title: Conducting shorter VEP tests to estimate visual acuity via assessment of SNR.
abstract: BACKGROUND
  The estimation of visual acuity (VA) via visual evoked potentials (VEP) is a valuable measure for all preverbal and non-verbal subjects whether adults or children. The aim of this study is to introduce a novel technique of VEP acquisition based on estimates of signal-to-noise ratio (SNR) and comparison to a predefined detection threshold. We aim to demonstrate the reduction in total study time without compromising the accuracy of the VEP-determined acuity estimate.
  
  
  METHODS
  The VEP-determined acuity of twelve normal subjects was assessed via a spatial frequency (SF) sweep. A pattern reversal checkerboard stimulus utilised SFs ranging from 0.1 to 28 cycles per degree (cpd). Using linear extrapolation and Bland-Altman analysis, VEP-acquired acuity was compared to a conventional Snellen Acuity measurement. An SNR test, Fsp, assessed signal quality to determine the minimum amount of sweep data required for VEP-based VA estimation.
  
  
  RESULTS
  VEP acuity estimates correlated strongly (r2=0.91, SD=0.06), leading to a VA limit via extrapolation. Bland-Altman analysis revealed agreement between tests is statistically valid (95% CI -0.11 to 0.42 logMAR). The Fsp statistic indicated SFs 1.3-3.6 cpd yielded Fsp>3.1 within 15 s of acquisition with frequencies>3.6 cpd being sub-threshold. The Kruskal-Wallis statistic compared final Fsp values for SFs as groups, where F=208.82 ranking each frequency, with frequencies>7.2 cpd ranking lowest.
  
  
  CONCLUSIONS
  The Fsp as an SNR measurement shows that rapid, quality-driven clinical tests for VEP-based acuity estimates can be conducted without compromising accuracy.
authors.affiliation: School of Information Technology and Electrical Engineering, University of Queensland, Queensland, Australia, kartik.iyer@uqconnect.edu.au.
authors.forename: Kartik K
authors.initials: KK
authors.lastname: Iyer
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Bradley
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Wilson
mesh_terms: D000293:Adolescent; D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation; D012016:Reference Values; D014792:Visual Acuity; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult