Double vision is the simultaneous perception of two images, usually overlapping of a single scene, or non-matching images. Technical term for double vision is called diplopia. If someone is suffering from double vision, he maybe has visual impairment or has drunk too much alcohol. And diplopia may disappear when one eye is covered.
There are mainly two reasons of being double vision or diplopia. Misalignment of the two eyes is the most common cause of double vision. This means the eyes have functional problems that need medical evaluation of the optical system or treatment. This type of double vision is called binocular diplopia. And this type of double vision can be caused by an accident or head trauma. The other cause of double vision is a structural defect in the patient’s vision system. For example, cataract might be the reason of being diplopia. In this case, double vision may appear in only one eye, so this type of eye disease is called monocular diplopia.
Double vision can be a signal of many visual diseases such as strabismus, convergence insufficiency and the loss of vision, or it may be a symptom of head injuries. So when double vision appears, it is necessary for you to visit your eye doctor. Your eye doctor will get you vision therapy, or carry out an eye muscle surgery or orthoptics if needed.