Infrared video oculography

By Marcello Cherchi, MD PhD

For patients

Here are answers to some of the most common questions about infrared video oculography.

What is this test? Infrared video oculography uses a special, small infrared camera embedded in a set of goggles, which records your eye movements during various positions and maneuvers.
What is this test looking for? This test looks for abnormalities in eye movements.
Is this test experimental or investigational? This test is approved by the Food and Drug Administration. It is neither experimental nor investigational.
What happens during this test? During this test the physician, audiologist or technician will have you put on a set of goggles (containing the small infrared camera or cameras), and will have you perform a number of tasks while they observe your eye movements.
Is this test uncomfortable? Usually this test is well-tolerated. Some patients with specific diseases (such as benign paroxysmal positional vertigo) may experience brief nausea during part of the test. Vomiting is very unusual.
How long does this test take? The test takes about 5 minutes.
Do I have to prepare for this test? The test will give better results if you are not wearing any eye makeup or artificial eye lashes.
Are there any special instructions for what to do after the test? There are no special instructions for what to do after this test.

For clinicians

Practical summary

Infrared video oculography is an essential part of a patient’s examination. It is relatively inexpensive and well-tolerated. It can usually be accomplished in about 5 minutes, and has significant diagnostic utility.

Introduction

In a vestibular clinic, instrumented oculography, usually in the form of infrared video oculography, is an essential tool.

History (how the test came to be developed)

As digital photography became progressively miniaturized (Hain 2007), it became possible to house infrared video cameras within goggles to record eye movements during examination. As different manufacturers entered this market and brought down the price of these devices, they became sufficiently affordable to be used in vestibular clinics by physicians and vestibular physical therapists.

Early versions of these cameras would directly visualize the eyes. Later models used the equivalent of a half-silvered mirror (that would reflect infrared light) so that the patient could see while the camera would still indirectly record the eye.

For many years we used monocular infrared video oculography. We eventually began using binocular infrared video oculography, and have gradually come to prefer it.

Types of spontaneous and elicited eye movements viewed well with infrared video oculography

We briefly review several specific techniques and maneuvers. Most of these we use regularly. A few are uncommon, and we do not use them routinely. Typically the infrared video oculography portion of a patient’s examination takes about 5 minutes.

Spontaneous nystagmus

Spontaneous nystagmus refers to eye movements that occur spontaneously (without provocative maneuvers) while the patient is seated upright, trying to stare straight ahead.

Spontaneous nystagmus is typically the first thing checked during infrared video oculography, and it is among the most valuable observations. If there is spontaneous nystagmus, then compare its behavior with vision available versus vision removed. The presence of spontaneous nystagmus can help identify several pathologies. Various forms of spontaneously occurring nystagmus include:

Upright positional testing

Some older literature refers to upright positional testing as “vertebral artery testing,” though its utility in diagnosing vertebral artery pathology is questionable, as we discuss elsewhere.

Although some literature reports upright positional testing as useful in evaluating for cervicogenic vertigo (CV), we rarely find it useful in that regard.

Gaze-evoked nystagmus (horizontal more useful than vertical)

Evaluating for horizontal gaze evoked nystagmus is probably most useful in identifying whether any horizontal spontaneous unidirectional horizontal nystagmus obeys Alexander’s law, suggesting unilaterally reduced vestibular function, such as in vestibular neuritis (VN).

Evaluating for vertical gaze evoked nystagmus is less useful. However, the finding of horizontal and vertical gaze evoked nystagmus (in which the direction of nystagmus is in the same direction as gaze) suggests a deficiency of gaze holding mechanisms, which localizes to the cerebellum. This is part of the HiNTs test, used in the evaluation of acute vestibular syndrome, typically for distinguishing a posterior fossa lesion (such as stroke) from vestibular neuritis (VN).

Centripetal nystagmus is an unusual form of gaze evoked nystagmus in which the fast phase of the nystagmus beats toward (rather than away from) the primary position of gaze.

Rebound nystagmus

The finding of rebound nystagmus suggests cerebellar pathology.

Saccades, horizontal and vertical

Assessing horizontal saccades can be useful in identifying:

  • Horizontal saccadic dysmetria, often found in cerebellar disorders.
  • Slow horizontal saccades, sometimes found in some parkinsonian disorders and some cerebellar disorders.
  • A binocular infrared oculography system makes it easier to detect internuclear ophthalmoplegia (which, if modest, might escape detection on face-to-face ocular motor examination) during horizontal saccades.

Testing vertical saccades can be useful in identifying:

  • Vertical saccadic dysmetria, often found in cerebellar disorders.
  • Slow vertical saccades, as can be seen in some parkinsonian disorders and some cerebellar disorders.

Smooth pursuit, horizontal and vertical.

A common disorder of smooth pursuit is saccadic breakdown, the most common cause of which is aging (which can diminish the gain of smooth pursuit).

Optokinetic nystagmus

Assessing horizontal optokinetic nystagmus can be useful in identifying deficits occurring in fast-phase disorders, such as progressive supranuclear palsy (PSP), in which there is “hang up” at end trajectory of horizontal optokinetic testing.

Assessing vertical optokinetic nystagmus is rarely useful, but may bring out convergence-retraction nystagmus, and has been reported as abnormal in mercury toxicity.

Head shaking nystagmus

The presence of head shaking nystagmus (HSN) suggests an asymmetry in vestibular tone, resulting from any pathology causing unilateral vestibular weakness, of which the most common etiology is vestibular neuritis (VN).

Hyperventilation-induced nystagmus

The presence of hyperventilation-induced nystagmus (HVIN) suggests a unilateral lesion that can become irritative (stimulatory), such as a vestibular schwannoma.

Vibration-induced nystagmus

The mechanism of vibration-induced nystagmus (VIN) is unclear, but it is generally thought to enhance an asymmetry in vestibular tone resulting from unilateral vestibular weakness, the most common cause of which is vestibular neuritis (VN).

Valsalva-induced nystagmus

Probably the main diagnostic utility of finding Valsalva induced nystagmus is in the diagnosis of third window phenomena, such as semicircular canal dehiscence (SCD) or temporal bone fracture.

Positional testing for BPPV (Dix-Hallpike, side-lying)

The most common positional techniques for eliciting nystagmus compatible with benign paroxysmal positional vertigo (BPPV) are the Dix-Hallpike maneuver (for diagnosing involvement of the vertical canals) and the side-lying position (for diagnosing involvement of the horizontal canals). Positional testing is usually well-tolerated, but in some patients with unusually severe benign paroxysmal positional vertigo (BPPV) it may induce nausea, and sometimes vomiting.

Summary

Infrared video oculography is an essential part of examination in otoneurology. We prefer a binocular setup (rather than a monocular one) when available. This is a relatively inexpensive technology that is non-invasive and low risk. It is generally well-tolerated by patients. An adequate series of eye movement observations can usually be accomplished in about 5 minutes, and has significant diagnostic utility.

References

Hain TC (2007) Head-shaking nystagmus and new technology. Neurology 68: 1333-4. doi: 10.1212/01.wnl.0000261902.31303.cf

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