Visual field defects and accident risk, a retrospective study

1. 1 Visual field defects and accident risk, a retrospective study Gunnar D. Jenssen SINTEF

2. 2 Scope Evaluate how drivers passing the SINTEF simulator test the last 8 years have performed as drivers (accident history).  The SINTEF database includes prior medical evaluations, neuropsychological evaluations and on-road test results.  Find out which method, combination of methods and set out outcome parameters within each method, that is most predictive of driving ability and the associated risk for drivers with visual field defects.

3. 3 Previous studies Johnson & Keltner (1983) performed an automated visual field screening of 10000 volunteers. accident and conviction rates were more than twice as high as the control group. Results of subjects with visual field loss in one eye did not differ from their controls. Elvik, Mysen & Vaa (1997) A reduction of the active visual field with more than 40 % increases the accident rate dramatically. It is important to note that these results are for elderly drivers. Many of these elderly drivers had additional mental impairments (e.g. Alzheimer) which can increase accident risk in itself.

4. 4 Previous studies (accidents & behaviour) Coeckelbergh, (2001). Severe visual field defects have an impact on safety, and less severe visual field defects result in slower driving but otherwise unimpaired driving performance. Johnson & Keltner, (1983): Severe defects result in impaired driving performance defined by conviction and accident rates Wood & Troutbeck, (1992) Severe defects gave more manoeuvring errors, obstacle avoidance errors or less peripheral awareness. Szlyk, Seiple & Viana (1995) Reported that degree of central fields loss marginally predicted accidents. Szlyk et al, (1992). Assessment of driving performance in patients with retinitis pigmentosa and visual field defects demonstrate an increase in both accidents and driving performance errors in a simulator

5. 5 Compensation - (Pro) Szlyk et al, 1995; Wood & Troutbeck, 1992, 1994 : It is assumed that persons with less severe field defects have no impact on accidents because of compensatory mechanisms . These strategies can allow safe driving despite vision impairments. Szlyk et al, 1995 Compensatory mechanisms may be speed reduction, reduced risk-taking and L�vsund et al, 1991; Szlyk et al, 1995: Increase of eye movements

6. 6 Compensation - (Con) Hedin, (2001): Individuals with visual field defects usually deny having driving problems and argue that this is due to compensation with frequent eye and head movements Hedin & L�vsund (1987) concluded that they normally did not compensate. The simulator study compared drivers with visual field defects with normal drivers. The results indicate an increase in detection time when objects were presented in the blind areas. And in some cases the object was not discovered at all. L�vsund, Hedin & T�rnros (1991) reported that only 4 out of 31 subjects with visual field defects compensated. The study was based on a simulator study. The results indicate that the subjects who compensate concentrate much more fixations to the affected side of their field while driving.

7. 7 Purpose Provide evidence of accident risk associated with visual field defects. Establish better decision criteria for doctors in licensing assessment of drivers with visual field defects Assess the effectiveness of screening devices to test for visual field defects. Support future development of policy governing driver impairment with visual field defects.

8. 8 Method Inclusion criteria Tested in SINTEF simulator. Documentation of prior test results Goldman perimeter, medical evaluation, neuropsychological evaluation as well as on-road testing in traffic. Exclusion criteria Subjects showing indication of dementia or spatial hemi-neglect are excluded.

9. 9 Method Subjective and objective measures Questionnaires:Health, travel habits,, accidents, self perceived driving ability, driving problems, compensatory strategies In-depth interviews:To confirm answers and the course of possible accidents in order to reveal accident factors, which may be attributed to the visual field defect or insufficient compensatory behavior. Insurance reports:obtained to support analysis and confirm self reported accident history of the selected drivers.

10. 10 MethodSubjective and objective measures In addition all the 50 drivers were subject to a new: Medical examination Optometrical examination (Goldman & Ring perimeter etc) Test of visual functioning (acuity, contrast sensitivity, glare, etc) Neuropsychological tests Purpose: To document their current status, Check for possible changes in visual perceptual functions Control for conditions possibly affecting accident risk in the period between test and retest.

11. 11 Simulator SINTEF has developed a simulator test similar to the �Attentional Field of View� method (AFOV) which assess the drivers ability to detect briefly presented peripheral targets (traffic sign symbols) in the presence of a distracters and a central manoeuvring related task.  The simulator method allows free head movement and thus compensatory viewing behaviour not possible with traditional visual field testing (Goldman Perimeter or Useful Field of View test).

