What Causes Lazy Eye?

The most common causes of Lazy Eye (amblyopia) are constant Strabismus (constant turn of one eye in any direction, but an inward turn or crossed eyes is much more common), Anisometropia (differences in vision and/or prescription between the two eyes) which leads to anismetropic amblyopia or refractive amblyopia, and/or physical blockage of an eye due to cataract, trauma, lid droop (ptosis), blocked tear duct, etc. 

Most eye turns develop gradually. If you experience an eye turn that develops overnight or suddenly, especially with a discolored or pale pupil, you should seek immediate evaluation by an optometrist or ophthalmologist.

A very small percentage of children develop an eye turn very soon after birth (in the first 3-6 months). Usually, this type of turn is inward. The cause of this turn is a problem with the way the eye muscles are controlled by the brain. 

Most children develop a turned eye after the first year of life. The majority are due to hyperopia (far-sightedness, long-sightedness). Simply stated, the child has a focusing problem which causes a secondary eye turn. When your child focuses on an object, in order to see it clearly, there is also a stimulation of the muscles around the eye that pulls the eyes in. Eventually, the brain learns to adapt to this by leaving one eye in constantly and “turning it off” (suppression).  This eye turn is more likely to be noticed as the child becomes more involved in close work (ages 2-4 years). This is because close work requires greater focus effort to keep things clear. The turn may also be triggered by illness or fatigue, again due to the fact that there is an increased effort involved in keeping the world clear. There can also be an inherited risk (someone in the family also has an eye turn). This type of an eye turn is usually helped with eyeglass lenses. 

Some individuals have an excessive stimulation of the inner muscles that pull the eyes inwards when the eyes try to focus. This can occur even with relatively low degrees of hyperopia. Eventually, the brain learns to leave one eye in and “turns it off” to reduce the effort of coping with double vision.

Some children have a combination of the last two reasons. Either way, an eye turn is rarely due to solely an eye muscle problem.

References

BABO Informational pamphlet “Strabismus & Amblyopia”

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