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Stockh 419(Suppl I):9–29
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a two-years prospective study with age, education and gender pair-matched patients. Acta
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22 Whiplash Effects on Brain: Voluntary Eye Movements
241
D.C. Alpini et al. (eds.), Whiplash Injuries,
DOI 10.1007/978-88-470-5486-8_23, © Springer-Verlag Italia 2014
23.1 Introduction
Different papers [ 1 – 5 ] suggest the existence of complex peripheral and, overall,
central alterations in the vestibular system as a consequence of a trauma in the cervical portion. Thus we studied optokinetic and visual vestibular system behavior in
subjects who previously underwent a cervical whiplash injury. The results of our
research could be both interesting from a clinical point of view and useful for medicolegal goals. Our methods could be suitable for pointing out alterations in central
sites as it is known that the nystagmus resulting from the contemporary optokinetic
and roto-acceleration stimulation with counterdirectional nystagmus is signifi cantly
weakened in brain stem and cerebellar lesions and more widely in the presence of
lesions in the posterior cranial fossa [ 6 – 9 ]. The visuo-vestibular interaction has not
yet been adopted in the study of cervical whiplash injury.
23.2 Methods
The investigation was carried out on 32 subjects of age between 21 and 48 (18 men
and 14 women) who had undergone a cervical trauma for a traffi c accident with
whiplash injury (Table 23.1 ). Thirteen subjects were examined within the third
month following the accident (1st group), six subjects between the third and the
sixth month (2nd group), and 13 subjects later than 6 months up to 24 months (3rd
group). It is important to note that we observed a spontaneous horizontal nystagmus
in three subjects (one for each group) with an incidence of 9.3 % out of the total.
The recording of ocular movements was done by the usual method using an
eight-channel Tonnies electronystagmograph. The subjects were sitting with their
heads still, on a Tonnies rotatory chair Pro model, which was placed in the middle
A. Salami (*) • M. C. Medicina • M. Dellepiane
Otorhinolaryngology, “San Martino” Hospital, Largo Rosanna Benzi 10, 16132 Genoa , Italy
e-mail:
http://www.otorinoangelosalami.com/contatti
2 3
Whiplash Effects on Brain: Optokinetic Nystagmus and Visuo-Vestibular Interaction
A. Salami , M. C. Medicina , and M. Dellepiane
242
of a rotatory cylindrical chamber with a diameter of 2 and 1.9 m high. Its white
internal area was covered with 32 black vertical contrasts (Fig. 23.1 ), each one
9.32 cm wide and with an angle of 5.61°.
The rotatory cylinder was lighted from above by a 100 W lamp and was driven
by a direct current engine able to reach the desired turning speed (clockwise and
counterclockwise of up to 2,000/s maximum speed, with preset acceleration ranging
from 1° to 20°/s2 ).
Table 23.1 Complaints after
cervical whiplash injuries
in 32 patients
Number
%
Headache 21 65.6
Subjective vertigo 13 40.6
Objective vertigo 4 12.5
Floating sensation 15 46.8
Tinnitus 14 43.7
Tinnitus and hearing impairment 5 15.6
Neck pain 13 40.6
Fig. 23.1 Rotatory
cylindrical chamber. The
Tonnies rotatory chair system
Pro in the middle
A. Salami et al.
243
Each patient was exposed to:
1. Postrotatory vestibular stimulation (VOR, vestibular ocular refl ex): with stop
test, eyes open in the dark at an angular velocity of 900/s which was subliminally
reached clockwise and counterclockwise.
2. Optokinetic stimulation (OKN, optokinetic nystagmus) “stare type” with a cyl-
inder rotation velocity of 300/s for 60 s with clockwise and counterclockwise
rotation.
The length of 60 s was chosen because we thought that VOR could sometimes
prevail over OKN. In this respect, our previous research on visuo-vestibular
interaction [ 10 ] had shown that in cases of lack of VOR substitution by OKN,
sometimes it took more than 20 s for the appearance of OKN.
3. Contemporary postrotatory vestibular and optokinetic stimulation (VVOR,
visuo-vestibular ocular refl ex) at the postrotatory stop: the light was turned on
and we effected optokinetic stimulation with a cylinder (and optical contrasts)
rotation capable of inducing an OKN which was beating on the opposite side of
the postrotatory vestibular nystagmus.
We took into account the fundamental parameter nystagmus “gain” as the ratio
between the angular velocity of nystagmus slow phase and the stimulation velocity.
VOR mean gain was calculated on the fi rst three beats; OKN mean gain was calculated on the beats in the fi rst 20 s; VVOR mean gain was calculated:
1. On the fi rst three beats during the fi rst 20 s of optokinetic stimulation, when the
resulting nystagmus was beating in the OKN direction.
2. Only on the fi rst three beats, when the resulting nystagmus was beating in the
VOR direction.
The results were compared with the ones we obtained in a group of seven normal
subjects, ages 28–36, and statistically evaluated (mean difference) by t -test.
