A Cataract is a clouding or opacity of the natural internal lens of
the eye which causes a visual impairment.
The natural lens is located behind the iris, or "colored part" of
the eye. The opacity may be a small dot or may involve the entire
The opacity in the lens causes the light entering the eye to be
scattered, causing images to appear hazy or blurred.
Clasification of Cataracts:
A. Late Onset (Senile)
Late Onset, or Senile, cataracts develop later in life and
accounts for 90% of all cataracts. They may sometimes have
contributing factors such as diabetes, ocular trauma, glaucoma or
the metabolic effects of aging.
1. Nuclear Cataract:
Nuclear Cataracts are the most common. These are frequently
related to aging. The appearance ranges from a faint haze in the
pupil to a deep burnished yellow, similar to a smoky fog. As a
result, the individual reports a "yellowing" of vision. Frequently,
there is a shift in glasses prescription to become less hyperopic
("far sighted") or more myopic ("near sighted"). For those that are
hyperopic, the vision improves and is said to have temporary
"second sight". As the cataract progresses, the shift continues
into myopia with resulting higher lens prescription. Individuals
who are developing nuclear cataracts, in the early stages,
frequently complain of lens prescriptions that do not seem quite
right. Another frequent complaint is "fluctuating vision", where
vision becomes less clear for brief periods. Occasionally, in the
early stages there will be "sharp pains" in the eye which last for
only a fraction of a second. These are the result of the eyes
musculature frustration trying to correct itself. Individuals often
complain of poor night vision and "blinding" headlights.
2. Posterior Subcapsular
Posterior Subcapsular cataracts appear in the center of the lens
of the eye. Most frequently, they occur on the posterior (back)
part of the lens. There is not any usual shift in lens prescription
such as is found in nuclear cataracts. Because they appear more in
the center of the lens, if the pupil is small, such as in bright
light, the vision is reduced. In contrast, in reduced light, such
as at night, the pupil is open, allowing light to go around the
cataract. As such, vision at night may be better. Or, the
individual may feel driving at night is easier than sunny days.
This type of cataract can also be related to a systemic disease or
prolonged steroid use.
3. Cortical Cataract:
The appearance of cortical cataracts show up as "spokes of a
wheel". The location of this lens opacity is in the cortex of the
lens. The opacity tends to be most pronounced in the periphery of
the pupil. This means that in bright daylight and normal room
lighting, the vision is not as affected as when the pupil is more
dilated at night.
4. Morgagnian (Mature)
The Mature Cataract is diffusely opaque or white. When the nucleus
of the lens has turned yellow, and has fallen by gravity to the
lower part of the lens, it is said to be a "Morgagnian Cataract".
Cataract surgery is hightly recommended when this type of cataract
develops due to the fact that damage will ultimately occur to the
inside of the eye. Secondary Glaucoma is a frequent
B. Congenital Cataracts:
In congenital cataracts the lens opacity is present at birth.
These type cataracts can be caused from genetic or maternal
reasons. There are many different morphological shapes. In infants,
congenital cataracts are usually bilateral and recognized by the
appearance of a white pupil, which is detected during a routine eye
examination in the baby's first six months of life. Maternal
reasons for the development of cataracts may include: syphilis,
rubella or secondary to amniocentesis. There are various types of
congenital cataracts. The specific treatment depends on the type
C. Infantile or Juvenile
Infantile or Juvenile Onset cataracts have a definite genetic
origin and tend to co-exist with other abnormalities such as inborn
errors of metabolism, identified chromosomal abnormalities, and
other eye conditions. Causes for these type of cataracts include:
diabetes, galactosemia, hyperlysinemia, homocystinuria, Down
Syndrome, Turners Syndrome, Muscular Dystrophy, Idiopathic
Hypoparathyroidism, Rieger's anomaly, aniridia and retinitis
D. Traumatic Cataract:
Traumatic cataracts can result from two major types of
Perforating Eye Injuries: If a sharp object penetrates the eye
(ex. wire) and penetrates the capsule of the lens in the eye, a
cataract will frequently develop. These usually will develop at a
Blunt Eye Injuries: If the eye is injured by a blunt compression
type injury, a cataract may develop up to several years after the
injury. Additionally, with this type of injury, the zonules
attaching to the lens capsule may be torn or injured, which may
impair the "near point" focusing ability for the individual.
E. Secondary Cataract:
A Secondary cataract, or Capsular Fibrosis, is directly related to
a specific disease, systemic disorder or chemical agent such as
prescription medications. The physical appearance and manifestation
of these different types of cataracts varies. For example, long
term use of prednisone (steroid) frequently will result in
cataracts. Many other medications have been found to cause
cataracts. The decision as to the use of these medications should
always be considered in light of this possiblity. Additionally,
cataracts can form secondarily to some type of systemic disease.
One disease that has frequently been shown to result in secondary
cataracts is diabetes.
Answers to your questions about
Scientists do not know the exact cause of cataract formation. They
do know that a chemical change takes place within the natural lens
of the eye causing it to become clouded. This clouding progresses
with age, and if left untreated, can cause severe visual
90% of cataracts are due to the normal aging process,
affecting people over the age of 50. Not all cataracts, however,
are due to age. Lens opacities can be present at birth, while
others develop by another cause. Some factors that have been found
to contribute to the formation of cataracts are: Age, Genetics,
Injury, Nutritional deficiencies, Ultra-violet (UV) radiation,
Chemotherapy, Steroid Therapy, Diabetes, or Renal Failure.
What are some symptoms of
Blurred, fuzzy or hazy vision
Seeing as though looking through a cobweb, or having a film over
Frequent changing of glasses prescriptions, or seeing better
Rings or halos around lights
Severe decrease in vision with glare or bright lights in the eye
"Blindness": Early cataracts may
impair sight, but fortunately the "blindness" is only temporary.
After the lens is removed and replaced with a new lens, sight is
restored. See cataract surgery for a more detailed explanation.
"Skin growing over the eye":
Cataracts are often confused with a pterygium, which is a
connective tissue growing over the cornea.
"Spreading of Cataracts": An
individual usually does have cataracts in both eyes, but this is
not due to a spreading from one eye to the other, as in an
TESTS TO EVALUATE A
Visual Acuity: When the vision
cannot be corrected to better than 20/50, surgery is recommended.
Biomicroscopy: This examination
enables the doctor to look at the cataract's shape and density in
order to evaluate the degree of expected vision loss.
Extended Ophthalmoscopy: Dilating
drops are placed in the eye so as to allow the doctor a direct view
of the back of the eye. This is important to assess the blood
circulation and any abnormalities that may contraindicate surgery.
See ophthalmoscopy for more detailed information.
Visual Fields: The visual fields
test measures the neurological sensitivity of the retinal nerves in
the back of the eye.
A-Scan: The A-Scan is a device to
measure the length of the eye by ultrasonography. The A-Scan's
computer is then able to calculate what the best IOL (intraocular
lens) power should be to achieve the best possible vision after
Glaucoma is an eye disease in which pressure increases in the eye
due to clogged or blocked passages. Fluid that normally drains
through these passages begins to build up, and the increased
pressure can damage the optic nerve. Open-angle glaucoma tends to
develop without warning--often painlessly and with no symptoms.
Because of this, it can cause damage and blindness more quickly
when untreated. Risk factors for developing glaucoma include people
over the age of 40; those who have a family history of glaucoma;
those who are very nearsighted; diabetics; and African-Americans.