title: Ophthalmological assessment of cannabis-induced persisting perception disorder: is there a direct retinal effect?
abstract: OBJECTIVE
  Cannabis is a psychotomimetic agent that induces impairment of sensory perception. We present detailed clinical and electrophysiological data of patients with hallucinogen persisting perception disorder (HPPD) after marijuana consumption.
  
  
  METHODS
  A HPPD patient and four heavy cannabis smokers with no visual disturbances (controls) underwent complete ophthalmological examination including psychophysical tests (visual acuity, color vision, visual field, and dark adaptation) and detailed electrophysiological examinations, including extended Ganzfeld ERG, multifocal ERG, and electrooculography (EOG). Furthermore, electrically evoked phosphene thresholds (EPTs) were measured to further evaluate retinal function.
  
  
  RESULTS
  Ophthalmological and most electrophysiological examinations were within normal limits for the HPPD patient and for all control subjects. Interestingly, EOG results of the HPPD patient showed a slightly reduced fast oscillation ratio, diminished standing potentials of the slow oscillations, and a light peak within normal range resulting in higher Arden ratios. The EPTs of the patient were reduced, in particular for pulses with long durations (50 ms) causing visual sensations even at lowest possible currents of the neurostimulator. The control subjects did not reveal such alterations.
  
  
  CONCLUSIONS
  Our findings suggest a direct effect of cannabinoids on the retina and retinal pigment epithelium function, which may be involved in disturbances of the visual function experienced after drug consumption. The observations presented here may contribute to the elucidation of the detailed mechanism. Furthermore, EOG and EPT measurements may be useful tools to demonstrate long-term retinal alterations in cannabis-induced HPPD in patients.
authors.affiliation: Institute for Ophthalmic Research, University of Tübingen, Schleichstr 12-16, 72076, Tübingen, Germany, ditta.zobor@uni-tuebingen.de.
authors.forename: Ditta
authors.initials: D
authors.lastname: Zobor
authors.forename: Torsten
authors.initials: T
authors.lastname: Strasser
authors.forename: Gergely
authors.initials: G
authors.lastname: Zobor
authors.forename: Franziska
authors.initials: F
authors.lastname: Schober
authors.forename: Andre
authors.initials: A
authors.lastname: Messias
authors.forename: Olaf
authors.initials: O
authors.lastname: Strauss
authors.forename: Anil
authors.initials: A
authors.lastname: Batra
authors.forename: Eberhart
authors.initials: E
authors.lastname: Zrenner
mesh_terms: D000328:Adult; D002188:Cannabis; D003623:Dark Adaptation; D004596:Electroretinography; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000503:physiopathology*; D008875:Middle Aged; D010468:Perceptual Disorders / Q000503:physiopathology*; D012160:Retina / Q000503:physiopathology; D055213:Retinal Pigment Epithelium / Q000503:physiopathology; D014786:Vision Disorders / Q000503:physiopathology*; D014792:Visual Acuity / Q000502:physiology; D014794:Visual Fields / Q000502:physiology; D055815:Young Adult