12. 12 The SINTEF video Simulator with graphic overlay symbols

13. 13 Response buttons

14. 14 Diagnosis and recommendation for drivers tested in the SINTEF driving simulator

15. 15 The visual system and associated visual field defects

16. 16 Sample Sample from SINTEF database 203 = Total number fitness to drive 1992-2000,  98 = Visual disturbance, without neglect and cognitive failure 34 = Not recommended 62 = Permission to drive Response rate Potential participants 62 4 = deceased 8 = unknown address Consent to study 50 2 = Illness (4%) 8 = work (16%) 5 = family (10%) 35 participants (70%)

17. 17 Sample N Age SD Sex Group 1 35 49 yrs 17 yrs 89% Male - 11% Female Exempted Licence Group 2 12 57 yrs 13 yrs 83 % Male - 17 % Female Not approved drivers Control group 143 47 yrs 25 yrs 52% Male - 48% Female Normal health

18. 18 Graphic sign symbols projected on the video in six different quadrants

19. 19 Neuropsychological Tests Trail Making Test A & B Similarities (item from WAIS) Block Design (item from WAIS) Wisconsin Card Sorting Test (WCST) CALCAP Trail Making Test A & B: Associated with psycho-motor problem solving, ability of visuo-spatial orientation and planning, and accomplishment of sequences. Part B is deemed to be most challenging, due to shifting between two sequences to finish (alphabet and numbers). The test is assumed sensitive of frontal lobe damages and degree of lateralisation. Similarities (item from WAIS): Item from the Weschler Adult Intelligence Scale, assumed to tap into ability of abstraction and concept formation. The item is also connected to logical and verbal reasoning. Block Design (item from WAIS): Item originating from Weschler Adult Intelligence Scale. The item is assumed to measure the ability of spatial organisation and visuo-spatial construction in which analysis of overall form in relation to parts is essential. Wisconsin Card Sorting Test (WCST): The test taps into central executive functions of the brain, presumed localized in the frontal cortex. WCST demands that the subject develops and sustains problem solving strategies, as well as being able to flexibly shift between these. The test affords strategic planning and the ability to utilize feedback. CALCAP: The test measures the subjects� mental speed under various conditions of informational processing and reaction times. Trail Making Test A & B: Associated with psycho-motor problem solving, ability of visuo-spatial orientation and planning, and accomplishment of sequences. Part B is deemed to be most challenging, due to shifting between two sequences to finish (alphabet and numbers). The test is assumed sensitive of frontal lobe damages and degree of lateralisation. Similarities (item from WAIS): Item from the Weschler Adult Intelligence Scale, assumed to tap into ability of abstraction and concept formation. The item is also connected to logical and verbal reasoning. Block Design (item from WAIS): Item originating from Weschler Adult Intelligence Scale. The item is assumed to measure the ability of spatial organisation and visuo-spatial construction in which analysis of overall form in relation to parts is essential. Wisconsin Card Sorting Test (WCST): The test taps into central executive functions of the brain, presumed localized in the frontal cortex. WCST demands that the subject develops and sustains problem solving strategies, as well as being able to flexibly shift between these. The test affords strategic planning and the ability to utilize feedback. CALCAP: The test measures the subjects� mental speed under various conditions of informational processing and reaction times.

20. 20 Driving Test under Supervision Motor Skills Ability to handle interior interface Movement Tempo Pace of actions Observational SkillsSituation awareness and attention Perceptual Skills Detection of stimuli Decision Making Skills Making and executing correct judgements Vehicle HandlingNavigating chosen course - adapting vehicle position Speed Regulation Adapting speed to environment Distinctness Communicating own driving behaviour to other vehicles Risk Perception Ability to perceive, evaluate and handle risk Empathic Reasoning Ability to take other drivers perspective in a situation Self Monitoring Insight and management in own strengths and weak points

21. 21 Visual Status Goldmann Perimeter Test Ophthimus automatic Ring perimeter. Psycho-physical assessments Ophtalmological and optometric evaluations

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24. 24 Exposure

25. 25 Travel exposure Light Daylight Darkness 62 % 38% Roads Rural roads Urban roads 39% 61% Season Summer Winter 55% 45%

26. 26 Travel habits

27. 27 Comparison of travel patterns by season

28. 28 Visual acuity The monocular and binocular visual acuity data were for most subjects within normal values. One subject had a maximum acuity of 0.12 at 40 cd/m2, the rest had acuity's above 0.6.

29. 29 Maximum contrast sensitivity (MCS) and integrated contrast sensitivity (ICS) were for most subjects within the normal range.