23.3 Results
The results (Tables 23.2 and 23.3 and Figs. 23.2 , 23.3 , 23.4 , and 23.5 ) can be
summed up as follows:
• VOR: none of the normal or pathological subjects showed any signifi cant differences between the sides ( p > 0.05). In pathological subjects mean gain decreased
Table 23.2 Mean with standard deviation of the mean gain
VOR OKN
VVOR VVOR
OKN DIR a VOR DIR b
(3 beats) (20 s) (3 beats) (20 s) (3 beats)
Normal subjects 0.47 ± 0.08 0.46 ± 0.07 0.25 ± 0.09 0.32 ± 0.02 (−)
1st group (0–3 month) 0.34 ± 0.11 0.64 ± 0.18 0.15 ± 0.05 0.25 ± 0.08 0.12 ± 0.08
2nd group (3–6 month) 0.45 ± 0.12 0.73 ± 0.09 0.22 ± 0.14 0.29 ± 0.19 0.18 ± 0.13
3rd group (over 6 month) 0.38 ± 0.11 0.71 ± 0.11 0.28 ± 0.11 0.3 ± 0.10 0.18 ± 0.14
a
OKN DIR, nystagmus beating in the OKN direction
b
VOR DIR, nystagmus beating in the VOR direction
23 Whiplash Effects on Brain: Optokinetic Nystagmus and Visuo-Vestibular Interaction
244
in all three groups compared with normal ones (Table 23.2 ), but it was statisti-
cally signifi cant ( p < 0.05) only in the subjects of the fi rst group (Table 23.3 ), that
is, in those subjects who underwent the trauma more recently.
• OKN: none of the normal or pathological subjects showed any signifi cant differences between the sides ( p > 0.05). In pathological subjects mean gain increased—
with respect to normal ones—in all three groups (Table 23.2 ), with a signifi cant
increase ( p < 0.05) in the fi rst group and highly signifi cant increase ( p < 0.01) in
the second and third groups (Table 23.3 ).
• VVOR: in normal subjects VVOR always beats OKN direction, with a mean
gain on the fi rst three beats slightly inferior to the one calculated during the fi rst
20 s (Table 23.2 ).
In 16 cases the pathological subjects’ VVOR beats in the same direction of nor-
mal subjects (six in the fi rst, four in the second, six in the third group), with a mean
gain on the fi rst three beats which only in the fi rst group showed a statistically signifi cant variation (decrease) ( p < 0.01) compared with normal subjects (Table 23.3 ).
In the three groups of pathological subjects, the mean gain, during the fi rst 20 s,
showed a decrease compared to normal, but it was not statistically signifi cant
(Table 23.3 ).
In the remaining 16 cases (seven in the fi rst, two in the second, seven in the third
group), VVOR beats in the same direction as VOR for a variable length of 3–15 s
(Figs. 23.3 and 23.4 ) with a mean gain on the fi rst three beats always highly inferior
to VOR ones; VVOR beating in the VOR direction was followed by a variable
Table 23.3 Signifi cance test ( t -test) between normal subjects and whiplash patients
VOR ON VVOR OKN Direction
(3 beats) (20 s) (3 beats) (20 s)
Normal vs. 1st group
p < 0.05 p < 0.05 p < 0.01 p > 0.05
Normal vs. 2nd group
p > 0.05 p < 0.01 p > 0.05 p > 0.05
Normal vs. 3rd group
p > 0.05 p < 0.01 p > 0.05 p > 0.05
VOR VOR
VORVOR
OKN Stare OKN Stare
Fig. 23.2 Normal subject. From top to bottom : the postrotatory nystagmus (VOR) in the dark at
the constant angular velocity of 90°/s with clockwise and counterclockwise chair rotation; optokinetic nystagmus “stare type” ( OKN ) with the cylinder rotatory constant velocity of 30°/s for 60 s;
and visuo-vestibular ocular refl ex ( VVOR ) with a cylinder rotation which caused an OKN beating
on the opposite side of the postrotatory vestibular nystagmus. VVOR with counterdirectional VOR
and OKN always evokes a nystagmus beating in the OKN direction
A. Salami et al.
245
VOR
vVOR
vVOR
VOR
OKN
OKN
2 s
10
º
Fig. 23.3 Patient of the fi rst group. From top to bottom: postrotatory nystagmus (VOR) and optokinetic nystagmus “stare type” (OKN and visuo-vestibular ocular refl ex). Note increase of OKN;
VVOR is characterized by a nystagmus beating in the VOR direction for about 10 s. After a varying period of ocular immobility, a nystagmus beating in the OKN direction appeared. The vertical
arrows point out the chair stop. For further information, see Fig.
23.2
23 Whiplash Effects on Brain: Optokinetic Nystagmus and Visuo-Vestibular Interaction
246
period (a few seconds) of ocular immobility and then by a nystagmus beating in the
OKN direction (Fig. 23.5 ).
