataract grows.
Cortical cataractThis type of cataract initially develops as wedge-shaped spokes in the cortex of the lens, with the spokes extending from the outside of the lens to the center. When these spokes reach the center of the lens they interfere with the transmission of light and cause glare and loss of contrast. This type of cataract is frequently developed in persons with diabetes, and while it usually develops slowly, it may impair both distance and near vision so significantly that surgery is often suggested at an early stage.
A subcapsular cataract usually starts as a small opacity under the capsule, at the back of the lens. This type of cataract develops slowly and significant symptoms may not occur until the cataract is well developed. A subcapsular cataract is often found in persons with diabetes, myopia, retinitis pigmentosa, and in those taking steroids.