Esotropia - Crossing of the Eyes

Baby Eyes
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Intermittent crossing of an infant’s eyes under about 4-5 months is normal. However, constant crossing of the eyes may be a concern. When an eye crosses inward it is termed esotropia. Esotropia is a type of strabismus. “Eso” means to turn inward toward the nose. An esotropia can occur in just one eye or alternate between both eyes. It is rare for both eyes to cross in at the same time. 

Causes of Esotropia

The cause of an esotropia depends on when it first occurs.

In adults, a sudden onset of esotropia can be a sign of a very serious condition. In infants and toddlers, esotropia is usually a sign of an abnormal development of the binocular system that develops in the brain. However, there are other causes. Below 4-5 months of age, intermittent crossing is usually normal and is just a sign of learning how to use the eyes together as a system. Some babies and ethnic groups may have pseudo-strabismus. This is a condition in which the bridge of the nose is not fully developed or flatter than normal. These kids have “epicentral folds" which make it appear that an eye is turning slightly. As the infant develops, this appearance usually goes away and their eyes appear normal.

Types of Esotropia

  • Congenital esotropiaCongenital esotropia is a type of esotropia that infants are born with. It usually caused by an abnormal wiring of the nerves or abnormal development in the motor areas of the brain. Congenital esotropia usually appears very early between 2-4 months and the size of the deviation or eye turn tends to be very large. Often, infants with congenital esotropia do not have a large amount of farsightedness or nearsightedness. It is instead caused by an abnormal development of the binocular system. The best way to correct congenital esotropia is with surgery. Surgery is not aimed at providing a way for the eyes to work together in a normal fashion but rather to correct the deviation to have a better cosmetic appearance. The eyes may still not work perfectly together, but the child will have a much improved cosmetic appearance.
  • Accommodative esotropia: Accommodative esotropia occurs around age 2. It is usually caused by a problem  with the two systems that control our eye muscles and the amount our eyes focus. The accommodative system (focusing system) allows our eyes to change power and focus so that objects remain clear no matter the distance. The binocular/alignment system controls how our eyes work together. When we look far away, our eyes are straight. When we look at something very close, our eyes converge or turn in and our eyes increase their focusing power. When we look back to a distance, we relax our focusing power and the eyes become straight again. Young children have huge amounts of focusing power. As a result, when a child has a very large amount of uncorrected farsightedness, the child attempts to make things clear by over-focusing. To achieve that, they have to focus a great deal to compensate for the uncorrected vision problem. When they focus this much, the binocular and focusing systems begin to get mixed signals. Usually, one eye will turn in. What is driving the focusing system also send signals for the eye muscles to converge the eyes inward. However, when they have to focus this much, abnormal signals go to the eye muscles and then one eye turns in and becomes crossed. Some children may not compensate and their eyes will not turn in, but they will have very poor vision because they are not over focusing. Their brain chooses to keep the muscles straight, but they see a very blurred image.

    Complications of Esotropia

    • Amblyopia: Amblyopia is a common developmental problem associated with esotropia. Amblyopia is a condition that occurs when one or both eyes never see a clear image. If the image is never seen clearly for a long enough period of time, permanent vision loss may develop. In esotropia, one eye may become turned in. When the eye is turned in, the brain typically suppresses or ignores the image the eye sees. Otherwise, the person with esotropia would see double constantly. If the brain suppresses that eye frequently, the normal development process of the human neurologic system gets disrupted and becomes wired incorrectly. The human neurologic system is very “plastic” up until age 7 and some researchers say until age 14. After age 14, the brain and nervous system become hard-wired and it is difficult to improve vision back to normal. Therefore, early treatment is critical. If aggressive treatment starts at an early age, improvement in vision is possible.
    • Lack of true depth perception: Humans and animals have depth perception because they have two eyes. The further apart an animal’s eyes are, the better depth perception is. When one eye is turned in or being suppressed, the person with esotropia only sees with one eye. Although there are environmental cues to judge depth, true depth perception is reduced. People with esotropia have a difficult time viewing three dimensional pictures and puzzles. This could potentially affect sports performance or future job performance.


      SOURCE: Clinical management of binocular vision. Third edition. Shieman, M., Wick, B., 2008 Lippincott Williams & Wilkins, ISBN-13 978-07817-7784-1

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