Key Words
gain - head impulse - semicircular canal - vestibular - vestibulo-ocular reflex
INTRODUCTION
The video head impulse test (vHIT) is a relatively new tool used in vestibular clinics
to assess the function of all six semicircular canals (SCCs) ([Halmagyi et al, 2008]). A more diagnostic version of the bedside head impulse test first introduced by
[Halmagyi and Curthoys (1988)], the vHIT, provides objective measurement of the vestibulo-ocular reflex (VOR) through
lightweight goggles and a high-speed video-oculography system. With the advent of
the vHIT, information from each of the six SCCs, three from each ear, and their neural
pathways, may be obtained in a noninvasive manner. Eye movement is recorded with a
high-speed camera (250 Hz), and triaxial gyroscopes depict the angular movements of
the head to allow calculation of eye movement velocity in relation to head movement
velocity, also known as VOR gain. In addition, a monocular camera is able to record
any catch-up saccades that may occur during the head movement (covert saccades) or
after the head movement (overt saccades), which is indicative of peripheral hypofunction
([MacDougall et al, 2009]; [2013a],[b]).
In fact, the vHIT has proven to be useful in diagnosing peripheral hypofunction in
all vertical and horizontal SCCs in adults ([MacDougall et al, 2013a],[b]). MacDougall et al validated vHIT responses using the commercially available ICS
Impulse system by simultaneously collecting impulse data using scleral search coils
placed on the eyeball. These authors concluded that vHIT responses are equivalent
to the “gold standard” scleral search coil responses, but the vHIT is more comfortable
for the patient, less invasive, and more practical to use clinically ([MacDougall et al, 2013a],[b]).
Since publication of the validation studies, vHIT has been gaining acceptance as a
clinical tool to measure the function of the VOR in adults, and adult normative VOR
gain data for all six SCCs have been reported in several articles ([McGarvie et al, 2014]; [2015]; [Curthoys et al, 2016]). Using vHIT to assess SCC function in children is also gaining interest; however,
there are no studies assessing the normal VOR gain values of all six SCCs in children
aged <10 years. Because maturation can affect vestibular responses, including VOR
gain ([Valente, 2007]), it is important to determine if VOR gain changes throughout childhood using vHIT.
In addition, the use of adult normative vHIT data may not be appropriate for determining
vHIT normalcy in young children.
The reasons why vHIT would be beneficial for assessing the vestibular system of children
are clear. Presently, the standard pediatric test battery used to evaluate the vestibular
system includes rotational chair testing, videonystagmography, which culminates in
caloric irrigations, cervical vestibular-evoked myogenic potential, and ocular vestibular-evoked
myogenic potential testing. This current battery allows the clinician to primarily
assess the function of the horizontal SCCs and the otolith organs but does not offer
information about all the peripheral vestibular end organs. The function of the anterior
and posterior SCC, both critical components of the vestibular system, remains unknown.
Thus, even after spending a lengthy appointment time administering the current battery
of tests to a child, the clinician is left with less than a complete picture of the
peripheral vestibular system.
With the use of vHIT, clinicians are able to obtain information about the horizontal
SCCs without the use of lengthy, uncomfortable, and often frightening techniques.
Children would simply be required to wear goggles and maintain focus on a stationary
target, a non-invasive task many children may be more willing to perform. In addition,
information regarding the status of the anterior and posterior SCCs may be obtained
in a similar manner. According to published reports on adults ([Bartl et al, 2009]; [MacDougall et al, 2013a],[b]), vHIT can be completed in <15 minutes, allowing assessment of all six SCCs in a
brief time period. Although this brief assessment time would be desirable when testing
children, one recent study has reported that vHIT in children requires much more time,
taking approximately 20 minutes to complete just the lateral vHIT in children aged
3 to 16 years ([Hulse et al, 2015]).
The purpose of this study was to describe the normal vHIT response in a pediatric
population using a commercially available vHIT system (the ICS Impulse, GN Otometrics),
following the manufacturer’s specifications for testing. A healthy adult group was
also studied to verify testing technique and to make comparisons to the pediatric
data using the same examiners, equipment, and technique. The ICS impulse system was
selected because, to date, it is the only commercially available system that has been
validated against scleral search coils for all six SCCs. Additional aims of this investigation
were to determine what testing modifications are necessary to successfully perform
vHIT on children and determine the amount of time required to complete the test. The
ICS Impulse vHIT system was purchased for clinical use by Cincinnati Children’s Hospital
Medical Center in October 2014 and training and practice of the examiners took place
between October 2014 and February 2015. The data collection was completed at Cincinnati
Children’s Hospital Medical Center between February and March 2015.
