Zuccaro, TA, Fives, LA, Serna, CC; Program in Physical Therapy, State University of New York, Downstate Medical Center, Brooklyn, NY. Lori5s@aol.com.

BACKGROUND AND PURPOSE: The dynamic visual acuity test is used to evaluate the vestibulo-ocular reflex (VOR) component of vestibular function by assessing visual acuity during head rotation at frequencies at or above 1Hz. The test can be performed by passively rotating the subject’s head (pDVAT), or actively, where the subject performs self-generated head rotations (aDVAT). Research suggests nonvestibular mechanisms, such as efference copy, may improve performance on the aDVAT, thereby making the active test less sensitive to VOR dysfunction. The purpose of this study was to determine the role of predictability (efference copy) on VOR performance when horizontal head turning frequency and excursion were controlled. SUBJECTS: Twenty subjects (6 male, 14 female) ages 20-39 years, with no known vestibular or musculoskeletal impairments were tested. METHODS: Passive and active dynamic visual acuity and static visual acuity was assessed by determining the lowest line of legible optotypes on a Snellen chart placed 20 feet from each subject. For dynamic testing, head turning frequency was controlled by using an auditory metronome set at 1 Hz. and horizontal head turning excursion was limited to an arc of 60 degrees by a head mounted pointer and two rigid uprights fastened to the floor. ANALYSIS: The binomial test and the Wilcoxon Signed-Ranks Test were used to compare active and passive dynamic visual acuity. RESULTS: Discordant results of the binomial test found no significant difference between passive and active performance on the DVAT. Furthermore, concordant positive test results for active and passive scores were exactly the same within subjects. In addition, a Wilcoxon Signed-Ranks Test median score of zero suggested there was no strong evidence that the number of lines above static differed between active and passive conditions. CONCLUSION: These findings suggest prediction did not contribute to gaze stability during self-generated head rotation when head turning frequency and excursion were controlled. For the apprehensive patient or older adults with cervical degeneration, self-generated head rotation may be more appropriate than passive testing. In instances when self-generated head rotation is preferred, the aDVAT may be a viable alternative to the pDVAT if head turning frequency and excursion are controlled. The researchers designed a simple, inexpensive device to control head turning excursion, which can easily be constructed in the clinic. Further research is needed to determine the reliability and validity of the device used in this study. FUNDING SOURCE: None.

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