title: The monocular vertical prism dissociation test.
abstract: OBJECTIVE
  To determine if the monocular vertical prism dissociation test can differentiate between organic and nonorganic visual loss.
  
  
  METHODS
  A prospective, single-masked observational study.
  
  
  METHODS
  Three institutional neuro-ophthalmology practices. Group 1 consisted of 30 normal controls. Group 2 included 30 patients with known organic visual loss. Group 3 contained 35 patients with suspected nonorganic monocular visual loss. Participants were asked to describe what they saw while viewing a single Snellen letter when a 4-prism diopter base-down prism was placed in front of their better eye. Outcome was measured by whether the participant sees one or two letters with the prism in place.
  
  
  RESULTS
  Vision-appropriate results were given by all members of Group 1 (two images) and by all members of Group 2 (one image). Two images were seen by 31 of 35 members of Group 3, indicating nonorganic visual loss. The other 4 subjects in Group 3 saw one image; each was subsequently found to have occult pathology.
  
  
  CONCLUSIONS
  The vertical prism test quickly differentiates organic from nonorganic monocular visual acuity loss.
authors.affiliation: Department of Ophthalmology, Neurology, Neurosurgery, University of Cincinnati and The Cincinnati Eye Institute, Cincinnati, Ohio, USA. kgolnik@cinci.rr.com
authors.forename: Karl C
authors.initials: KC
authors.lastname: Golnik
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Lee
authors.forename: Eric R
authors.initials: ER
authors.lastname: Eggenberger
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D006801:Humans; D008306:Malingering / Q000175:diagnosis; D008875:Middle Aged; D011446:Prospective Studies; D016037:Single-Blind Method; D014786:Vision Disorders / Q000175:diagnosis*; D014787:Vision Tests / Q000379:methods*; D014792:Visual Acuity