METHODS
Participants
Thirty children, 4–12 years of age, with no history of vestibular dysfunction were
recruited for this study. Eleven healthy adults were also recruited to verify testing
technique and make comparisons with the pediatric normative data characteristics.
All participants were friends and/or family members of Cincinnati Children’s Hospital
employees. The 30 children were recruited into three age groups (4–6 years, 7–9 years,
and 10–12 years) to have a representative sample of ten participants in each age group
between 4 and 12 years. At the time of this investigation, the manufacturer did not
recommend testing children aged <4 years because of the lack of pediatric-sized goggles;
therefore, the youngest participants in this study were 4 years of age. Participant
characteristics can be found in [Table 1]. Normal vestibular function was assessed via a paper–pencil questionnaire related
to developmental milestones and balance and was completed by each participant, or
the participant’s parent, before testing (Appendix).
Table 1
Characteristics of the 41 Participants in This Study
|
Age (Years)
|
Mean (Years)
|
N = 41
|
|
Group I
|
4–6
|
5.6
|
10
|
|
Group II
|
7–9
|
8.7
|
10
|
|
Group III
|
10–12
|
11.4
|
10
|
|
Group IV
|
Adults (22–45)
|
34.4
|
11
|
Written informed consent was obtained from all adult participants and parents of minor
participants after the experimental procedure was explained. A child assent was obtained
from all children >10 years of age. The research protocol was approved by the Institutional
Review Board of Cincinnati Children’s Hospital Medical Center.
Procedure
All participants passed an immittance screening, using the Grason-Stadler GSI 37 tympanometer
(Eden Prairie, MN) to rule out the presence of middle ear dysfunction. vHIT measurements
were then recorded on all participants using the Otometrics ICS Impulse system (GN
Otometrics). The ICS Impulse vHIT system consists of a lightweight goggle with an
integrated high-speed camera (250 Hz) focused on the right eye and triaxial gyroscopes
enabling immediate recording of head and eye movements to assess VOR gain in all planes.
Participants were seated in a standard, fixed-height chair 1 m from a visual target
(1″ by 1″ sticker) on the wall at eye level. The ICS Impulse system goggles were placed
on the participant’s face and firmly secured with the attached elastic band provided
by the manufacturer around the back of the head to prevent goggle slippage and subsequent
inaccurate gain data. For the pediatric participants, a piece of 1″ thick foam, obtained
from a portion of the packing and shipping material found in a hearing aid box, was
placed inside the elastic band for additional security because of smaller head size.
In addition, a foot stool was used to keep the children seated upright and to help
stabilize the body during head movements. The pediatric test setup is shown in [Figure 1]. To ensure that the eye would be accurately tracked with head movements, the pupil
was aligned in the region of interest box and adjusted so the cross-hair was centered
on the pupil. To obtain optimal pupil recordings, the loose skin above the right eyelid
was pulled up and secured with the goggles.
Figure 1 Test set-up used in this investigation. The child is seated 1 m from the target (a
colorful sticker) on the wall, his feet are resting on a footstool and a foam pad
is secured inside the elastic band on the back of his head.
All testing was performed by three trained examiners, working in pairs (two with each
child). The three examiners were two clinical pediatric audiologists with >10 years’
experience each and one 4th year Au.D. student. Training consisted of hands-on instruction
and practice overseen by the manufacturer’s sales representative, completion of video
instruction provided on the manufacturer’s website, and through reading the directions
for testing in the provided instruction manual. In addition, each examiner continued
to practice the head thrust and recording procedure on colleagues and available family
members or staff over a 3-month period. For this investigation, two examiners were
present for every participant (the Au.D. student and one clinical audiologist). The
primary role of the clinical audiologist was to operate the equipment, whereas the
4th year Au.D student performed the head thrusts with the participant. Three adult
participants had one of the two clinical audiologists performing the impulses on them
because of lack of availability of the student when the participants were available.
