Diplopia is a visual dysfunction in which one object is seen as two, and its occurrence is related to the failure of the same object to fall at the corresponding point in the retina of both eyes. The common causes include refractive error, keratoconus, cataract, lens subluxation, iris abnormalities, and vitreoretinal lesions. Bilateral diplopia includes physiological diplopia and pathological diplopia. Physiological diplopia is the basis for the formation of stereopsis, while pathological diplopia is mostly seen in non-common strabismus and can be clearly diagnosed by eye position, eye movement, traction test and imaging. Some pathological diplopia is often accompanied by symptoms and signs of the central nervous system, and should be consulted by neurology and other clinically relevant departments to avoid misdiagnosis. In addition, surgery, optical methods, and chemical denervation can be used.