The eye has six muscles which control eye movement and are attached to the outside of each eye. The muscles work in conjunction thus if one muscle moves in the eye to the right, a different one muscle will move the eye to the left. The other four muscles move it up or down and at an angle.
To focus both eyes on an object, all of the muscles in each eye must be balanced, coordinated and working together. The brain controls these muscles.
With normal vision, both eyes aim at the same spot. The brain then combines the two pictures into a single, three-dimensional image. This three-dimensional image gives us depth perception.
When one eye is out of alignment, two different pictures are sent to the brain. Thus when a young child experiences this their brain learns to ignore the image of the misaligned eye and sees only the image from the straight eye. The child then loses depth perception.
Adults who develop strabismus often have double vision because their brains have already learned to receive images from both eyes and cannot ignore the image from the deviating eye.
Strabismus is especially common among children with brain disorders, such as:
- Cerebral palsy
- Down syndrome
- Brain tumors
Strabismus may cause reduced vision, or amblyopia, in the misaligned eye.
The brain will pay attention to the image of the straight eye and ignore the image of the crossed eye. If the same eye is consistently ignored during early childhood, this misaligned eye may fail to develop good vision, or may even lose vision.
Amblyopia can be treated by patching or blurring the stronger eye to strengthen and improve vision in the weaker eye. If amblyopia is detected in the first eight years of life, treatment is usually more successful. If treatment is delayed, amblyopia may become permanent. As a rule, the earlier amblyopia is treated, the better the result for vision.