Amblyopia is a decrease in vision in one or both eyes in which there are no structural defects. It is a diagnosis of exclusion, meaning that when a decrease in vision is detected, other causes must be ruled out. Once no other causeis found, amblyopia is the diagnosis.

Lazy eye is a common non-medical term used to describe amblyopia because theeye with poorer vision doesn't seem to be doing its job of seeing. Amblyopiais the most common cause of impaired vision in children, affecting nearly 3 out of every 100 people or 2-4% of the population.

Vision is a combination of the clarity of the images of the eyes (visual acuity) and the processing of those images by the brain. If the images produced by the two eyes are substantially different, the brain suppresses the blurrierimage. This suppression can lead to amblyopia. During the first few years oflife, preferring one eye over the other may lead to poor visual developmentin the blurrier eye.

There are several causes of amblyopia. Strabismus, or crossed eyes, is the most common cause of functional amblyopia. The brain receives two different images and this causes confusion. Images from the misaligned or crossed eye areturned off to avoid double vision. Anisometropia is another type of functional amblyopia. In this case, the two eyes do not have the same ability to focuson an image. For example, one eye may be more nearsighted than the other eye. Clouding of the lens of the eye, or cataract, will cause the image to be blurrier than the other eye. Ptosis is the drooping of the upper eyelid. If light cannot enter the eye because of the drooping lid, the eye is essentially not being used. Nutritional deficiencies or chemical toxicity may result in amblyopia. Alcohol, tobacco, or a deficiency in the B vitamins may result in toxic amblyopia. Amblyopia can also run in families.

Because children with outwardly normal eyes may have amblyopia, it is important to have regular vision screenings. While there is some controversy regarding the age children should have their first vision examination, their eyes can, in actuality, be examined at any age, even at one day of life.

There is a critical period in vision development, and amblyopia may not be treatable after age eight or nine. The earlier amblyopia is found, the better the outcome. Most physicians test vision as part of a child's medical examination. If there is any sign of an eye problem, they may refer a child to an eyespecialist.

The primary treatment for amblyopia is occlusion therapy, or eye patching. Itis important to alternate patching the good eye and the amblyopic eye. The treatment plan should be discussed with the doctor to fully understand how long the patch will be on. Eye exercises may be prescribed to force the amblyopic eye to focus and work. This is called vision therapy or vision training. Even after vision has been restored in the weak eye, part-time patching may berequired over a period of years to maintain the improvement.

While patching is necessary to get the amblyopic eye to work, it is just as important to correct the reason for the amblyopia. Glasses may also be worn. Surgery or vision training may be necessary in the case of strabismus. Betternutrition is indicated in some toxic amblyopias. Occasionally, amblyopia is treated by blurring the vision in the good eye with eye drops or lenses.

The younger the person, the better the chance for improvement with occlusionand vision therapy. However, treatment may be successful in older children--even adults. Success also depends upon how severe the amblyopia is, the specific type of amblyopia, and patient compliance. It is important to diagnose andtreat amblyopia early because significant vision loss can occur if left untreated.

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