Diplopia is divided into monocular diplopia and binocular diplopia. The main cause of monocular diplopia is the presence of ophthalmic diseases, such as cataract, lens hemianopia, iris root dissection, etc. Binocular diplopia refers to diplopia caused by the inability of the visual center of the brain to fuse the same object image of both eyes into one, i.e., strabismus and central diseases are the main causes of binocular diplopia.