Other than those three adults, the clinical audiologists did not perform impulses
on any other adult participants or on any of the pediatric participants, so as to
reduce inter-examiner variability.
Before the start of testing, calibration of the ICS Impulse goggles was performed
according to the manufacturer’s instructions outlined in the ICS Impulse reference
manual ([GN Otometrics, 2015]; Doc no. 7-50-1510-EN/00, pp. 23–25). Two red laser beams were emitted from the
goggles and projected onto the wall as two red dots 15° apart. Each participant was
instructed to move their head to place the red dots equidistant on the left and right
of the sticker and then watch the red dot as it jumped from left to right. The youngest
participants were instructed to count how many times the dot jumped from side to side
to ensure that the calibration dot was being watched. After calibration was accepted
by the system, calibration was manually verified by slowly rotating the participant’s
head to the left and right while the participant maintained focus on the sticker,
confirming that eye and head movement recordings were superimposed. All participants
were able to successfully achieve calibration and the default calibration was never
used.
After calibration, the participant was instructed to maintain focus on the visual
target or sticker. The participant’s head was rotated by the examiner using small,
rapid movements to the left and right to record the VOR response from the lateral
SCCs. Left anterior and right posterior (LARP) SCCs were tested with the head rotated
35°–45° to the right using rapid downward and upward head impulses. Right anterior
and left posterior (RALP) SCCs were tested with the head rotated 35°–45° to the left
using downward and upward head impulses. During testing, each pediatric participant
was asked to answer questions about the colorful sticker to ensure the child maintained
focus on the sticker. When attention began to deviate, a new sticker was used.
Head impulses in all conditions were manually delivered by the examiner with unpredictable
timing and direction until the gain values of 20 acceptable impulses were obtained
in each condition. According to the ICS Impulse reference manual (p. 28, 31, and appendix
2), the criteria required for the acceptance of a proper impulse included (a) a peak
head velocity of >100°/sec for lateral impulses; >50°/sec for LARP and RALP and (b)
the shape of the response matching the example shape on the testing screen of the
system. Test time was measured by the ICS Impulse system starting at the beginning
of each test (lateral, LARP, and RALP) until 20 acceptable impulses were collected
in each direction. Test time did not include calibration. All participants were permitted
to remove the goggles between tests for approximately 1–2 minutes, as needed, to reduce
the discomfort associated with wearing the goggles. Although the ICS Impulse instruction
manual states that movement of the goggles after calibration is “not recommended”
(ICS Impulse reference manual, p. 27), the examiners did not recalibrate after goggle
removal for any of the participants in this investigation as the patient file was
not exited and reentered at any time until all subtests were completed.
[Figure 2] shows an example of a vHIT hex plot obtained from an adult participant and a pediatric
participant. These results are representative of the type of vHIT responses obtained
in this study. Tracings containing extraneous eye movements not consistently occurring
were deemed as noisy or outliers and were eliminated. Results of each test were then
evaluated for the presence of saccades occurring during the head movement (covert)
or after the head movement (overt). Determination of the presence of a saccade included
a consistent spike in the response tracing occurring on >50% of impulses and having
a magnitude greater than half the size of the head movement. Although loosely based
on the recommendations of [Barin (2013)], this saccade criteria were purposely more conservative because the vHIT response
in children has not yet been characterized.
Figure 2 An example of a hex plot of an adult participant (left) and a pediatric participant
(right).
Data/Statistical Analysis
Head impulses were detected by the ICS Impulse system and were either accepted or
rejected based on an envelope around the expected head movement response, as well
as an acceptable peak head velocity. Mean VOR gains and standard deviations were calculated
for impulses in the lateral plane, as well as the LARP and RALP planes, and 95% confidence
levels were calculated for each age group. Data were analyzed using SigmaPlot 13.0.
Descriptive statistics, analysis of variance (ANOVA) and student t-tests were used to compare age groups and subtests of the vHIT battery. Nonparametric
tests (Kruskal–Wallis ANOVA and Dunn’s) were used if tests for normality (Shapiro–Wilk
and Brown–Forsyth) were not passed. Statistical significance was set at p < 0.05 for all comparisons. Post hoc comparisons were adjusted using the Holm–Bonferroni
method.
