In monocular diplopia, the diplopia does not disappear after covering one eye, and the diplopia still occurs after covering one eye, the pathogenesis is mostly ophthalmologic; in binocular diplopia, the object cannot fall on the central recess of the retina of the skewed eye after one eye is skewed, resulting in the same object not being imaged on the corresponding point of the retina of both eyes, the diplopia can disappear after covering one eye.