Strabismus and lazy eye: how the two connect

Strabismus and lazy eye are often mixed up by families. They are not the same thing, but they are tightly linked: one is among the most common causes of the other.

This article covers where the two conditions meet, why a turn is not always visible, and what surgery does and does not solve.

Strabismus is the two eyes being unable to point at the same spot. While one eye fixes on the target the other may turn in, out, up or down. The turn can be constant, vary through the day, or show up only when the child is tired.

Some deviations are not visible to the naked eye at all; they only appear at an exam, when one eye is briefly covered and uncovered. So saying that an eye does not look turned is not proof that alignment is fine.

When the eyes point at different places, two conflicting scenes reach the brain. Because merging is impossible, the expected result is double vision.

A child's brain takes a practical route out of the discomfort: it suppresses the turning eye's image. That works in the short term and the child does not see double. But the suppressed eye's visual development falls behind, and amblyopia appears.

In adults the situation differs: having lost that flexibility, a strabismus that develops later usually produces double vision instead.

No. Some children alternate, using one eye for a while and then the other. Because no single eye is suppressed continuously, amblyopia may not develop.

The reverse is also true: the most common cause of lazy eye is not strabismus at all but a difference in prescription between the eyes, and in that case there is no visible turn. The absence of a visible sign does not mean the absence of a problem.

Strabismus surgery repositions the eye muscles to correct alignment. That can matter both for appearance and for the eyes' ability to work together.

But surgery does not treat the amblyopia itself. Even with alignment corrected, the brain's habit of suppressing that eye can persist, which is why vision training is planned separately, before or after the operation.

The order and the method differ for every child and are decided by the doctor. The next article takes on suppression, the common denominator behind all of these pictures.