Interacoustics EyeSeeCam, Instructions For Use Manual

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EyeSeeCam vHIT Instructions for Use – EN Page 1
1 Introduction
1.1 About this manual
T
his manual is valid for the EyeSeeCam system (revsion 1.
2
). The product is manufactured by:
Interacoustics A/S
Audiometer Allé 1
5500 Middelfart
Denmark
Tel.: +45 6371 3555
Fax: +45 6371 3522
E-mail: info@interacoustics.com
It is the purpose of this manual to provide users of the Interacoustics EyeSeeCam module with all the
information required to carry out safe and reliable measurements.
In the past, a variety of techniques have been developed for measuring horizontal and vertical (that is,
two dimensional) eye movements. These include Electro-Oculography (EOG), Scleral Search Coil
(SCC) and photoelectric techniques. All of these techniques have been used in clinical and research
applications.
EOG, using surface electrodes is limited in its application by an accuracy factor of around 2 degrees.
It is further limited by its sensitivity to contamination by other electro-physiological artifacts and
electromagnetic sources in the environment. Signal drift impairs measurement of absolute eye position
and vertical eye position is highly non-linear. Photoelectric techniques have provided a higher degree
of accuracy than EOG (down to 0.25 degrees). However, these techniques are often limited only to the
measurement of the horizontal eye movement component.
Oculometric measurement with photoelectric techniques was first reported approximately fifty years
ago. These early experiments involved manual photographic techniques to measure horizontal and
vertical eye movement. Later, moving image techniques were employed to improve temporal
resolution of the recordings.
With the establishment of electronic techniques for image scanning and reproduction, the image
processing approach to oculometric measurement was introduced. With the development of the video
market, small, high-resolution FireWire and USB cameras have become available.
These systems enable an accurate (0.1 to 0.5 degrees), contact free recording of eye movements.
They can provide data on absolute eye position, and they are easy to handle.
Dizziness is a frequent symptom in ENT, Neurology, and General Medicine. Part of the clinical
examination of dizzy patients is based on the head impulse test (HIT) of the vestibulo-ocular reflex
(VOR). Head impulses are movements with small positional amplitude (10-2
0 degrees
) but high
acceleration (3.000-6.000
degrees
/s2) and high velocity (150-300
degrees
/s). When performed
clinically with no quantitative analysis, the test only detects the presence of a corrective saccade as an
indirect sign of a VOR deficit.
The HIT can easily be conducted at the bedside, but it has only a moderate sensitivity (63% in experts
and 72% in non-experts). Its specificity is 78% in experts and 64% in non-experts. Sensitivity,
however, can be improved to up to 100% when quantitative data of the VOR are obtained during the
head impulse. In patients with an acute unilateral vestibular deficit the quantitative HIT is as reliable as
the caloric irrigation test. Chronic patients, however, show a pathological caloric result in only 64% of
the cases but they were reliably identified by quantitative HIT. Hence, in the acute phase of a
vestibular deficit either of these tests is sufficient, but in the chronic phase, which is typical for a
vertigo and dizziness outpatient unit, the quantitative HIT is better.