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“But I only drive to the shops…”

“But I only drive to the shops…”. Mr Javeed Khan Consultant Ophthalmologist St Mary’s Hospital Isle of Wight. Driving standards W hat is the evidence? Age and Driving Monocular drivers D ilated pupils. Do these patients need to notify DVLA?. 45 year old with ocular hypertension

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“But I only drive to the shops…”

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  1. “But I only drive to the shops…” Mr Javeed Khan Consultant Ophthalmologist St Mary’s Hospital Isle of Wight

  2. Driving standardsWhat is the evidence?Age and DrivingMonocular driversDilated pupils

  3. Do these patients need to notify DVLA? • 45 year old with ocular hypertension • 68 year old bilateral glaucomatous field loss • 75 year old with glaucoma, field defects in one eye only • Lorry driver on Latanoprost, mild field loss in one eye • Lorry driver with colour blindness • 42 year old with night blindness

  4. Driving is a demanding activity PERCEPTION Central Fixation Peripheral Scanning INTERPRETATION Reaction Time DECISION ACTION Motoring Ability

  5. Is Poor Visual acuity a contributory factor in road accidents?

  6. Is poor visual acuity a contributory factor in road accidents? From 2005 – 2009 nearly 700,000 accidents on UK roads • 0.4 % of fatal accidents and 0.2 % of all accidents due to ‘defective/uncorrected eyesight’

  7. How important is poor vision as a contributory factor in road accidents? From 2005 – 2009 nearly 700,000 accidents on UK roads • 0.4 % of fatal accidents and 0.2 % of all accidents due to ‘defective/uncorrected eyesight’ • Mobile phone use 0.2 % of all accidents

  8. How important is poor vision as a contributory factor in road accidents? From 2005 – 2009 nearly 700,000 accidents on UK roads • 0.4 % of fatal accidents and 0.2 % of all accidents due to ‘defective/uncorrected eyesight’ • Mobile phone use 0.2 % of all accidents • ‘Failed to look properly’ 20% of fatal and 35% of all accidents • Vision affected by sun/headlights/dirty windscreen 3.5%

  9. VISUAL STANDARDS FOR DRIVING With both eyes open and with the aid of glasses or contact lenses if worn: • Can read number plate at 20 metres in good daylight • Snellen visual acuity 6/12 or better

  10. Group 2 (Lorry, Bus) Snellen visual acuity: • Better eye 6/7.5 • Before 2012: Worse eye to be at least 6/9 • Now 6/60 acceptable in worse eye • No minimum uncorrected visual acuity • But glasses no more than + 8 dioptres

  11. Case • Lorry driver develops posterior sub-capsular cataract in left eye, Right eye pseudophakic • VA: • Right eye: 6/6 unaided • Left eye: 6/36 unaided no improvement • Both eyes open: 6/6 • Patient doesn’t complain of glare, has full fields Can he continue to drive his lorry while waiting for cataract surgery? Yes, as long as no other visual impairment

  12. Evidence for visual acuity standard:Why 6/12 on Snellen? In 1937 standard introduced: Number plate at 75 feet (23 metres) Equal to stopping distance at 30 mph

  13. Evidence for visual acuity standard • As number plate sizes changed distance changed: • 20.5 metres pre-2001 • 20 metres Current

  14. Evidence for visual acuity standard:Why 6/12 on Snellen? • Drasdo and Haggerty 1983: • Approximates to 6/9-2 or 6/10 based on their statistical model • Charman 1997: • Calculated Snellen equivalent as 6/15 based on angular subtense (13.4 minutes of arc) • Current standard 6/12

  15. How reliable is the Snellen standard in predicting number plate test results? • Currie et al BJO 2000 • 100 patients with vision 6/9 or 6/12 • Ability to read number plate tested • 26 % of 6/9 FAILED and 34% of 6/12 PASSED

  16. Number plate difficulty P610VOH M528CBY T174ILE M528CBY T174ILE P610VOH Kiel et al 2003 McMonnies 1999 (Chart construction and letter legibility)

  17. Does poor visual acuity cause accidents?

  18. Is there a link between poor visual acuity and accidents? The evidence is WEAK from studies of accidents Greater likelihood of involvement in more than 1 accident if VA poor (Hofstetter et al 1976) Weak correlation between driving and VA (Burg et al 1976)

  19. Is there a link between poor visual acuity and accidents? Studies of accidents: Studies not big enough to pick up statistical difference • Motor accidents are rare Owens et al: not likely to fall victim to fatal accident if drive for 3738 years • Extremes of vision in drivers is rare • People exhibit adaptive behaviour • Confounding variable e.g. glare from cataract

  20. Is there a link between poor visual acuity and accidents? Studies on closed road circuits: • Poor acuity affected sign recognition and hazard avoidance • Increased time to complete circuit But • No impact on manoeuvring ability or maintaining lane position Studies on simulators • In different conditions: support the findings from closed circuit studies

  21. Is there a link between poor visual acuity and accidents? Effect of Legislation: In Florida mandatory rescreening introduced for over 80s Those that failed were given an opportunity to correct vision (glasses, cataract surgery etc.) Most were able to go back to driving after correction After 3 years: Accident fatality rates in over 80s fell by 17%

  22. Case • Patient has cataracts • VA: • Right eye: 6/18, Left eye: 6/24 • Both eyes open: 6/12-3 • Patient can read number plate in good light at 20 metres What must the patient do? Stop driving Offer to surrender license to DVLA Apply for restoration after successful cataract surgery

  23. Is there a link between visual field loss and accidents?

  24. Evidence for Visual Fields and accidents • People with visual field defects have DOUBLE the number of accidents/traffic violations • Half of the people with field loss were unaware of problems with peripheral vision • Johnson and Keltner (1983) in a study of 10,000 drivers

  25. Evidence for Visual Fields and accidents • Visual field size best predictor of real-world and simulator crashes and driving performance • Especially defects within 100 degrees • But actual cut-off value for standards is unclear

  26. VISUAL FIELDS Tested with: • Target equivalent to white, Goldmann III4e settings • Esterman binocular field (sometimes Monocular fields exceptionally Goldmann) • False positive no more than 20%

  27. Esterman Binocular Field 120 pointsSuprathreshold 10dB

  28. Esterman Binocular Field 350 Horizontally +/- 75 degreesSuperior 35 degreesInferior 55 degrees 550

  29. Esterman • Central +/- 20 degrees Sparse12 points above and 22 below fixation

  30. VISUAL FIELDS STANDARDS: • Field of at least 120 degrees on the horizontal • Minimum 50 degrees to left and right

  31. 750 450 600 600 500 700

  32. VISUAL FIELDS STANDARDS: • No significant defect in central 20 degrees of fixation above and below horizontal

  33. Central defects • Allowed • Scattered single missed points • Single cluster of up to 3 adjoining points

  34. Central defects • Not Allowed • Cluster of 4 even partly within central 20 degrees • Cluster of 3 and additional single • Central extension of hemianopia/quadrantonopia greater than 3 points

  35. Peripheral defects Allowed Cluster of 3 on or across horizontal

  36. Limit of field measured at this point (750) Limit of field measured at this point (500)

  37. Peripheral defects Allowed Cluster of 3 on or across horizontal Vertical defect of any length but single point width cutting across horizontal

  38. Limit of field measured at this point (500) Limit of field measured at this point (750)

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