A cataract is a clouding of the eye's natural lens, which lies behind the iris and the pupil. 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 colors. Cataracts typically progress slowly to cause vision loss, and are potentially blinding if untreated. The condition usually affects both 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.
Some children develop cataracts, called congenital cataracts, before or just after birth; these are usually dealt with differently from cataracts in adults.
Types of cataracts
A subcapsular cataract occurs at the back of the lens. People with diabetes, high farsightedness or retinitis pigmentosa, or those taking high doses of steroid medications have a greater risk of developing a subcapsular cataract.
A nuclear cataract forms deep in the central zone (nucleus) of the lens. Nuclear cataracts usually are associated with aging.
A cortical cataract is characterized by white, wedge-like opacities that start in the periphery of the lens and work their way to the center in a spoke-like fashion. This type of cataract occurs in the lens cortex, which is the part of the lens that surrounds the central nucleus.
Signs and symptoms
Bilateral cataracts in an infant due to congenital rubella syndrome
As a cataract becomes more opaque, clear vision is compromised. A loss of visual acuity is noted. Contrast sensitivity is also lost, so 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 is demonstrated, an eye specialist consultation is recommended.
It may be advisable to seek medical opinion, particularly in high-risk groups such as diabetics, 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.
Human eye cross-sectional view, showing the position of the human lens, courtesy NIH National Eye Institute
Several factors can promote the formation of cataracts, including long-term exposure to ultraviolet light, exposure to ionizing radiation, secondary effects of diseases such as diabetes, hypertension and advanced age, or trauma (possibly much earlier); they are usually a result of denaturation of lens protein. Genetic factors are often a cause of congenital cataracts, and positive family history may also play a role in predisposing someone to cataracts at an earlier age, a phenomenon of "anticipation" in presenile cataracts. Cataracts may also be produced by eye injury or physical trauma. Atopic or allergic conditions are also known to quicken the progression of cataracts, especially in children. Cataracts can also be caused by iodine deficiency.
When symptoms begin to appear, you may be able to improve your vision for a while using new glasses, strong bifocals, magnification, appropriate lighting or other visual aids.
Think about surgery when your cataracts have progressed enough to seriously impair your vision and affect your daily life. Many people consider poor vision an inevitable fact of aging, but cataract surgery is a simple, relatively painless procedure to regain vision. Cataract surgery is very successful in restoring vision. In fact, it is the most frequently performed surgery in the United States, with more than 3 million Americans undergoing cataract surgery each year, according to PBA. Nine out of 10 people who have cataract surgery regain very good vision, somewhere between 20/20 and 20/40.
During surgery, the surgeon will remove your clouded lens and in most cases replace it with a clear, plastic intraocular lens (IOL).
New IOLs are being developed all the time to make the surgery less complicated for surgeons and the lenses more helpful to patients. Presbyopia-correcting IOLs potentially help you see at all distances, not just one. Another new type of IOL blocks both ultraviolet and blue light rays, which research indicates may damage the retina.