Motor vehicle accidents (MVA) are the most common causes of whiplash injuries. Difficulties with driving and changes in driving behavior are reported by subjects with chronic whiplash associated disorders (WAD). Proper eye and head coordination is required for driving tasks. Disturbances of eye and head coordination were found in these subjects with chronic WAD.
The objective of this pilot study is to evaluate eye, head and trunk coordination in subjects with chronic WAD due to MVA and healthy controls during a target-tracking task using a functionally oriented approach in the context of driving.
The subjects performed target tracking tasks that reproduced eye and head movements required while driving. Head and trunk motion was captured using a motion capture system and eye movement was captured with an eye-tracker. Response time, time to target, and eye, head, and trunk contribution of movement were measured.
Subjects with chronic WAD presented delayed response time and time to reach the targets with both eyes and head compared to the control group, and tended to compensate the lack of neck motion with increased eye motion.
This study shows indications of impairments of eye and head coordination in chronic WAD due to MVA when compared to healthy subjects. These alterations may have implications for driving safety.
Eye and head response time and time to reach the targets were delayed in chronic WAD.
Increased eye motion to compensate for limited neck motion was found in chronic WAD.
Indications of impairments of eye and head coordination in chronic WAD was found.
Alterations found in subjects with chronic WAD may impact their drive safety.
Motor vehicle accidents (MVA) are the most common causes of whiplash injuries ( ; ; ). Up to 60% of individuals with a whiplash injury develop chronic neck pain ( ; ; ; ). Difficulties with driving and changes in driving behavior such as increased trunk rotation to compensate for limited neck rotation are reported by subjects with chronic whiplash associated disorders (WAD) ( ; ). Changes in driving behavior can impact their ability to drive safely by increasing the time required to recognize traffic signs and the response time to react to potentially dangerous situations, which may increase their risk for subsequent accidents and re-injuries ( ).
Safe driving requires adequate physical, cognitive, and psychological functioning. These requirements include proper postural motor control such as eye and head coordination which is required for driving tasks including mirror check, blind lane monitoring, and road side traffic signs monitoring. Physical impairments in chronic WAD are related to driving difficulties and that includes pain, limited neck motion and fatigue ( ). Disturbances of the eye and head movement control and increased neck muscle activity was reported ( ; ) and is likely to contribute to their driving difficulty ( ; ). These disturbances affect head position, movement sense, vision, and postural stability ( ; ). In addition, these physical impairments reduce patients’ functional activities including driving, reading, walking and dressing ( ). These impairments are related to poor treatment outcomes contributing to disability and impacting normal participation in social activities.
It is unknown whether the coordination of eye, head, and trunk in subjects with chronic WAD are impaired and manifest during a target tracking task using a driving context approach. Therefore, the objective of this pilot study was to evaluate eye, head and trunk coordination in subjects with chronic WAD due to MVA against healthy controls during a target tracking task using a functionally oriented approach in the context of driving. The hypothesis of this study is that subjects with chronic WAD will present impaired eye, head and trunk coordination with altered motion and increased reaction and target reaching time compared to control subjects. This study will help with a prospective study on the evaluation of chronic WAD using a driving simulator and with the development of a driving simulator rehabilitation program for patients with chronic WAD. This can ultimately improve the patient’s overall quality of life and can facilitate early return to safe driving.
Fifteen healthy subjects (10 females and 5 males, mean age of 24.8 ± 1.9) and 5 subjects with chronic WAD (2 females and 3 males, mean age of 25.6 ± 4.9) participated in this cross-sectional pilot study. For the control group, subjects with no previous history of persistent neck pain, injury or visual problems were included. Subjects were not considered for either group if they had a previous history of injury other than the current WAD, head and neck surgery, systemic inflammatory or neurological disorders, previous vestibular or visual disorders, or inner ear damage.
Subjects with WAD were classified according to the Quebec Task Force classification of WAD ( ); subjects with Grade IV WAD (fracture or dislocation) were not eligible to participate. Three subjects were classified as having Grade I, and 2 were classified as having Grade II. According to the neck disability index, 1 subject with chronic WAD had no disability, 2 had mild disability, and 2 had moderate disability. Persisted neck pain in WAD subjects ranged between 2 and 6 out of 10 (median of 4 and IQR = 3–6) according to the visual analog scale.
All subjects were informed about the study, and a consent form was signed upon agreement to participate. This study was approved by the University Ethics Review Board (IRB Protocol # 13–0434). The feasibility of the method to evaluate and analyze synchronized data for eye, head, and trunk coordination during target tracking tasks in healthy subjects was previously published ( ).
Target tracking task
The subjects performed a target tracking task that reproduced eye and head movements required while driving (e.g. reading traffic signs, watching for pedestrians crossing, and/or incoming traffic at intersections). Three projection screens were positioned in a semicircle format for projection of the targets ( Fig. 1 ). The center screen was placed 1 m in front of the test chair, and the left and right screens positioned at 120° angles in relation to the center screen.
During the tasks, subjects were seated in a chair looking straight at a projected central target at eye level. The projected central target (0°) was instantaneously repositioned to a 40° or 70° position to the left or right at eye level. The target positions were selected based on common range of head movements required while driving. Subjects were instructed to change gaze from the center target to the new position as quickly as possible. The targets changed position every 2 s and maintained in each position for 2 s. The center target position was always projected after the target change to 40° and 70° in order to represent eye and head movements required while driving (gaze always goes back to center after a gaze change to look at traffic signs, for example) ( ).
Three different presentations were used to project the targets at 4 different positions. In each presentation, each target position was projected 3 times in a random order. Therefore, 9 trials for each target position were measured with a total of 36 target tracking measurements over the entire data collection for each subject. A rest period of 1 min was used between presentations.
The familiarization of the task was first performed prior to data collection by projecting all targets at the same time and asking subjects to look at all targets while seated. The chair was adjusted if needed so the targets were always projected at eye level.
Head and trunk position was captured using a computerized video motion capture system utilizing four infrared cameras recording at 240 samples per second using Oqus integrated hardware and Qualisys Track Manager software (Qualisys Inc.; Gothenburg, Sweden). The cameras were calibrated prior to subject arrival. A head gear with a cluster of 5 reference markers (Applied Science Laboratories, Bedford, MA, USA), and additional 7 markers (2 on each acromion, one on C7, 1 cluster of 3 references on spinous process of T3, and 3 attached to the chair) were used to capture kinematic data. The head gear with the markers on the acromion and C7 were used to measure head movements (head in relation to trunk). The T3 cluster and the markers on the chair were used to measure trunk movements (trunk in relation to chair).
A portable lightweight eye-tracker (Mobile Eye XG, Applied Science Laboratories, Bedford, MA, USA) was used to measure eye-movement data using an optical system consisting of an eye and a scene camera mounted on a pair of safety goggles. The scene camera captured the scene that the subject was looking at and the eye camera recorded the position of the eye using 3 light projections onto the pupil. The pupil-corneal reflection is used as the measurement principle and it converts the eye position to external point of gaze by overlaying crosshairs on a video of the scene being viewed by the subject ( Fig. 2 ). The system has an accuracy of 0.5° visual angle and a resolution of 0.1° visual angle. Mobile eye was calibrated by asking the subject to look at 9 different adhesive targets that were placed to the center screen at predetermined locations. Fig. 2 A shows subject set up with mobile-eye and head gear, and Fig. 2 B shows the eye-tracker scene camera showing subject’s gaze at a 40° target.