Thus, when the eyes are misaligned, two different objects will be perceived as superimposed in the same space. This phenomenon is known as visual confusion.The brain naturally guards against double vision. 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 brain is 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 an entirely 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 is rarely as deep or as effective and takes much longer to establish,  thus they are not at risk of permanently compromising their vision. In some cases, diplopia disappears without medical intervention, but in other cases, the cause of the double vision may still be present. Certain people with diplopia who cannot achieve fusion and yet do not suppress may display a certain type of spasm-like irregular movement of the eyes in the vicinity of the fixation point (see: Horror fusionis). Monocular
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.
While serious causes rarely may be behind monocular diplopia symptoms, this is much less often the case than with binocular diplopia. The differential diagnosis of multiple image perception includes the consideration of such conditions as corneal surface keratoconus, subluxation of the lens, a structural defect within the eye, a lesion in the anterior visual cortex, or nonorganic conditions, but diffraction-based (rather than geometrical) optical models have shown that common optical conditions, especially astigmatism, can also produce this symptom. Temporary
Temporary binocular diplopia can be caused by alcohol intoxication or head injuries, such as concussion (if temporary double vision does not resolve quickly, one should see an optometrist or ophthalmologist immediately). It can also be a side effect of benzodiazepines or opioids, particularly if used in larger doses for recreation, the antiepileptic drugs phenytoin and zonisamide, and the anticonvulsant drug lamotrigine, as well as the hypnotic drug zolpidem and the dissociative drugs ketamine and dextromethorphan. Temporary diplopia can also be caused by tired or strained eye muscles. If diplopia appears with other symptoms such as fatigue and acute or chronic pain, the patient should see an ophthalmologist immediately. Voluntary
Some people are able to consciously uncouple their eyes, either by overfocusing closely (i.e. going cross-eyed) or unfocusing. Also, while looking at one object behind another object, the foremost objects image is doubled (for example, placing ones finger in front of ones face while reading text on a computer monitor). In this sense, double vision is neither dangerous nor harmful, and may even be enjoyable.