Causes

Some of the major causes of amblyopia are as follows:

• Strabismus. A misalignment of the eyes (strabismus) is the most common cause of functional amblyopia. The two eyes are looking in two different directions at the same time. The brain is sent two different images and this causes confusion. Images from the misaligned or "crossed" eye are turned off to avoid double vision.

• Anisometropia. This is another type of functional amblyopia. In this case, there is a difference of refractive states between the two eyes (in other words, a difference of prescriptions between the two eyes). For example, one eye may be more nearsighted than the other eye, or one eye may be farsighted and the other eye nearsighted. Because the brain cannot fuse the two dissimilar images, the brain will suppress the blurrier image, causing the eye to become amblyopic.

• Cataract. Clouding of the lens of the eye will cause the image to be blurrier than the other eye. The brain "prefers" the clearer image. The eye with the cataract may become amblyopic.

• Ptosis. This 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. This can lead to amblyopia.

• Nutrition. A type of organic amblyopia in which nutritional deficiencies or chemical toxicity may result in amblyopia. Alcohol, tobacco, or a deficiency in the B vitamins may result in toxic amblyopia.

• Heredity. Amblyopia can run in families.

Symptoms

Amblyopia should be suspected in a child if any of the following are seen:

• Eyes that turn in or out
• Eyes that do not appear to work together
• Inability to judge depth correctly
• Crying or complaining when one eye is covered
• Squinting or tilting the head up, down, or sideways to look at something
• Cloudiness in the black center of the eye

Screening and Diagnosis

Amblyopia is usually easily diagnosed with a complete examination of the eyes. Special tests are usually not required.

Treatment

Treatment has three primary goals: foremost, to obtain the best possible vision in each eye; second, to gain the best possible alignment of each eye alone and as a pair; and, finally, to provide the best possible opportunity for binocular vision.

• Atropine

A drop of a drug called atropine is placed in the stronger eye once a day to temporarily blur the vision so that the child will prefer to use the eye with amblyopia. Treatment with atropine also stimulates vision in the weaker eye and helps the part of the brain that manages vision develop more completely.

• Patching

An opaque, adhesive patch is worn over the stronger eye for weeks to months. This therapy forces the child to use the eye with amblyopia. Patching stimulates vision in the weaker eye and helps the part of the brain that manages vision develop more completely. To be effective, patching must usually be done for a minimum of six hours each day.

Prognosis

When treatment starts before age 5, near complete recovery of normal vision is usually possible. This becomes progressively less likely as children become older. Only partial recovery can be expected after age 10.

Complications

• Complex problems with muscle alignment may require several surgeries, which can have complications.

• Late treatment may result in permanent vision loss in the affected eye.