Diplopia, commonly known as double vision, is the simultaneous perception of two images of a single object. These images may be displaced horizontally,vertically, or diagonally (i.e. both vertically and horizontally)
in relation to each other.
Diplopia has a diverse range of neoplastic, opthalmologic, infectious,autoimmune, neurological causes.
Binocular diplopia is double vision arising as a result of the misalignment of the two eyes relative to each other. In such a case while the fovea of one eye is directed at the object of regard, the fovea of the other is directed elsewhere,and the image of the object of regard falls on an extra- foveal area of retina.
The brain calculates the 'visual direction' of an object based upon the position of its image relative to the fovea. Images falling on the fovea are seen as being directly ahead, while those falling on retina outside the fovea may be seen as above, below, right or left of straight ahead depending upon the area of retina stimulated. Thus, when the eyes are misaligned, the brain will perceive two images of one target object, as the target object simultaneously stimulates different, non-corresponding, retinal areas in either eye, thus producing double vision.
This correlation of particular areas of the retina in one eye with the same areas in the other is known as retinal correspondence. This relationship also gives rise to an associated phenomenon of binocular diplopia, although one that is rarely noted by those experiencing diplopia: Because the fovea of oneeye corresponds to the fovea of the other, images falling on the two fovea's projected' to the same point in space. Thus, when the eyes are misaligned, the brain will 'project' two different images in the same visual direction. This phenomenon is known as 'Confusion'.
Double vision is dangerous to survival, therefore, the brain naturally guards against its occurrence. In an attempt to avoid double vision, the brain can sometimes ignore the image from one eye; a process known as suppression.The ability to suppress is to be found particularly in childhood when the brains still developing. Thus, those with childhood strabismus almost never complain of diplopia while adults who develop strabismus almost always do. While this ability to suppress might seem a wholly positive adaptation to strabismus, in the developing child this can prevent the proper development of vision in the affected eye resulting in amblyopia.Some adults are also able to suppress their diplopia, but their suppression israrely as deep or as effective and takes longer to establish. They are not atrisk of permanently damaging their vision as a result though. It can appear sometimes,therefore, that diplopia disappears without medical intervention. However, in some cases the cause of the double vision may still be present.
More rarely, diplopia can also occur when viewing with only one eye; thisis called monocular diplopia,or, where the patient perceives more than two images, monocular polyopia.
Temporary diplopia can be caused by intoxication from alcoholor head injuries, such as concussion. If temporary double vision does not resolve quickly, one should see an ophthalmologist immediately. It can also be a side effect of the anti-epileptic drugs, and the anti-convulsion drug, as well as the hypnotic drug and the dissociative drugs.Temporary diplopia can also be caused by tired and/or strained eye muscles, orby one crossing their own eyes at will. If diplopia appears with other symptoms such as fatigue and acute or chronic pain, the patient should see a doctor immediately.