Double vision is the experience of seeing duplicated vision,   similar to when one crosses their eyes. Depending on the intensity, this effect can result in a reduced ability to function and perform basic tasks that necessitate the use of sight.
The effect can easily be suppressed by closing one eye. This suggests that double vision may occur when the brain overlays the data received from both eyes on top of each other incorrectly, failing to properly merge the information into a singular 3-dimensional image as it normally would during everyday life.
This effect is capable of manifesting across the 3 different levels of intensity described below:
Double vision is often accompanied by other coinciding effects, such as visual acuity suppression and visual agnosia. This effect is most commonly induced under the influence of moderate dosages of depressant and dissociative compounds, such as alcohol, quetiapine, ketamine, and DXM.  However, it can also occur much less consistently under a wide range of other classes of compounds, such as hallucinogens, stimulants, anticholinergics, SSRIs, opioids, GABAergics, and cannabinoids.
- Marsh, A. (1979). Visual hallucinations during hallucinogenic experience and schizophrenia. Schizophrenia Bulletin, 5(4), 628. | https://doi.org/10.1093/schbul/5.4.627
- Smith, J. L., & Buncic, J. R. (1999). Drugs which can affect near vision: a useful list. American Orthoptic Journal, 49, 180-190. | https://uwpress.wisc.edu/journals/pdfs/AOJ_49_178.pdf