title: Impact of superior and inferior visual field loss on hazard detection in a computer-based driving test.
abstract: OBJECTIVE
  Binocular visual field (VF) loss is linked to driving impairment, guiding authorities to implement fitness to drive requirements for VFs. Yet, evidence is limited regarding the specific types of VF defect that impede driving. This study used a novel gaze-contingent display to test the hypothesis that superior VF loss impacts detection of driving hazards more than inferior loss.
  
  
  METHODS
  The Hazard Perception Test (HPT) is a computer-based component of the UK examination for learner drivers. It measures the response rate for detecting hazards in a series of real-life driving films, yielding a score out of 75, calculated based on the efficiency of detecting 15 hazards. Thirty UK drivers with healthy vision completed three versions of the HPT in a random order. In two versions, a computer set-up incorporating an eye-tracker modified a simulated VF defect in the superior and inferior VFs, respectively, according to the users' real-time gaze as they completed the HPT. The other version was unmodified to measure the baseline performance.
  
  
  RESULTS
  Participants' mean score at baseline was 49/75 (SD=9). Mean (SD) performance fell by 18% (40(11)) when viewing films with a superior defect and 12% with an inferior defect (43(10)). These average differences were statistically significant (p<0.001; 95% CI for mean difference=1-7) CONCLUSIONS: In this study, simulated VF defects impaired the ability to detect driving hazards relative to participants' normal performances, with superior defects having more impact than inferior defects. These results could help inform the design of fairer tests of the VF component for fitness to drive.
authors.affiliation: Division of Optometry and Visual Science, School of Health Sciences, City University London, London, UK.
authors.forename: Fiona C
authors.initials: FC
authors.lastname: Glen
authors.affiliation: Division of Optometry and Visual Science, School of Health Sciences, City University London, London, UK.
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Smith
authors.affiliation: Division of Optometry and Visual Science, School of Health Sciences, City University London, London, UK.
authors.forename: David P
authors.initials: DP
authors.lastname: Crabb
mesh_terms: D000063:Accidents, Traffic / Q000517:prevention & control*; D000328:Adult; D001333:Automobile Driver Examination; D001334:Automobile Driving; D001364:Awareness; D003198:Computer Simulation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012449:Safety; D014786:Vision Disorders / Q000503:physiopathology*; D014792:Visual Acuity / Q000502:physiology; D014794:Visual Fields / Q000502:physiology*
keywords: Field of vision; Glaucoma