RESULTS
All 41 participants (100%) completed lateral head impulse testing. Forty of forty-one
participants (97%) completed LARP and RALP testing. One 4-year-old participant refused
to complete LARP and RALP testing because of discomfort of the goggles. For lateral
head impulse testing and LARP, data were removed from one participant in group 1 because
of excessive noise in the tracings, and one participant in group 2 because of goggle
slippage. For RALP testing, data were removed from one participant in group 2 because
of goggle slippage and one participant in group 4 because of excessive noise and eyelid
artifact. Peak head velocities of 100°/sec or greater for lateral impulses was achieved
for 95% of impulses across all participants and 50°/sec or greater peak head velocities
were achieved in 100% of both LARP and RALP impulses for all participants.
Test Time
[Table 2] shows the test time for each vHIT test across the different age groups. One-way
ANOVAs were run for each of the main subtests by age group to examine if time to complete
the subtest varied by age group. For Lateral test time, there was no overall difference
found (F = 2.535, p = 0.072). Likewise, for LARP, there was not a significant difference across age groups
(H = 0.298, p = 0.960) or for RALP (H = 5.474, p = 0.140). Significance may not have been met because of the small numbers of participants
in each group. Maximum total time (worst case scenario) to complete testing of all
SCCs was <15 minutes for all groups except the youngest (4- to 6-year-old) group,
where test time reached a maximum of 17 minutes. It should be noted that these test
times only include the time that the actual impulses were being administered and do
not include the time spent placing the goggles on the participant, calibrating, instructing
the participant, and allowing the participant to rest between tests. Therefore, these
test times underestimate the actual time spent with a participant completing all three
tests (lateral, LARP, and RALP).
Table 2
Mean (±SD) Test Time in Minutes for Each vHIT Subtest by Age Group
|
Age Group (Years)
|
Lateral
|
RALP
|
LARP
|
Maximum Total Test Time (Mean + 2SD)
|
|
4–6
|
2:00 ± 0:46
|
2:47 ± 1:40
|
3:23 ± 2:18
|
17:38
|
|
7–9
|
1:32 ± 0:22
|
1:32 ± 0:40
|
2:01 ± 0:47
|
8:43
|
|
10–12
|
1:18 ± 0:21
|
1:40 ± 0:43
|
2:02 ± 1:27
|
10:18
|
|
Adults
|
1:24 ± 0:30
|
1:26 ± 0:46
|
1:49 ± 1:00
|
9:10
|
Note: Maximum total test time includes the mean + 2SD of test time for each age group to
complete lateral, LARP, and RALP tests and does not include time used for patient
setup, calibration, breaks, or instruction. SD = standard deviation.
VOR Subtest Gain
Analysis of VOR gain for the six subtests for children and adults, as shown in [Figure 3], revealed that the mean RA amplitude was higher than the mean LA amplitude (T = 2.23, p = 0.014), the mean RP amplitude was lower than the mean LP amplitude (T = 3.07, p = 0.001), and the mean right lateral (RLat) amplitude was higher than the mean left
lateral (LLat) amplitude (T = 5.06, p < 0.001). In other words, RALP VOR gains were significantly higher than LARP VOR
gains for both children and adults.
Figure 3 Mean and standard deviation for each of the VOR gain subtests, for all children combined
and for adults.
VOR Gain by Age Analysis
[Figure 3] shows a comparison of the average VOR gain for all vHIT tests between the pediatric
and adult participants. As shown in the figure, pediatric gain was slightly more variable
than adult gain for each of the vHIT subtests, as shown in [Figure 3]. VOR gain for both adults and children were most variable for right anterior canal
stimulation. In addition, vertical canal stimulation produced lower VOR gain values
than lateral canal stimulation for the pediatric participants, with LARP gains noticeably
lower than RALP gains. One-way ANOVA revealed two subtests with significant overall
ANOVAs based on age group as the between variable. These were the LA subtest (F = 4.367, p = 0.011) and the LLat subtest (F = 3.103, p = 0.038). For LA, age group post hoc comparisons were significant for the adult group,
which had higher gain with the two youngest age groups (t = 3.103, p = 0.023 for 4- to 6-year-olds compared with adults and t = 3.052, p = 0.022 for 7- to 8-year-olds compared with adults) with Holm–Bonferroni adjustment
for multiple comparisons. For LLat, age group post hoc comparisons were borderline
significant for the adult group, which had slightly lower gain than the 7- to 8-year-old
age group (t = 2.819, p = 0.045) with Holm–Bonferroni adjustment for multiple comparisons. No significant
differences were found on overall ANOVAs for RA (F = 2.026, p = 0.129), RP (H = 4.680, p = 0.197), LP (F = 0.732, p = 0.540), or RLat (F = 2.459, p = 0.078). Because the age group analyses were mostly nonsignificant or of borderline
significance, normative data from Groups I to III were collapsed into one group of
30 pediatric participants aged 4–12 years, and are shown in [Table 3], compared with adults in the present study and adults for two previous studies.
