The brain is tasked with job of combining the two images seen in each eye. This process, called fusion allows for binocular depth perception. Sometimes, the image collected in each eye be different, making it impossible for the brain to fuse the images. The brain’s solution to the problem is to ignore one eye to allow for the visual universe to make sense. This is called suppression.
Why would the images be different?
When the images collected by each eye differs the brain may suppress that eye. This can occur when there is poor alignment of the eye as in a strabismus. This suppression is most likely to continue after surgical straightening of the eye.
Suppression may also occur when there is a difference in refractive error in each eye. This condition is called anisometropia.
Deprivation of visual stimulus caused by a congenital cataract may also cause suppression.
Is suppression harmful?
Suppression should always be investigated by an eye doctor when the cause is unknown. While the brain may briefly suppress at certain distances due to an issue in focusing, prolonged suppression can lead to a lack of development of the visual pathway in the suppressed eye and decreased acuity in that eye. This condition is called amblyopia more commonly known as “lazy eye”. The eye doctor may prescribe patching to improve vision in the suppressed eye. A therapist should not introduce patching for management of suppression under any circumstances. This should only be ordered by an eye doctor.
What can the vision aware therapist do to help?
Amblyopia can be related to motor delays which is where the role of therapeutic intervention is most helpful. Providing activities to do during patching is also helpful. Ocular motor activities and fine and gross motor tasks (providing the child can see well enough to participate) are all helpful in improving motor deficits and may help improve acuity in the suppressed eye quicker. Efforts to break suppression and make a person binocular should only be undertaken by a vision therapist under direct supervision of an optometrist. This would be considered beyond the scope of practice for OT and PTs.