The most common sign that there may be a serious eye problem in a child is: No obvious sign at all!
Crossed eyes are easily noticed, and squinting due to uncorrected nearsightedness gives a distinctive appearance. But the most common cause of permanent vision loss in children may not be externally evident in any way!
Anisometropia refers to an asymmetry in refractive error, or glasses measurement. Basically, think of this as having two different shoe sizes or having one arm longer than the other.
It’s okay to have long arms or short arms, but if one is longer than the other, the developing brain may start to prefer one over the other. And then the left-handed child only learns how to write with one hand. Eventually, the ability to learn how to use the other hand will decline.
In the old days, the left hand was somehow considered inferior to the right. Nuns used to force young children to use their right hand - and this was successful, but only if started at a very young age. At a certain point, the brain development is relatively set, and can’t easily be changed anymore.
Similarly, if the eyes have an asymmetric focus (the anisometropia mentioned), a young child’s brain will tend to ignore the more out of focus image. Cells in the part of the brain responsible for vision in the nondominant eye will actually preferentially die off from disuse. Eventually, this disuse may result in permanent vision loss, called amblyopia.
Sometimes, the poorer seeing eye will then wander out of alignment, and this is an important sign for parents to observe. Quite commonly, however, the eyes remain straight, and therefore look cosmetically perfectly fine.
And, because the dominant, preferred eye continues to see well, the child may act completely normally, with excellent sight — as long as the “stronger” eye is uncovered. So, these children look and act perfect from a visual standpoint, and the problem is often missed for many years, often until it’s too late to remedy.
Anisometropic amblyopia is responsible for more total years of vision loss in the “lazy” eye than any other ocular disease (including cataracts and macular degeneration).
The way to detect this problem? Cover each eye separately and assess the vision on each eye in turn. Very young children won’t complain that one eye doesn’t see well — until you cover the better-seeing one.
Anisometropia can also be detected without the child’s participation, by finding an asymmetry in the reflection off the back of the eye. Ideally, this asymmetry is best measured by an experienced eye doctor with the pupils dilated, but photoscreening machines do a reasonable job and are very useful for mass screening.
So, be on the alert for kids who look and act normal — maybe they are, but maybe not! Finding and treating amblyopia is one of the most important and effective ways to save and develop a lifetime of vision.
Hope this helps! Please let me know if I can provide any further information.
Benjamin H. Ticho, MD
Ticho Eye Associates
Associate Professor of Ophthalmology
The University of Illinois Eye and Ear Infirmary