A form of strabismus in which one or both eyes deviate outward away from the nose. It can be constant or periodic, occur in children and adults. The causes can be an imbalance of the oculomotor muscles, neurological disorders or hereditary factors. Symptoms include double vision, eye strain, and decreased stereoscopic perception; In children, if left untreated, amblyopia may develop. Treatment may include spectacle correction, visual therapy, and, if necessary, eye muscle surgery.