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A Cataract is a clouding of opacity of the natural internal lens of the eye which causes a visual imparment. 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 lens.
The opacity in the lens causes the light entering the eye to be scattered, causing images to appear hazy or blurred.
CLASSIFICATIONS OF CATARACTS
A. Late Onset (Senile) Cataracts:
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 site". 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 lasts 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 Cataract:
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 the 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 on 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) Cataract:
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 highly 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 complication.
B. Congenital Cataracts:
In congenital cataracts the lens opacity is present at birth. These types of 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 fo cataracts may include: syphilis, rubella, or secondary to amniocentesis. There are various types of congenital cataracts. The specific treatment depends on the type and severity.
C. Infantile or Juvenile Cataracts:
Infantile or Juvenile Onset cataracts have a definite genetic origin and tend to co-exist with other abnormalities such as inborn errors of metabolism, indentified chomosomal abnormalities, and other eye conditions. Causes for these types of cataracts include: diabeties, galactosemia, hyperlysinemia, homocystinuria, Down Syndrome, Turners Syndrome, Muscular Dystrophy, Idiopathic Hypoparathyroidism, Rieger's anomaly, aniridia and retinitis pigmentosa.
D. Traumatic Cataracts:
Traumatic cataracts can result from two major types of injuries:
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 fast rate.
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 impare the "near point" focusing ability for the individual.
E. Secondary Cataracts:
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 diabeties.
ANSWERS TO YOUR QUESTIONS ABOUT CATARACTS:
Why do cataracts form?
Scientists do not know the exact cause of cataract formation. However, 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 servere visual impairment.
Who gets cataracts?
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, Diabeties, or Renal Failure.
What are some symptoms of cataracts?
Misconceptions about cataracts:
"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 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 infectious process.
TESTS TO EVALUATE A CATARACT:
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 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 field test measures the neurological sensitivity of the retinal nerves in the back of the eyes.
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 surgery.
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