Table 3
Mean ± Standard Deviation (5th, 95th Confidence Intervals) VOR Gain for Each SCC for
Pediatric and Adult Study Groups
|
Participants
|
Canal
|
Lateral
|
Anterior
|
Posterior
|
|
Ear
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
Children 4–12 years
|
Present study
|
0.96 ± 0.09 (0.79–1.14)
|
1.04 ± 0.09 (0.87–1.23)
|
0.80 + 0.11 (0.58–1.02)
|
0.90 ± 0.19 (0.53–1.27)
|
0.91 ± 0.14 (0.65–1.18)
|
0.83 ± 0.09 (0.65–1.01)
|
|
Adults
|
Present study
|
0.91 ± 0.06 (0.79–1.04)
|
1.03 ± 0.06 (0.91–1.14)
|
0.93 ± 0.07 (0.78–1.07)
|
0.95 ± 0.18 (0.60–1.30)
|
0.95 ± 0.09 (0.77–1.12)
|
0.89 ± 0.08 (0.73–1.05)
|
|
Adults
|
[Kidd et al (2014)]
|
0.98 + 0.10 (0.82–1.14)
|
1.04 + 0.11 (0.85–1.21)
|
|
|
|
|
|
Adults
|
[Curthoys et al (2016)]
|
0.92 + 0.06 (lower cutoff = 0.80)
|
1.00 + 0.07 (lower cutoff = 0.86)
|
0.96 +0.12 (lower cutoff = 0.71)
|
0.95 + 0.12 (lower cutoff = 0.70)
|
0.92 + 0.17 (lower cutoff = 0.58)
|
0.98 + 0.15 (lower cutoff = 0.68)
|
DISCUSSION
vHIT has previously been shown to be a useful tool in assessing the adult vestibular
end organ. Accurate vHIT evaluation in children depends on careful setup and administration
of the test, familiarity with what the normal vHIT response looks like, as well as
having established normative VOR gain data. This is the first study reporting normative
VOR gains and the normal characteristics of vHIT in children <10 years of age. Although
vHIT was able to be performed successfully on pediatric participants as young as 4
years in this study, RALP and LARP testing proved to be the most difficult to complete.
Some subject factors influencing the testing of the pediatric participants included
fine, slippery hair, small head and face size, and very large pupil size.
Direct observation during testing revealed a much larger pupil size in the pediatric
participants than the adults, which may have contributed to higher variability in
the vHIT responses in the pediatric participants. [Figure 4] shows the difference in pupil diameter between a 10-year-old and a 47-year-old.
It is well documented that children have larger pupil diameters than adults ([Birren et al, 1950]; [Jacobson, 2002]). Pupil diameter increases rapidly from 5 to 6 years, up to a maximum at 13–15 years
of age, and then slowly decreases into older adulthood, with major decreases beginning
at 40 years of age. The range of ages in our adult group was 22–45 years with a mean
of 34.4 years. Thus, the youngest members of the adult group also had somewhat large
pupil diameters, causing increased variability in VOR gain when testing the anterior
canals, particularly the right anterior canal. Initial attempts to constrict the pupil
through use of an otoscope light or a bright lamp shining close to the eye were unsuccessful
in achieving enough constriction in the pediatric participants to warrant their use.
Figure 4 Example of the difference in pupil diameter between a 47-year-old (top) and a 10-year-old
(bottom). These pictures were taken in the same room and lighting within minutes of
each other.
