A disorder characterized by double vision: Diplopia is a perception of two images when looking at an object, usually caused by temporary or permanent eye-muscle paralysis.

Normally, the brain fuses slightly different images from each eye by matching corresponding points on each retina; however, when an eye muscle is paralyzed, the image falls at a different point and the images do not correspond which causes diplopia

Diplopia may be an early symptom of botulism (acute poisoning) or myasthenia gravis (disease characterized by progressive fatigue and generalized weakness of the skeletal muscles) and occurs in other infections, head injuries, and nerve or muscle disorders.

The normal visual reduplication of all objects seen at a distance other than at the point of fixation: A physiologic diplopia can be observed by holding two fingers in front of the eyes, one at six inches, and the other one at one foot away, and when that person just looks at either digit, the other one will be seen as two fingers.