One of the most famous of all eye conditions, amblyopia – better known colloquially as lazy eye – is a vision development disorder (and not a disease or illness). It is fairly common, affecting approximately 3% of Canadians, and generally develops during childhood.
In Canada, it is very rare to see amblyopia actually damage someone’s vision. Usually a doctor or optometrist would have spotted and addressed it appropriately before it causes vision loss. However, if left untreated, amblyopia can have devastating consequences. It can lead to serious vision impairment in the affected eye, and can even result in complete vision loss.
Amblyopia almost always begins developing in childhood- usually during infancy. It is one of the things that we look for during a pediatric eye exam.
Amblyopia is usually the result of one eye being unable to properly see, causing the brain to begin to favour the stronger eye. There are many reasons this may happen, such as a particularly potent refractive error impairing vision (such as severe myopia), though the usual cause is strabismus.
Even with corrective lenses, people with strabismic amblyopia will be unable to properly see in the affected eye. This is due to improper eye alignment (strabismus) interfering with the eye’s visual development.
Because the brain is unable to get a clear picture from the affected eye, it begins to trust the stronger eye exclusively. The eye with amblyopia becomes disused, and as it becomes weaker, its ability to see degrades even further.
As mentioned previously, refractive errors can also cause amblyopia to form. Severe untreated myopia, hyperopia, and astigmatism in one eye will cause the brain to react similarly to how it does with strabismus: by “turning off” the affected eye.
In most cases, refractive errors can be corrected via corrective lenses (eyeglasses or contacts).
Amblyopia can also be caused by vision conditions that prevent the eye from properly seeing. In kids, we see this most commonly as congenital cataracts. While the method is different, the end result is the same: the brain favours the stronger eye due to the poor vision quality in the affected one.
Treatment is most effective in young children, as the eyes and visual system develop rapidly during the first decade of our lives. In most cases, with proper treatment, amblyopia does not cause any long-term degradation of vision quality.
Vision therapy is a common tool for treating amblyopia. The process itself is a combination of several different exercises and tests; the processes that benefit amblyopia the most are part of a technique called deprivation therapy. This used to be done primarily through eye patching, though modern techniques usually involve specialized eye drops.
In deprivation therapy, atropine eye drops – eye drops that cause your eye to dilate and blur vision – are used to deprive the brain the sensory information from the stronger eye. This forces the brain to rely on both eyes for sensory input. Over time, the brain relearns how to properly use the amblyopic eye, restoring functionality to the eye.
If done early enough – generally before the child is 10 – vision therapy can restore eye function and visual acuity.