30. 30 Reaction time for different groups by visual square

31. 31 Driver performance The group of drivers not approved for holding a licence has longer reaction times than the driver with exempted licence Control group has shorter reaction times than the two patient groups. Drivers with exemption lay closer to the performance of the control group.

32. 32 Driver Performance: Neuropsychological Tests Group 1 consisting of drivers exempted licence was divided into 2 clusters by way of K-Means Cluster analysis of results on neuropsychological tests. Cluster A performed better on neuropsychological tests than Cluster B (F>6.9, p<.05). Comparing the two groups in terms of their driver performance showed no significant difference in reaction times.

33. 33 Driver performance - Age and gender The effect of age and gender on reaction times in each square was investigated by way of a General Linear Model (GLM). The results indicated that gender did not have en effect on reaction times in any of the squares (F<1.8, p>.05). Age proved to have an effect on all squares (F>5.6, p<.05), except �upper left� (F=2.775, p>.05) and �lower right� (F=.758, p>.1).

34. 34 What others think about my driving?

35. 35 Self reported accidents

36. 36 Accident risk - Insurance data Observed number of accidents Visual problems 15 Norm data 25  Observed number per 100.000 km Visual problems 0.89 Norm data 1.47 p<0.5, two-tailed t-test

37. 37 Visual Defects

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40. 40 Defects

41. 41 Compensation strategies

42. 42 Conclusions The results of this retrospective study of accident involvement of 35 visually impaired drivers exposed to normal traffic over a period varying from 3-8 years, shows that the selected subjects, drivers with visual field defects:

43. 43 Conclusions Drivers with visual field defects (Homonym Hemianopia, Quadrantanopia & Scotoma) do not differ significantly from the norm group in terms of insurance reported accidents or self reported accidents.  They do not compensate for their visual field defects by limiting their traffic exposure. The group of drivers not approved for holding a licence has longer reaction times than the driver with exempted licence, and the control group has shorter reaction times than the two patient groups. But drivers with exemption lay closer to the performance of the control group.  Drivers not approved have trouble compensating for their visual impairment in the driving simulator test. Drivers approved do compensate well for their visual impairment and have developed several conscious compensation strategies. Drivers approved are conscious about the consequences of their visual impairment and are motivated to drive safely.

44. 44 Conclusions This study shows drivers with even quite severe visual field defects e.g. homonymous heminopsia can drive with the same risk level as age, gender mileage and geographical area matched norm drivers without limiting neither mileage nor traffic exposure to potentially challenging traffic environments and traffic conditions.

45. 45 Conclusions This study supports previous findings that drivers with visual field defects may develop sufficient compensatory strategies and behaviour to drive safely (Coeckelbergh, 2001; Szlyk et al, 1995; Wood & Troutbeck, 1992, 1994,)

46. 46 The results from the SINTEF driving simulator, on road trials and interviews indicate that patients with visual field defects may consciously or unconsciously compensate with: Active search strategies and recheck in "blind" area before driving on. Use of mirrors Increased attention and situational awarenessb Observational Skills (situation awareness and attention) Perceptual Skills (detection of stimuli), Decision Making Skills (making and executing correct judgements) Vehicle Handling (navigating chosen course and adaptng vehicle position) Distinctness (communicating own driving behaviour to other vehicles) Risk Perception (ability to perceive, evaluate and handle risk) Empathic Reasoning (ability to take other drivers perspective in a situation) Self Monitoring (insight and management in own strengths and weak points)

47. 47 Conclusions Driving is a complex, multilevel task Neuropsychological tests tap into more basic and isolated mental capacities, The task in the driving simulator is a more complex and compounded one. Driving is not affected directly by the status of any specific ability (e.g. visual field defects, cognitive deficits, mental processing), but more an expression of a holistic organization of separate skills and abilities into a goal directed behaviour.

48. 48 Conclusions Assessment of driver skills cannot be concluded from neuropsychological tests or reaction times in simulation alone, rather, an overall appraisal seems more appropriate. Yet, some extreme scores on neuropsychological tests may be meaningful as contraindications of driver abilities (e.g. severe mental retardation, major defects of memory). The challenge in this sense will be to identify cut off scores for when the patient in question is not suited for driving. The main issue here is that the cut off score should reflect when the patient is not able to perform organizing and compensation strategies to outweigh his or hers defects, rather than driving abilities as such.

49. 49 Conclusions Weakness sample size Strength Response rate Multilevel study Control

50. 50 Acknowledgements