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.
Types of Cataracts
Age-related cataracts. As the name suggests, this type of cataract develops as a result of
Congenital cataracts. Babies are sometimes born with cataracts as a result of an
infection, injury, or poor development before they were born, or they may develop during
Secondary cataracts. These develop as a result of other medical conditions, like
diabetes, or exposure to toxic substances, certain drugs (such as corticosteroids or
diuretics), ultraviolet light, or radiation.
Traumatic cataracts. These form after injury to the eye.
Cataracts usually form slowly and cause few symptoms until they noticeable block light.
When symptoms are present, they can include:
Clouded, blurred or dim vision
Increasing difficulty with vision at night
Sensitivity to light and glare
Seeing “halos” around lights
Double vision in a single eye
Fading or yellowing of colors
At first, the cloudiness in your vision caused by a cataract may affect only a small part of
the eye’s lens and one may be unaware of any vision loss. As the cataract grows larger, it
clouds more of the lens and distorts the light passing through the lens.
Most cataracts develop when aging or injury changes the tissue that makes up the eye’s
lenses. Some cataracts are caused by inherited genetic disorders that cause other health
problems and increase the risk of cataracts. Cataracts occur when there is a buildup of
protein in the lens that make it cloudy.
The eye functions much like a camera. Light rays enter the eye, passing through the
cornea, the aqueous humor, which is the transparent fluid in the front of the eye and then
the pupil and into the lens. The lens bends the light rays to focus objects onto the retina
lining the back of the eye. From there, the image passes through the retinal cells, into the
optic nerve, and finally to the back of the brain which process the images. A cataract
scatters the light as it passes through the lens, preventing a sharply defined image from
reaching the retina. Vision becomes blurred.
As you age, the lenses in your eyes become less flexible, less transparent and thicker.
Aging-related changes to the lens cause tissues to break down and to clump together,
clouding small areas of the lens, as the cataract continues to develop, the clouding
becomes denser and covers a greater part of the lens.
Most doctors consider waiting until a certain point in the development of the cataract,
although times vary between doctors.
When the cataract is sufficiently developed to be removed, surgery is performed. There
are two types of eye surgery that can be used to remove cataracts: extra-capsular cataract
extraction, or ECCE and intra-capsular 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 are sometimes used to break up the lens before
extraction. 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.
Cataract in the Adult eye. American Academy of Opthalmology. Retrieved July 2, 2010,
Facts about cataract. National Eye Institute. (n.d.) Retrieved July 2, 2010 from
Cataract surgery. EyeCare America. Accessed July 2, 2010 from
Cataract surgery. American Optometric Association. 2007,August 8) Retrieved July 2,
2010, from http://www.aoa.org/x9954.xml.
Cataracts (n.d.) Retrieved July 2, 2010, from
Developed by Kathleen Sanders