23.4 Discussion
The results of our research pointed to a statistically signifi cant decrease of VOR and
VVOR mean gains (beating in the OKN direction calculated on the fi rst three beats)
compared with normal subjects in the patients of the fi rst group and a signifi cant
VOR
VOR
OKN
OKN
VOR
VOR
2 s
10
º
Fig. 23.4 Patient of the second group
A. Salami et al.
247
increase of OKN mean gain in the patients of all the three groups. Furthermore, at
VVOR, immediately after the stop, we observed a nystagmus beating in the VOR
direction which lasted from 3 to 15 s in 16 patients out of 32 (seven in the fi rst, two
in the second, seven in the third group).
In 1968 and in 1970, Miura et al. [ 11 , 12 ] observed that cervical trauma of a
certain extent (about 7 G) which was experimentally induced in rabbits determined
either microcirculatory alterations of brain stem and the superior portion of the
spine or circulatory disturbances of the peripheral labyrinth. By analogy we can
VOR
VOR
VOR
VOR
OKN
OKN
2 s
10
º
Fig. 23.5 Patients of the third group
23 Whiplash Effects on Brain: Optokinetic Nystagmus and Visuo-Vestibular Interaction
248
assume that the signifi cant decrease of VOR mean gain that we observed in patients
with cervical whiplash injury belonging to the fi rst group could be due to labyrinthic
alterations subsequent to circulatory labyrinthic alterations.
The possibility of damage, also minor, to peripheral vestibular structures as a
direct consequence of cervical whiplash injury is also suggested by Chester [ 13 ]
and by Brandt [ 1 ], as well as on the basis of the experimental data of Schuknecht
and colleagues [ 14 ], who found a degeneration of Corti’s organ and secondary of
the pertaining acoustic fi bers; these data could be taken into account in trying to
explain, partially at least, the vestibular and audiological complaints (particularly
hearing loss and tinnitus) referred to by some of our patients (Table 23.1 ).
As to the signifi cant increase of OKN mean gain that we observed in all three
groups, our results agree with those obtained by other authors [ 15 ]. Therefore, tak-
ing into account the importance either of vestibular nuclei in the production of OKN
[45, 35] or of the pathway (even if it is not completely known) which is crossed by
optokinetic impulses at the subcortical site (tectum region and pontinus tegmen)
[ 16 , 17 ] and if we also consider that the cerebellar nodulus and fl occulus receive
visual and proprioceptive vestibular inputs [ 18 – 20 ], we may conclude that OKN
increase in cervical whiplash injury is determined by (a) pathological reactivity of
vestibular nuclei caused by cervical proprioceptors “overexcitation” [ 21 ]. The con-
nections of cervical proprioceptors with brainstem and particularly with vestibular
nuclei and reticular structure are already known [ 22 ], and (b) an altered microcircu-
lation of brain stem [ 23 ] and/or by a neurological-vascular friction which may cause
functional disorders of CNS and in particular of brain stem structures in cervical
whiplash injury [ 24 ].
As to VVOR, it is known that the optokinetic-vestibular interaction with coun-
terdirectional VOR and OKN evokes, in normal subjects, a nystagmus which is
always beating in the OKN direction, with a mean gain decrease in relation to OKN.
Our present results confi rm these data as a further demonstration that a periph-
eral labyrinthic excitation, evoked by any technique and even if it is intense, induces,
in normal subjects, a nystagmus which is always overcome by a contrasting OKN.
Nevertheless in six cases out of 13 patients belonging to the fi rst group, VVOR
appeared with a nystagmus beating in the OKN direction, but with a mean gain—on
the fi rst three beats—which was signifi cantly decreased compared with normal subjects. Finally in 16 out of 32 cases of the three groups (seven in the fi rst, two in the
second, and seven in the third group), VVOR was characterized by a nystagmus
beating in the VOR direction.
Numerous studies of animal anatomy and physiology showed the importance of
the cerebellar fl occulus in the working out of visual vestibular interaction [ 25 ] and
its infl uence on central velocity storage mechanism [ 26 – 28 ]. Therefore this struc-
ture is likely to be involved as a consequence of cervical whiplash injury, and an
alteration may occur in the transmission of inputs coming from the caudal portion
of inferior olive nucleus. We may also face an alteration of the fl occulus control
function on vestibular inputs, as Miles and Fuller [ 29 ] have already showed.
From a clinical point of view, these data confi rm the importance of ENG exami-
nation in cervical whiplash injury. The alterations of OKN (statistically signifi cant
A. Salami et al.
249
increase of mean gain in all three groups of patients) and of VVOR (nystagmus
beating VOR direction) show—without reference to its pathogenetical origin—the
presence of lesions, especially of central type and more specifi cally regarding brain
stem and cerebellum. It is evident that these results are interesting from a medicolegal point of view. Therefore we can repeat Oosterveld and colleagues’ words: “In
cases where legal medicine is involved, the outcome of an extensive nystagmographic examination can be of utmost importance both for the doctor and for the
patients.”
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23 Whiplash Effects on Brain: Optokinetic Nystagmus and Visuo-Vestibular Interaction