The tendency of both eyes to deviate only, but can be controlled by the brain to orthotropia, and keep both eyes monocular, this potential eye position deviation is called cryptopia. Absolute orthophoria is rare in life, and about 90% of people have cryptophoria, which is mostly mild horizontal cryptophoria, while vertical cryptophoria and rotational cryptophoria are rare. Occult strabismus can develop into apparent strabismus. Occult strabismus is associated with anomalous position of extraocular muscles, refractive error or neurogenic factors. If the fusion function of the brain loses control, the patient will develop a dominant strabismus. Once the symptoms of visual fatigue, such as headache, eye pain, blurred vision, unsustainable reading, and even diplopia and vertigo, appear, you should go to the hospital for specialized examination to prevent the development of cryptorchidism into dominant strabismus. Principles of treatment Asymptomatic cryptorchidism does not require treatment. If a patient with occluded strabismus shows symptoms of visual fatigue, refractive error should be corrected in time, exercise should be strengthened, mental tension and overexertion should be eliminated, and appropriate treatment should be given if necessary. Internal strabismus: Firstly, dilate the pupil and get proper glasses. It is not suitable for training, but surgical correction of eye position to reduce excessive collection and eliminate excessive adjustment, so that the symptoms of visual fatigue can be reduced or disappeared. External obliquity: training is the main focus, using convergence training to strengthen the strength of the internal rotation muscle of both eyes, young adults should not wear trigeminal lenses. For emmetropia of more than 10°(20Δ), surgery can be considered.