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Smooth Pursuit Test

Written by Michelle Petrak, Ph.D.

 

What is the smooth pursuit test?

The smooth pursuit test is a test of the central vestibular system, assessing the patient’s ability to accurately track a visual target in a smooth, controlled manner.

Although several methods of smooth pursuit tracking have been researched, it is the controlled-velocity method that has been proven to be the most useful.

Thus, it is the controlled-velocity method that I will show in this guide.

 

How to instruct your patient

For the sake of convenience, I have provided a script below:

“You will see a green dot on the screen. The dot will move from one side of the screen to the other in a smooth, predictable motion. Your task is to follow the dot with your eyes while keeping your eyes precisely on the dot.  Try not to move your head and try not to get ‘ahead of’ or ‘behind’ the target.”

 

Normal smooth pursuit results

A patient with the ability to perform smooth pursuit tracking normally will produce a response in which the stimulus target and the eye tracings are almost identical (Figure 1).

Smooth pursuit summary screen, showing normal tracings, normal gain values, and normal symmetry values.

Figure 1: Smooth pursuit test showing a normal response to an increasing-frequency (Hz) target over time.

The stimulus is the yellow target line and the right and left eyes are the red and blue tracings.

The responses for each cycle of the pursuit are represented on the graph by red dots for the right eye and blue dots for the left eye.

Responses that are within threshold limits will fall in the white region and responses outside the threshold limits will fall in the grey shaded region.

 

Abnormal smooth pursuit results

It is important to know that the smooth pursuit test is the most sensitive of the ocular tests to age effects.

Thus, older patients are more likely to produce errors during the performance of the task.

Unlike saccades, where the movement of the eye is something that is unconsciously done many times throughout the day, the smooth pursuit test is something that may need to be ‘taught’ to the patient.

So, it is necessary to perform two or three ‘trials’ of the task to look for the patient’s best performance (unless the patient performs the task accurately on the first trial).

Figure 2 shows an example of an abnormal smooth pursuit test.

Smooth pursuit summary screen, showing saccades and abnormal gain values when the stimulus moves towards the right. Saccades preset as jumps rather than a smooth tracing. Abnormal gain values lie within a grey shaded area on the graph.

Figure 2: Abnormal smooth pursuit test showing reduced gains and saccadic intrusions in the higher frequencies with the patient having more difficulty when the target is moving towards the right.

Please note that it is possible that the patient can accurately track the target in one direction, but not in the other direction.

In most cases, the abnormality will present itself toward the side that has the lesion.    

 

Conclusion

Smooth pursuit tracking is an ocular test used to determine whether there is central pathology that is precluding accurate tracking of moving targets by the eyes.

Smooth pursuit tracking is susceptible to an age effect and may need the examiner to acclimate the patient to the task before recording.

 

Disclaimer

This is intended only as a guide; official diagnosis should be deferred to the patient’s physician.

 

About the author

Michelle Petrak, Ph.D.

Michelle Petrak, Ph.D., is the Director of Clinical Audiology and Vestibular Research for Interacoustics. Her primary role is development and clinical validation of new technologies in the vestibular and balance areas. She is a licensed private practice clinical audiologist at Northwest Speech and Hearing (NWSPH). Dr. Petrak received her doctorates in Electrophysiology (1992) and Biomolecular Electronics (1994) from Wayne State University and her Masters in Audiology in 1989. Her special areas of expertise include vestibular and balance assessments and management of the dizzy patient. Dr. Petrak is involved with new innovative product developments, clinical evaluations of new protocols, and publishing, teaching, and training on the management of patients with dizziness. She continues to lecture extensively nationally and internationally, and she has numerous articles published in the hearing industry journals. She also participates on the committees for several doctoral students as support for the research projects.

March 2017
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