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.
Actavis appealed and in May a panel of the Second Circuit Court of Appeals upheld the injunction, and in June Actavis asked that its case be heard by the full Second Circuit panel. In August 2015, Actavis request was denied. Society and culture
Recreational use
One preclinical study on monkeys showed that memantine was capable of inducing a PCP-like intoxication. Because of its very long biological half-life, memantine was previously thought not to be recreational, although a few cases of sporadic recreational use have been described.A study examining self-reported use of memantine on the social network Reddit showed that the drug was used recreationally and as a nootropic, but also that it was misused in various illnesses as self-medication without strong scientific basis.