With the use of the ICS Impulse vHIT system, larger pupil diameter resulted in less
area to move the head during impulses while still allowing the entire pupil to be
visualized. Anterior canal impulses were most impacted by pupil size and eyelid artifact
was a problem that had to be overcome in many cases. During anterior canal testing,
a downward head impulse causes the eye to rotate upward. With a large pupil diameter,
this upward rotation of the eye often forces at least the top portion of the pupil
up into the eyelid. As the crosshairs maintain position in the center of the pupil
during testing, obfuscation of any part of the pupil, changing its shape, forces the
crosshairs to move and find a “new center” of the pupil. This causes a sharp deviation
of the crosshairs and a resulting dip in the response recording. In [Figure 5], the left image displays a tracing for right anterior (RA) stimulation, which includes
eyelid artifact, seen as the “V” in the peak of the movement. A normal tracing for
RA is displayed on the right. With a large pupil diameter and a small crosshairs and
tracking screen, more eyelid artifact was seen in the RA tracing of the pediatric
participant on the left. Impulse data from recordings containing a “V”-shaped dip
in the peak of the response must be eliminated from analysis as VOR gain calculation
will be inaccurate.
Figure 5 Example of a normal right anterior canal tracing (right) and a right anterior canal
tracing with eyelid artifact (left). See text for full description.
The adult mean VOR gain values calculated in this study are in agreement with those
previously published for all SCCs in adults. In addition, mean lateral SCC VOR gain
established for the pediatric group in this study closely agreed with the adult lateral
VOR gain in this study. With the exception of LA, which revealed lower VOR gain than
adults, and LLat, which revealed higher VOR gain for the 7- to 8-year-olds than adults,
there were no significant differences between the VOR gains of the pediatric and adult
participants on the vHIT subtests. VOR gain, however, appeared to be more variable
for LARP and RALP testing when compared with lateral testing.
Examining lateral testing across all participants, the RLat VOR gain was higher than
LLat VOR gain. This finding is consistent with previous normative data studies and
can be attributed to the recording of the right eye only using the ICS Impulse system
([Kidd et al, 2014]; [McGarvie et al, 2015]). It is known that the eye has a farther distance to travel in the skull during
adduction to maintain focus on a stationary target. Thus, monocular recording for
the right eye during an RLat impulse will result in greater VOR gain than that recorded
during an LLat impulse ([McGarvie et al, 2015]). In a similar way, and for the same reason, there is an asymmetry seen in the vertical
canal gains. The right (recorded) eye has farther to travel to maintain focus on a
target during RALP impulses versus LARP impulses, which results in higher gain values
for RALP. This asymmetry in vertical canal gains was most pronounced in the pediatric
group in this study. Furthermore, VOR gains for LARP and RALP were lower than VOR
gains recorded for lateral impulses in the pediatric participants. This finding is
consistent with those reported by [McGarvie et al (2015)] for all age groups studied. Thus, it appears necessary to adjust the VOR gain lower
cutoffs for LARP and RALP testing due to the normally lower gain recorded for these
tests.
During this study, several modifications were necessary to successfully complete the
testing with the pediatric participants. First, pieces of foam were added to the back
of the elastic band to prevent slippage of the goggles. The foam pieces aided in creating
a textured barrier between the smooth elastic band and the child’s hair. In addition,
the foam added bulk to the child’s head so that the elastic band would fit more tightly.
Presently, no pediatric-sized goggles exist for the ICS Impulse System. One of the
youngest participants in this study had a very small head size and, even with the
use of the foam pieces placed inside the elastic band on the back of the head, the
goggles had to be adjusted on the face to ensure that the camera was centered on the
right eye. This increased the amount of discomfort from the goggles and the 4-year-old
subsequently refused to continue the test after completing lateral vHIT because of
excessive discomfort. Allowing the participants to remove the goggles between tests,
while adding more time to the testing session, was deemed important by the examiners
to increase participant cooperation for the subsequent tests, as well as participant
retention. Because the VOR gain results achieved in this study for the adults and
the pediatric participants aged ≥10 years are in close agreement with those reported
in previous studies ([McGarvie et al, 2014]; [2015]), we feel that the effect of not recalibrating after goggle removal was inconsequential.
