title: Sensitivity and specificity of the step VEP in suspected functional visual acuity loss.
abstract: OBJECTIVE
  Early and accurate diagnosis of functional visual loss (FVL) allows optimum management. Visual evoked potentials (VEPs) offer a means of objectively estimating acuity and therefore could assist with early and accurate diagnosis. The aim of this study was to assess the sensitivity and specificity of the step VEP in diagnosing FVL.
  
  
  METHODS
  A retrospective audit was conducted in 36 school-aged children presenting with reduced visual acuity and clinical suspicion of FVL. All had undergone step VEP testing as part of their investigation. Medical notes were reviewed, and where necessary, referring centres, general practitioners or electronic clinical portals were consulted to obtain longer-term outcome data.
  
  
  RESULTS
  Twenty-seven of the 36 patients (75%) were classified as having had FVL: all had a normal step VEP spatial threshold. Nine patients (25 %) had an organic cause for their acuity loss, of whom seven had abnormal step VEP spatial thresholds: the other two patients had some functional overlay to their organic disease. The step VEP sensitivity was 78% (95% confidence interval 40-96%), and specificity was 100% (95% confidence interval 84-100%).
  
  
  CONCLUSIONS
  The high specificity of the step VEP for FVL warrants increased suspicion of an organic cause should the step VEP spatial threshold be abnormal.
authors.affiliation: Department of Clinical Physics and Bio-engineering, Royal Hospital for Sick Children, Dalnair Street, Glasgow G3 8SJ, UK. ruth.hamilton@glasgow.ac.uk
authors.forename: Ruth
authors.initials: R
authors.lastname: Hamilton
authors.forename: Michael S
authors.initials: MS
authors.lastname: Bradnam
authors.forename: Gordon N
authors.initials: GN
authors.lastname: Dutton
authors.forename: Anna L
authors.initials: AL
authors.lastname: Lai Chooi Yan
authors.forename: Tim E
authors.initials: TE
authors.lastname: Lavy
authors.forename: I
authors.initials: I
authors.lastname: Livingstone
authors.forename: Alison M
authors.initials: AM
authors.lastname: Mackay
authors.forename: Jane R
authors.initials: JR
authors.lastname: Mackinnon
mesh_terms: D002648:Child; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014786:Vision Disorders / Q000175:diagnosis* / Q000503:physiopathology; D014792:Visual Acuity