What causes crossed eyes?

Strabismus, also known as crossed eyes, has various causes, primarily including genetics, anatomical structural abnormalities, underdevelopment or damage of the nervous system, and visual environmental factors. Genetic factors play a significant role in the development of strabismus; individuals with a family history of strabismus have a relatively higher risk of developing the condition. In addition, abnormalities in ocular anatomy—such as poor development of the eye muscles, abnormally long or short axial length of the eye, and refractive errors—may also lead to strabismus. Underdevelopment or injury of the nervous system, such as brain injury or cerebral palsy, along with poor visual habits and environmental factors—including prolonged near-work and incorrect eye-use posture—can also trigger strabismus. Furthermore, eye diseases such as cataracts and keratitis may cause strabismus as well.