title: Determining abnormal interocular latencies of multifocal visual evoked potentials.
abstract: OBJECTIVE
  To describe methods for measuring interocular latency differences of multifocal visual evoked potentials (mfVEP) and for determining regions with abnormal interocular latencies in patients.
  
  
  METHODS
  The mfVEPs from 100 individuals with normal visual fields and normal fundus examinations were analyzed. Individuals ranged in age from 21.6 to 92.4 years. The stimulus was a 60 sector, pattern-reversing dartboard display. Each sector had 16 checks, 8 white (200 cd/m2) and 8 black (< 1 cd/m2). Interocular latency was measured as the temporal shift producing the best cross-correlation value between the corresponding responses of each eye. The 'corrected interocular latency' was defined as the difference between this shift and the mean interocular latency (shift) for a particular sector and recording channel.
  
  
  RESULTS
  The variability of the corrected interocular latency decreased as the signal-to-noise ratio (SNR) of the mfVEP responses increased. For example, the 95% confidence intervals decreased from over 16 ms to under 4 ms as SNR increased. Grouping and summing the responses also lead to an increase in SNR and a decrease in the confidence interval. The results of various cluster criteria were also derived. A cluster criterion (e.g. two or more contiguous points within a hemisphere exceeding a given confidence interval), can serve to increase the specificity for detection of eyes or individuals with abnormal interocular latencies. For example, while 21% of the eyes had 3 or more points exceeding the 5% confidence interval, only 1.8% of the eyes had a cluster of 3 or more of these points. Finally, interocular latency was only weakly correlated with age (r = 0.26).
  
  
  CONCLUSIONS
  In testing for abnormalities in interocular latencies, the confidence interval should be based upon the SNR of the response. Grouping and summing responses to increase SNR or employing a cluster test may also prove useful.
authors.affiliation: Department of Psychology, Columbia University, New York, NY 10027-7004, USA. dch3@columbia.edu
authors.forename: Donald C
authors.initials: DC
authors.lastname: Hood
authors.forename: Xian
authors.initials: X
authors.lastname: Zhang
authors.forename: Christopher
authors.initials: C
authors.lastname: Rodarte
authors.forename: E Bo
authors.initials: EB
authors.lastname: Yang
authors.forename: Nitin
authors.initials: N
authors.lastname: Ohri
authors.forename: Brad
authors.initials: B
authors.lastname: Fortune
authors.forename: Chris A
authors.initials: CA
authors.lastname: Johnson
mesh_terms: D000208:Acute Disease; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D016001:Confidence Intervals; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications / Q000503:physiopathology; D009902:Optic Neuritis / Q000150:complications / Q000503:physiopathology; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results