In medical terms, crossed eyes refer to internal strabismus, which is a type of strabismus with the highest incidence in children. Severe internal strabismus can be detected by direct observation. For non-obvious strabismus, parents can shine a flashlight on the bridge of the baby’s nose and encourage the baby to look at the flashlight. If the reflective spot of one eye appears in the center of the pupil toward the outer corner of the eye, it indicates the presence of crossed eyes. If the baby is within 6 months of age, no intervention is usually given; if the baby is still cross-eyed after 6 months, it is recommended to go to the hospital to confirm the diagnosis and treatment. The specific examination methods are as follows: 1. Basic examination: ask whether amblyopia treatment has been done, whether there is a family history, as well as visual acuity examination, refractive examination, and routine external eye, eye and fundus examination; 2. Specialist examination: include two parts: oculomotor function examination and binocular visual function examination. If the diagnosis of internal strabismus is confirmed, treatment and correction will be required according to the specific type. The more common types of acquired internal strabismus are moderate internal strabismus and non-moderate internal strabismus, and their treatment methods are mainly surgical and non-surgical treatments. Most congenital strabismus requires surgery, and non-modulated strabismus with a large slope usually requires surgery. Surgery can adjust the strength of the external eye muscles and the position of the attachment points to normalize the eye position. If the strabismus is moderate, it can be corrected with appropriate distance glasses or bifocals, and surgery is usually not necessary.