Diplopia

Diplopia, commonly known as double vision, is the perception of two images from a single object. The images may be horizontal, vertical, or diagonal.

Binocular diplopia
Double vision can occur when the two eyes are not correctly aligned while aiming at an object, such as in esotropia and exotropia - these result in uncrossed diplopia and crossed diplopia, respectively (i.e. "crossed eyes", in esotropia, result in uncrossed diplopia). When the eyes are misaligned and aimed at different targets, two non-matching images are sent to the viewer's brain. When the viewer's brain accepts and uses two non-matching images simultaneously, double vision results.

Double vision is dangerous to survival, therefore, the brain naturally guards against its occurrence. In an attempt to avoid double vision, the brain can ignore one eye (suppression). Due to the brain's ability to suppress one eye, double vision can appear to go away without medical evaluation or treatment. The causes of the double vision are very likely still present and loss of vision in one eye can occur due to lack of treatment. The loss of vision in one eye can be temporary or permanent depending on detection and treatment. It is in this way, that diplopia contributes to loss of depth perception and binocular vision, amblyopia (lazy eye), and/or strabismus (deviating eye).

Monocular diplopia
Diplopia can also occur when viewing with only one eye; this is called monocular diplopia, or where the patient perceives more than two images, monocular polyopia. In this case, the multiple vision can be caused by a structural defect in the vision system, such as cataracts, subluxation of the crystalline lens or Keratoconus causing irregularities in the refraction of light within the eye.

Temporary diplopia
Temporary diplopia can also be caused by intoxication from alcohol or head injuries, such as concussion. If temporary double vision does not resolve quickly, one should see an eye doctor immediately.

Treatment for binocular diplopia
Treatment for binocular diplopia includes prism lenses and/or vision therapy. Daily wear of prism lenses is the passive compensatory treatment. Vision therapy is an active treatment which retrains the visual and vestibular systems (brain, eye muscles, and body). Vision therapy may eliminate the need for daily wear of prism lenses.