What Causes Lazy Eye?

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  • Written By: Marlene de Wilde
  • Edited By: O. Wallace
  • Last Modified Date: 27 October 2019
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Lazy eye, or amblyopia, is caused by the improper stimulation of the nerve connections between the eye and the brain during infancy and early childhood. It is a neurological process where the brain compensates for, inhibits or suppresses poor sensory information such as blurry vision. The brain favors the strong signals being sent by the healthy eye to such an extent that it eventually ignores the signals coming from the affected eye, possibly resulting in permanent loss of vision. Lazy eye usually affects only one eye, but it can affect both.

There are a number of eye disorders which can lead to lazy eye. The most common cause is strabismic amblyopia which is sometimes evident by the strabismus, or squint, in one eye but can also be virtually undetectable unless by an expert. Anisometropic amblyopia is another cause of lazy eye where there is a refractive error. Variation in the direction of light means that the eyes differ in their ability to focus. Ametric amblyopia also concerns a refractive error, but this time it occurs in both eyes. Finally, there is stimulus deprivation amblyopia which is the rarest cause of lazy eye but often the most severe.


Strabismus is the result of irregularities in the muscles responsible for positioning the eyes. As a result, the eyes are unable to coordinate with each other when following a stimulus and one eye either crosses in or turns out. This is not to say that lazy eye and strabismus are the same thing. Constant strabismus causes lazy eye when long term compensation or suppression of poor sensory signals results in a permanent decrease in vision in the affected eye or eyes.

Anisometropic amblyopia is due to short-sightedness, long-sightedness or astigmatism. Refractive errors result in a difference in the direction of light when it passes through the air and into the eye. When one eye is affected, the brain will eventually ignore that eye and favor the good one. As a result, the affected eye becomes lazy. When the condition is ametropic, the refractive errors are large and affect both eyes. As a result, vision is constantly blurred.

Stimulus deprivation amblyopia is often the most severe cause of lazy eye for which the only treatment is often through surgery. This is when the eyes are prevented from seeing due to a tumor, congenital cataracts or an eye disease such as a corneal ulcer. There may also have been some injury caused to the eye or damage through surgery.

The other causes of lazy eye can often be corrected using glasses, patches and eye drops if the problem is caught early enough. The aim of these procedures is to make the affected eye work harder while inhibiting the good eye. This means that the brain is forced to acknowledge the affected eye and thus the nerve pathways are strengthened.



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