title: Objective VEP perimetry in glaucoma: asymmetry analysis to identify early deficits.
abstract: OBJECTIVE
  The multifocal visual evoked potential (VEP) shows markedly symmetrical responses between the two eyes of control subjects. Patients with glaucoma and patients considered at high risk for glaucoma were examined to determine if VEP asymmetry could be identified and used for diagnosis and detection of early damage.
  
  
  METHODS
  Multifocal pattern VEP recordings were performed using a single channel bipolar occipital electrode position and the Visual Evoked Response Imaging System (VERIS). There were 125 subjects: 24 control subjects, 70 patients with glaucoma, and 31 patients considered at high risk for glaucoma. A between-eye relative asymmetry coefficient (RAC) was determined for each of the 60 test points in the VEP field. The RAC for patients with glaucoma and patients considered at risk for glaucoma were compared with values from control subjects. Correlation between Humphrey thresholds and RAC scores was performed.
  
  
  RESULTS
  Patients with glaucoma and patients considered at risk for glaucoma both showed significantly larger mean quadrant RAC values. When point by point analysis was performed, 69 out of 70 scotomas were identified with a cluster of at least 3 points of P < 0.05. For those considered at high risk for glaucoma, 10 out of 31 patients had abnormal areas in the VEP field. There was a strong correlation (r = 0.82) between quadrantic RAC mean values and Humphrey quadrant threshold scores in an asymmetric glaucoma subgroup. Abnormal VEP responses were identified in parts of the visual field that were still normal on perimetry.
  
  
  CONCLUSIONS
  Asymmetry analysis correctly identifies patients with glaucomatous field loss and shows abnormalities in many patients considered at high risk for glaucoma who still have normal fields. Asymmetry analysis is able to identify objectively the extent of glaucomatous damage and may be able to detect changes before subjective field loss occurs.
authors.affiliation: Save Sight Institute, Department of Ophthalmology, Sydney University, NSW, Australia.
authors.forename: S L
authors.initials: SL
authors.lastname: Graham
authors.forename: A I
authors.initials: AI
authors.lastname: Klistorner
authors.forename: J R
authors.initials: JR
authors.lastname: Grigg
authors.forename: F A
authors.initials: FA
authors.lastname: Billson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002908:Chronic Disease; D018450:Disease Progression; D005074:Evoked Potentials, Visual; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D015203:Reproducibility of Results; D014786:Vision Disorders / Q000175:diagnosis* / Q000503:physiopathology; D058609:Visual Field Tests / Q000379:methods*; D014794:Visual Fields