What is strabismus and why is it caused?

Strabismus is a visual problem in which there is a misalignment of the eyes. There are different types of strabismus and their classification depends on the direction of the eyes.

The most common types are:

  1. Endotropias: eyes deviated towards the center. Types of endotropias include infantile endotropia, accommodative endotropia and a sixth cranial nerve palsy.
  2. Exotropias: eyes deviated outward.
  3. Hypotropias and hypertropias: downward and upward eyes, respectively. Hypertropia is when the eye is abnormally positioned higher than the normal eye. Hypotropia, however, occurs when the abnormal eye is in a lower position than the normal eye. Both are types of vertical strabismus.

Its causes are diverse although the three cranial nerves (III, IV and VI) are responsible for eye movements, but they can become weak and cause strabismus. There are special patterns of strabismus that are given names such as Brown’s syndrome and Duane’s syndrome.

What causes strabismus?

Most strabismus results from an abnormality of neuromuscular control of eye movements. Strabismus can also be found in association with extraocular muscle problems, but is less common.

Strabismus is related to poor vision, especially in children, as the deviation of the eyes can cause amblyopia. When the eyes are oriented in different directions, the brain receives two visual images. The brain ignores the image coming from the misaligned eye to avoid double vision resulting in abnormal vision development.

In adults, stroke is the leading cause of strabismus. Trauma, neurological problems and Graves’ disease are other causes of adult strabismus.

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Trauma can damage the brain, nerves or cause direct or secondary damage to the extraocular muscles.

How can it be treated?

The goal of strabismus treatment is to improve the alignment of the eyes to allow them to work again. Treatment involves the use of glasses, muscle exercises, prisms or muscle surgery.

Some of the problems associated with strabismus are amblyopia, ptosis and cataracts and are usually treated before surgery.