title: Multifocal visual evoked potentials are influenced by variable contrast stimulation in MS.
abstract: OBJECTIVE
  To test the hypothesis that patients with multiple sclerosis (MS) with intereye asymmetry on low contrast letter acuity, and thickness of the retinal nerve fiber layer (RNFL), would exhibit corresponding changes in cortical timing and amplitude responses on pattern reversal multifocal visual evoked potentials (mfVEP), contingent upon variable stimulus contrast.
  
  
  METHODS
  In a cross-sectional study, we investigated a cohort of 11 normal subjects and 40 patients with MS, 21 of whom had a history of acute optic neuritis (MS-AON) with an intereye asymmetry with respect to RNFL thickness, and on low contrast letter acuity performance. Pattern reversal mfVEP was performed at high (100%), low (33.3%), and very low (14.2%) Michelson-contrast levels.
  
  
  RESULTS
  Compared to baseline measures at 100% contrast, the mean amplitude of the mfVEP was reduced in MS-AON eyes, upon pattern-reversal stimulation at the 2 lower contrast levels (p < 0.0001). With respect to changes in timing responses, the intereye asymmetry was increased in the MS-AON patients upon lower contrast pattern-reversal stimulation (p < 0.0001 for 33.3% compared to 100%, and p < 0.001 for 14.2% compared to 100%). The fellow eye in 12 (57%; p < 0.001) of the patients with an abnormal eye, and a history of AON, revealed abnormal amplitude and timing responses upon low contrast stimulation (signifying unmasking of occult damage).
  
  
  CONCLUSIONS
  Our findings support the hypothesis that mfVEP metric abnormalities are contingent upon contrast magnitude during pattern reversal stimulation. Further, this paradigm was capable of unmasking occult abnormalities in a significant number of apparently unaffected eyes.
authors: Department of Neurology & Neurotherapeutics, University of Texas Southwestern Medical Center at Dallas, Dallas, USA.
authors: Audrey R
authors: AR
authors: Frohman
authors: Zane
authors: Z
authors: Schnurman
authors: Amy
authors: A
authors: Conger
authors: Darrel
authors: D
authors: Conger
authors: Shin
authors: S
authors: Beh
authors: Benjamin
authors: B
authors: Greenberg
authors: Erich
authors: E
authors: Sutter
authors: Peter A
authors: PA
authors: Calabresi
authors: Laura J
authors: LJ
authors: Balcer
authors: Teresa C
authors: TC
authors: Frohman
authors: Elliot M
authors: EM
authors: Frohman
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009103:Multiple Sclerosis / Q000150:complications / Q000503:physiopathology*; D009412:Nerve Fibers / Q000473:pathology / Q000502:physiology; D009902:Optic Neuritis / Q000150:complications / Q000503:physiopathology*; D010775:Photic Stimulation / Q000379:methods; D012165:Retinal Ganglion Cells / Q000473:pathology / Q000502:physiology; D041623:Tomography, Optical Coherence / Q000379:methods; D014792:Visual Acuity / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology