Editing Optical illusion (section)

== Pathological visual illusions (distortions) ==
A [[pathology|pathological]] visual illusion is a distortion of a real external stimulus<ref name=Pelak>{{cite web|last1=Pelak|first1=Victoria|title=Approach to the patient with visual hallucinations|url=http://www.uptodate.com/contents/approach-to-the-patient-with-visual-hallucinations|website=www.uptodate.com|access-date=2014-08-25|url-status=live|archive-url=https://web.archive.org/web/20140826120056/http://www.uptodate.com/contents/approach-to-the-patient-with-visual-hallucinations|archive-date=2014-08-26}}</ref> and is often diffuse and persistent. Pathological visual illusions usually occur throughout the visual field, suggesting global excitability or sensitivity alterations.<ref name=Gersztenkorn>{{cite journal|last1=Gersztenkorn|first1=D|last2=Lee|first2=AG|title=Palinopsia revamped: A systematic review of the literature|journal=Survey of Ophthalmology|date=Jul 2, 2014|pmid=25113609|doi=10.1016/j.survophthal.2014.06.003|volume=60|issue=1|pages=1–35}}</ref> Alternatively visual hallucination is the perception of an external visual stimulus where none exists.<ref name=Pelak /> Visual hallucinations are often from focal dysfunction and are usually transient.

Types of visual illusions include [[oscillopsia]], [[halo (optical phenomenon)|halos around objects]], [[illusory palinopsia]] ([[illusory palinopsia#Visual trailing|visual trailing]], [[illusory palinopsia#Light streaking|light streaking]], [[Illusory palinopsia#Prolonged indistinct afterimage|prolonged indistinct afterimages]]), [[akinetopsia]], [[visual snow]], [[micropsia]], [[macropsia]], [[teleopsia]], [[pelopsia]], [[metamorphopsia]], [[dyschromatopsia]], intense [[glare (vision)|glare]], [[blue field entoptic phenomenon]], and [[entoptic phenomena|purkinje trees]].

These symptoms may indicate an underlying disease state and necessitate seeing a medical practitioner. Etiologies associated with pathological visual illusions include multiple types of [[eye disease|ocular disease]], [[migraine]]s, [[hallucinogen persisting perception disorder]], [[closed head injury|head trauma]], and [[prescription drug]]s. If a medical work-up does not reveal a cause of the pathological visual illusions, the idiopathic visual disturbances could be analogous to the altered excitability state seen in visual aura with no migraine headache. If the visual illusions are diffuse and persistent, they often affect the patient's quality of life. These symptoms are often refractory to treatment and may be caused by any of the aforementioned etiologies, but are often idiopathic. There is no standard treatment for these visual disturbances.