Amblyopia is poor vision caused by abnormal visual stimulation during early visual development. The abnormal visual stimulation disrupts neurodevelopment of visual centers in the brain. Abnormal stimulation can arise from a blurred retinal image or a manifest esotropia with strong fixation preference for one eye and cortical suppression of the nondominant eye. Children under 6 years of age are capable of strong cortical suppression which eliminates double vision.