Attention span and the ability to focus on a target are other factors affecting the
successful administration of vHIT in children. The ICS Impulse system includes a blue
sticker that is to be placed on the wall for the participant to focus on during the
test. In this study, colorful stickers of familiar objects and characters were used
to keep the child’s attention focused on the area of interest. The children were asked
various questions about the sticker during impulse testing (How many sprinkles are
on the cupcake? What colors do you see? How many wheels are on the truck?), and when
attention began to deviate, a new sticker was placed on the wall. This method of keeping
the child’s attention worked well, but was challenging as the clinician operating
the computer was also responsible for quickly changing out stickers. Some children
required many sticker changes to stay focused, which no doubt increased the testing
time. It is presently unknown how a constantly changing target, such as a video played
on an iPod or smartphone would affect vHIT results or if it would increase extraneous
eye movements.
Keeping the child seated upright is imperative to delivering accurate impulses and
must be managed throughout the test as well. When moving a child’s head, if not anchored
to the chair or floor, the child’s body will also move and become unstable. This instability
can affect the clinician’s ability to present adequate impulses, which can increase
the test time. In this study, a foot stool was used to keep the children seated upright
and to help stabilize the body during head movements. Clinically, allowing a child
to sit with their legs crossed also provides adequate stability.
Finally, to obtain a good pupil recording, the skin just above the right eyelid was
pulled up and secured with the goggles. This effectively reduced eyelid artifact in
most of the participants. Without these modifications, testing the pediatric participants
would have been difficult. Further study is needed to determine the best means of
keeping children focused on a visual target to decrease test time and discomfort from
the tight-fitting goggles. Although the colorful stickers were a good alternative
to the manufacturer-provided sticker as a focal point for the pediatric participants,
it was still very challenging to keep the participant focused. Last, many of our pediatric
participants left the pediatric balance lab with red marks on their faces, particularly
on the sides of their noses. Pediatric-sized goggles would be a welcomed addition
to the ICS Impulse vHIT system.
Limitations of the study were that children <4 years were not included and only normal
participants were tested. Future studies with younger children, and those with vestibulopathy,
are needed to address these areas.
CONCLUSION
vHIT is a noninvasive test that can be used to successfully measure the function of
the lateral SCC in children as young as 4 years of age. Results indicate that adult
VOR normative gain values may be used when testing children with lateral vHIT. Lower
gain cutoffs should be used for LARP and RALP testing in children than the cutoffs
used for lateral vHIT. Care must be taken to obtain the most accurate measures and
reduce variability when testing children, particularly with LARP and RALP. Further
research is warranted to study LARP and RALP response reliability and validity in
children because of the highly variable VOR gains found in this population. Pediatric
modifications for vHIT testing are necessary to reduce goggle slippage and body movement,
as well as to increase attention and focus on the target. In addition, care must be
taken to ensure clear visualization of the entire pupil during testing by pulling
the loose skin above the right (recorded) eyelid up and securing it with the goggles,
effectively opening the eye wider. The time needed to perform vHIT in children can
range from just <10 minutes to >17 minutes, with younger children requiring more time.
If test setup, calibration, instruction, and breaks between tests are included, the
time needed to assess pediatric patients with vHIT could range from 15 minutes to
well >20 minutes, realistically. Studies looking at ways to reduce test time, without
sacrificing response accuracy, are presently underway.
Abbreviations
ANOVA:
analysis of variance
LARP :
left anterior and right posterior
LLat:
left lateral
RALP:
right anterior and left posterior
RLat:
right lateral
SCC:
semicircular canal
vHIT:
video head impulse test
VOR:
vestibulo-ocular reflex
APPENDIX: BALANCE HISTORY
APPENDIX: BALANCE HISTORY
Name of child: ___________________________
DOB: ____________________________________
Sex: ___________________
Who filled in this questionnaire: _________________________
At what age did your child learn to walk? ________________________
Has your child ever had an episode of any of the following (please check the corresponding
yes/no box):
|
Yes
|
No
|
|
1
|
Vertigo (the room/or your child feels like they are spinning)
|
☐
|
☐
|
|
2
|
Poor balance/clumsiness
|
☐
|
☐
|
|
3
|
Frequent falls
|
☐
|
☐
|
|
4
|
Brief episodes of inability to walk
|
☐
|
☐
|
|
5
|
Fear or panic without any obvious cause
|
☐
|
☐
|
|
6
|
Rapid back and forth eye movement (nystagmus)
|
☐
|
☐
|
