
Cute kid, right
? Take another look. Notice anything not quite right? Although easily missed at a subtle glance, you should see that this boy’s eyes are pointing in different directions. (If you want to confirm, look for the two shiny spots of reflected light from each eye, and observe how they overly different locations). Mal-alignment of the eyes is called strabismus. It’s fairly common, seen in 2-4 children of every 100.
Aside from the aesthetic implications (kids with strabismus are sometimes presumed to be intellectually slow because of their appearance, despite that there is no association between strabismus and cognitive ability), strabismus is a dangerous condition in children. When adults develop strabismus, they report double vision; each eye is looking in a different direction, there are two unique visual inputs to the cortex, and the brain perceives two simultaneous visual representations of the visual field.
In contrast, children whose visual maturation is not yet complete (before age 7-9) are able to suppress the input from one, or both eyes. Chronic suppression over time leads to irreversible loss of visual circuits in the brain. The result is irreversible loss of vision in one eye. This is called Amblyopia. It can be caused by strabismus, as described, or other causes including congenital cataracts, retinoblastoma (an eye tumour), or refractive errors. Amblyopia is the greatest cause of monocular (one eye) blindness in people under 45 yrs old.
Importantly, Amblyopia is painless, and has no symptoms. The only way to detect Amblyopia, is by an objective test of visual acuity. You may notice a strabismus (which can result in Amblyopia) like the picture above, but often the cause of Amblyopia is just as unnoticeable as the result. Can you imagine discovering that your child has become permanently blind in one eye, and worse, that it could have been prevented? The important public-health message about Amblyopia, therefore, is that children should have their vision checked regularly by a health-care professional. This is equally true for the pre-verbal child.
In case you’re curious, treatment for Amblyopia involves reversing the cause when possible (e.g. fixing the strabismus with surgery), and then patching the good eye such that the brain is forced to receive input from the Amblyopic eye. This preserves, and strengthens, the brain circuitry from the affected eye.
(Yes, we’re on Ophthalmology this week! And I love it!!)