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

23-04-21 3

Binocular Esterman screening test

Swedish requirements for central visual fieldGroup I

23-04-21 4

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)

≥10 dB

≥20 dB

Static threshold perimetry (Humphrey 24-2 or equivalent)

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

Reaction times were recorded from 20 stimuli over a 15 minutes drive.

Press buttons to respond

Results compared to

normative data

6 positions – rural road 1

6 positions – rural road 1

11 positions – city road 1

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

Strengths Weaknesses

Simulator based assessment - pros and cons

Strengths Weaknesses 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

Strengths Weaknesses 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

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

Force FeedbackSteering Wheel

VirtualCockpitDisplay

Shaker

SoundSystem

Rear- and Side-Mirror Displays

5 Gaze TrackingCameras

4 VideoCameras

Rexroth hexapod

X-Y Sled 2,3 * 2,5 m

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 examplesAlcohol (BAC - 0,2‰) fixed – should it be differentiated?Deafness OK to drive – why?Epilepsy – OK with medication and no seizure for 3 monthsDementia – 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

Useful field of view (UFOV) Dynamic Trail Making Test

• 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)

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

AgeMale

Female

Total

18-24 4 1 525-34 1 1 235-44 12 9 2145-54 22 5 2755-64 36 8 4465-74 63 2 65

75- 25 0 25Total 163 26 189

Age Num

Median distance km/week

18-24 5 40,025-34 2 202,535-44 21 250,045-54 27 300,055-64 44 200,065-74 65 200,0

75- 25 150,0Totalt 189 200,0

Most male, < 70% 55 +

Min 10000 km/yMax 25000 km/y

Diagnoses

Diagnosis, free Num %

% of those with a

diagnosis

Cumulative % of those with a diagnosis

Stroke 69 36,5 38,8 38,8Glaucoma 60 31,7 33,7 72,5Diabetes 21 11,1 11,8 84,3Eye injury 17 9,0 9,6 93,8Brain tumor 7 3,7 3,9 97,8Other 4 2,1 2,2 100,0Total 178 94,2 100,0  Missing 11 5,8Totalt 189 100,0

Select based on diagnosis and visual field defect

Difficult driving situations

Questions, comments?