Vestibular assessment has been clearly established as falling within the scope of audiologic practice, and educating future audiologists in vestibular diagnosis and treatment is now considered an integral part of all accredited educational programs.^1,2,3 However, a 2008 survey found that only 37 percent of respondents provided services of vestibular assessment, while only 11 percent reported providing vestibular rehabilitation.⁴

One reason could be confusion with terminology, in particular the terms oculomotor and electro- or video- nystagmography or oculography.

The importance of recording eye movements during vestibular testing has been described for many years.^5,6,7The terminology used for this battery of tests, however, can be problematic. Many sources across medical disciplines use the term oculomotor to describe the test battery and collective eye movements. Although oculomotor can be used to describe the overall movements of the eyes,⁸the diagnostic value of the test battery is minimized by using this term rather than ocular motor.

The eye movement test battery, including horizontal and vertical gaze, pursuit, optokinetics, and saccades, looks at the function of all six extraocular muscles, not merely those innervated by cranial nerve III, the oculomotor nerve and nucleus. Eye movements away from the midline (abduction) are controlled by the lateral rectus muscle and the abducens nerve (CN VI) and nucleus, while those downward and away from midline are controlled by the superior oblique and the trochlear nerve (CN IV) and nucleus.⁹In addition, some pathologies that audiologists may encounter during testing (e.g., CN VI palsy) have little to do with the extraocular muscles innervated by the oculomotor nerve. Therefore, the term ocular motor more properly describes what we do in the vestibular battery.

Another difficulty with the language is the interchangeable use of the terms nystagmography and oculography, in both the electrical and video formats (ENG/VNG versus EOG/VOG). Electro- and video-oculography refer to the recording of any eye movement with either electrodes or video techniques. Electro- and videonystagmography (ENG and VNG, respectively) are techniques to record nystagmus; a particular type of eye movement. Nystagmography is a type of oculography; but the reverse is not the case. Potentially even more confusing, however, is the common use of ENG/VNG to describe the caloric vestibular test, or the irrigation of the ear canals with either water or air stimuli. ENG/VNG allows for the recording of eye movements elicited by the caloric test. Vestibular function is assessed by evaluating nystagmus recorded through oculography techniques after stimulation of the vestibular system (e.g., calorics). The terms ENG/VNG and calorics are neither synonymous nor interchangeable.

Audiologists need to maintain the distinction between these and other terms used in vestibular testing. Increasingly, the medical identification and treatment of vestibular/balance disorders involves a number of professionals in a multi-disciplinary approach. By accurately and consistently describing tests and results, the audiologist can remain a significant contributor to the multi-disciplinary team that helps this patient population.

References

1. American Speech-Language-Hearing Association (ASHA). (2003). Scope of practice in Audiology. Retrieved Nov. 14, 2009, from www.asha.org/docs/html/SP2004-00192.html

2. American Academy of Audiology. (2004). Scope of Practice. Retrieved Nov.14, 2009, from www.audiology.org/resources/documentlibrary/Pages/ScopeofPractice.aspx

3. ASHA. (2006). Standards for Accreditation of Graduate Education Programs in Audiology and Speech-Language Pathology. Retrieved Nov. 14, 2009, from www.asha.org/NR/rdonlyres/686AF94D-5DA9-4D2C-96FB-2CA5E047527F/0/AccreditationStds0307.pdf#search="vestibular"

4. ASHA. (2008). 2008 Audiology Survey summary Report: Number and type of responses. Retrieved Nov.15, 2009 from www.asha.org/NR/rdonlyres/603E5591-88BC-4ACC-BFAA-7980F7AADAD8/0/08AudSurveyFrequencyReport.pdf#search="vestibular"

5. Barber, HO & Stockwell, CW. (1980). Manual of electronystagmography (2nd ed.). St. Louis: Mosby Publishing. Available through GN Otometrics.

6. Hain, TC. (1997). Background and techniques of ocular motility testing. In G. Jacobson, C. Newman, & J. Kartush (Eds.), Handbook of balance function testing. San Diego: Thomson Delmar Learning.

7. Shepard, NT & Schubert, M. (2008). Background and technique of ocular motility testing. In G. Jacobson & N. Shepard (Eds.), Balance function assessment and management. San Diego: Plural Publishing.

8. Oculomotor. (2006). In Mosby's dictionary of medicine, nursing & health professions (7th ed.). St. Louis: Mosby-Elsevier Publishing.

9. Leigh, RJ & Zee, DS. (2006). The neurology of eye movements. New York: Oxford University Press.

Jorge E. González, PhD, CCC-A, is assistant professor, Department of Audiology & Speech-Language Pathology, at Bloomsburg University of Pennsylvania in Bloomsburg, PA. Contact him at jgonzale@bloomu.edu.