Simulator based assessment
of drivers with visual field
defects
Björn Peters, VTI
Sweden – some basic facts
•
•
•
•
•
•
•
•
•
EU member state
EU driving license directive – specification
of minimum medical requirements
9.6 million inhabitants
6.1 million driving license group 1
1.6 million license holders +65 y
40 000 revoked licenses (all reasons)
(2013)
4 500 revoked licenses for medical
reasons annually (2013)
?? due to visual problem
100 applications for exemptions annually
Swedish requirements for peripheral visual
field Group I
Binocular Esterman screening test
2016-03-14
3
Swedish requirements for central visual field
Group I
Static threshold perimetry (Humphrey 24-2 or equivalent)
Within 10° from fixation:
Threshold in each
corresponding test
point should be 20 dB
or more
Within 20° from fixation:
Threshold in each
corresponding test
point should be 10 dB
or more (one missing
point is accepted)
2016-03-14
4
≥10 dB
≥20 dB
The process in Sweden
•
•
•
•
Mandatory for all physicians to report if medical requirement
not fulfil or agree with the patient to refrain from driving
(written consent)
Swedish Transport Agency (STA) decides if requirements
fulfilled –> OK, If not -> revoked license
Agree -> apply for exemption or Disagree -> appeal in court 3
levels
Apply for exemption -> added evidence of fitness to drive
required e.g.
• Simulator Based Assessment in Norway - SINTEF
• On-road assessment not sufficient
• Demand for a new Simulator Based Assessment Method
 License with exemption – conditions can apply e.g. geographical
restrictions (2012 – 103, 2013 – 110)
Simulator test at SINTEF – reaction time
6 positions –
rural road 1
Press buttons to
respond
6 positions –
rural road 1
Results compared
to normative data
11 positions –
city road 1
Reaction times were recorded from 20 stimuli over a 15 minutes drive.
Stimuli size: 1. child head at 30 m, 2. adult body at 30 m,
Stimuli: duration 4 seconds
Developing a new assessment method at VTI
•
•
•
•
•
•
Aim: determine if a driver with a visual field loss can
compensate and drive equally well as a driver without field loss
Approach: develop a relevant and realistic diving task with
more or less critical situations and build a matched reference
database (100+)
Simulator: high end simulator, dynamic, good visual system
Consider: simulator sickness and test conditions
Output: certificate stating driving performance/ability
compared to normative data
Assessment Validity: continuous follow-up and improvements
Simulator based assessment - pros and cons
Strengths







High level of control
Good internal validity
Same conditions for all
Critical situations with no risk
Realistic compared to clinical
testing
Reliable S-R testing
Eye tracking feasible
Weaknesses





Simulator driving - 3D in a 2D
world
Speed perception not ideal –
offset
Situations simplified compared to
real life
External validity partly good –
follow up needed
Simulator sickness
VTI Driving Simulator IV - Volvo XC 60 cabin
Rear- and SideMirror Displays
4 Video
Cameras
Virtual
Cockpit
Display
Sound
System
Rexroth hexapod
X-Y Sled 2,3 * 2,5 m
5 Gaze Tracking
Cameras
Shaker
Force Feedback
Steering Wheel
Sim IV visual projection system


9x Epson EB-410W projectors
Mersive SOL software
 Auto calibration
 Edge blending
 Color correction

>180 degree field-of-view
Tillfälle att prova under dagen
Driving task and assesment criteria
• Approx. 50 km driving (rural, motorway, city)
• Critical situations (pedestrians, vehicles, bicycles, road works,
traffic light etc.)
• Assessment measures: speed, time, lateral position,
(collisions/incidents)
• Also: Time based safety margins (combination of TTC and THW)
• Reaction time to artificial stimuli (SINTEF like)
• Tentative assessment criteria exclude 2,5% of “low performers”
(previously used at SINTEF) - several measures
Tool for development, runs on a PC
SINTEF test - proposal
•
•
•
•
Motive: compare data with SINTEF and other studies
Stimuli as SINTEF – traffic signs in 6 different positions
(false and true (STOP sign))
Simultaneous stimuli – right/left – controlling for over
compensation
Two buttons on the steering wheel
• One true stimuli (also combination with false) – press one button
• Two true stimuli – press two buttons
• One single or two false stimuli – press no buttons
•
•
•
Separate part of the driving task
Clear written and oral instructions
Training before
Defining assessment criteria – a difficult task
 Considering own and other road users’ safety
 Not restrict if driving ability deemed sufficient
 No solid scientific evidence for how much we need to see
in order to drive safely
 Other examples
Alcohol (BAC - 0,2‰) fixed – should it be differentiated?
Deafness OK to drive – why?
Epilepsy – OK with medication and no seizure for 3 months
Dementia – when is the right time to stop?
Mobility impairments – what is sufficient adaptation?
 Whatever we do we need to follow-up!
Visual and cognitive tests
•
•
•
•
•
•
•
•
•
Visual acuity
Visual field of view test - Humphrey
Useful Field of View (UFOV)
Trail Making Test (TMT A&B)
Dynamic TMT (New)
Perceptual speed (Operative)
Attentional demanding (Operative/Tactical)
Working memory (Tactical/strategic)
Meta memory (Strategic)
Useful field of view (UFOV)
Dynamic Trail Making Test
Persons with visual field defects interested to
participate
Until 15 April 222 interested
189 replied a short survey
Data for recruiting 100 reference drivers
Most have sent their visual field data
Select a small, relevant group of drivers to
participate in the project
• Delivery date mid - 2014
•
•
•
•
•
Age, gender, experience for selection of
reference drivers
Age
18-24
25-34
35-44
45-54
55-64
65-74
75Total
Male Female Total
4
1
5
1
1
2
12
9
21
22
5
27
36
8
44
63
2
65
25
0
25
163
26
189
Most male,
< 70% 55 +
Age
18-24
25-34
35-44
45-54
55-64
65-74
75Totalt
Num
5
2
21
27
44
65
25
189
Median distance
km/week
40,0
202,5
250,0
300,0
200,0
200,0
150,0
200,0
Min 10000 km/y
Max 25000 km/y
Diagnoses
Diagnosis,
free
Stroke
Glaucoma
Diabetes
Eye injury
Brain tumor
Other
Total
Missing
Totalt
Num
69
60
21
17
7
4
178
11
189
%
36,5
31,7
11,1
9,0
3,7
2,1
94,2
5,8
100,0
% of those
with a
diagnosis
38,8
33,7
11,8
9,6
3,9
2,2
100,0
Cumulative % of
those with a
diagnosis
38,8
72,5
84,3
93,8
97,8
100,0
Select based on diagnosis and visual
field defect
Difficult driving situations
Questions,
comments?