Double vision, also called diplopia, is a symptom whereby a patient sees two images of a single object. It can be either monocular diplopia where the problem affects one eye only, or binocular diplopia where the problem comes from misalignment of both eyes.
In monocular diplopia, the double vision affects one eye and is present even when the other unaffected eye is covered. Monocular diplopia can be caused by uncorrected refractive errors, corneal disorders, cataracts and retinal disorders.
Binocular diplopia arises as a result of misalignment of the two eyes. The double image is only present when both eyes are open and disappears when either eye is covered.
Based on the kind of misalignment the double vision can be horizontal, vertical or oblique. Binocular double vision can be caused by disorders affecting the nerves, eye muscles, nerve-muscle junction or socket bones of the eye.
If experiencing double vision, it is important to check if the double vision is monocular or binocular by covering each eye in turn. This will help your doctor distinguish the likely cause of the double vision.