title: Assessment of patients with suspected non-organic visual loss using pattern appearance visual evoked potentials.
abstract: BACKGROUND
  The aim of the study was to validate the use of the short duration pattern onset visual evoked potential (PappVEP) in the objective assessment of visual acuity (VA) in patients referred with presumed non-organic visual loss.
  
  
  METHODS
  The combination of minimum check size and minimum contrast required to elicit a consistently discernible PappVEP (amplitude >or=5 microV) were measured in ten normal subjects under conditions of induced optical blur (0 to +3 dioptres) and the relationship to Snellen VA established. The data from 100 consecutive patients (167 eyes) referred for possible non-organic visual loss (NOVL) and 20 patients with confirmed visual pathway dysfunction were reviewed in relation to the results in normal subjects.
  
  
  RESULTS
  Snellen VA, under conditions of blur, could be predicted in normal subjects from the check size and contrast required to elicit a criterion PappVEP. These data were tabulated and a quantitative guideline established for the estimation of VA in the patients referred with suspected NOVL. Most (88%) patients referred with suspected NOVL had normal electrophysiology and PappVEPs consistent with normal Snellen VA. In others, they suggested a degree of non-organic overlay. In 20 cases of organic visual loss, PappVEPs were in close agreement with subjective VA.
  
  
  CONCLUSIONS
  The short duration pattern onset visual-evoked potential is confirmed as a clinically useful tool in the objective assessment of patients with suspected non-organic visual loss.
authors.affiliation: Department of Electrophysiology, Moorfields Eye Hospital, London, EC1V 2PD, UK. v.a.mcbain@abdn.ac.uk
authors.forename: Vikki A
authors.initials: VA
authors.lastname: McBain
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Robson
authors.forename: Chris R
authors.initials: CR
authors.lastname: Hogg
authors.forename: Graham E
authors.initials: GE
authors.lastname: Holder
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D015350:Contrast Sensitivity / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014786:Vision Disorders / Q000503:physiopathology*; D014792:Visual Acuity / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology; D014795:Visual Pathways / Q000503:physiopathology*