Amblyopia and strabismus (lazy and turned eyes)
Strabismus (eye turn) and Amblyopia (lazy eye) are the most common disorders of binocular vision. When the brain has difficulty using the 2 eyes together well, strabismus or amblyopia can develop. In some cases this can be due to a problem with an eye muscle, but more often it is due to a neurological difficulty where the brain cannot fuse together the two images together from each eye. One eye usually becomes much weaker than the other, failing to achieve normal eyesight even with prescription glasses or contact lenses, as the brain finds it easier to just use one eye than two together.
Amblyopia begins during infancy and early childhood. In most cases, only one eye is affected. But in some cases, reduced visual acuity can occur in both eyes.
If lazy eye is detected early in life and promptly treated, the prognosis for better vision development is easier. If left untreated, lazy eye can cause severe visual disability in the affected eye, including legal blindness. Up until recently it was thought that an eye turn or lazy eye could only be treated up until the age of about 8 years of age (the critical period). This has shown to be not the case, with many older children, teenagers and adults, being able to improve their vision and use of their two eyes together.
Amblyopia Signs and Symptoms.
Because amblyopia typically is a problem of very young children, symptoms of the condition can be difficult to detect. A common cause of amblyopia is strabismus (turned eye).So if you notice your baby or young child has crossed eyes or some other apparent eye misalignment, schedule an appointment for a children’s eye exam immediately.
Another clue that your child may have amblyopia is if he or she cries, fusses or becomes agitated when you cover one eye. This may suggest that the eye you have covered is the “good” eye, and that the uncovered eye is amblyopic, causing blurred vision.
What Causes Amblyopia?
Strabismus is the most common cause of amblyopia. To avoid double vision caused by poorly aligned eyes, the brain ignores the visual input from the misaligned eye, leading to amblyopia in that eye (the “lazy eye”). This type of amblyopia is called strabismic amblyopia.
Sometimes, amblyopia is caused by unequal focusing between the two eyes, despite perfect eye alignment. For example, one eye may have significant uncorrected long sightedness or short sightedness, while the other eye does not. Or one eye may have significant astigmatism and the other eye does not.
In such cases, the brain relies on the eye that has less uncorrected refractive error and ignores the blurred vision from the other eye, causing amblyopia in that eye from disuse.
Ultimately amblyopia and strabismus are problems of the brain’s visual system using the 2 eyes together well. The brain uses the main input of vision through the dominant eye, with weaker input from the other eye.
In some cases of amblyopia, normal vision can be achieved simply by fully correcting the focussing errors in both eyes with glasses or contact lenses. Often, however, vision therapy is required to retrain the brain to use the 2 eyes together. It may also involve some part time patching of the “good” eye to help the brain to pay attention to the visual input from the amblyopic eye and enable normal vision development to occur in that eye.