Browsing by Author "Schubert, Michael C."
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Item Cervico-Ocular Reflex in Normal Subjects and Patients with Unilateral Vestibular Hypofunction(Otology & Neurotology, 1/1/2004) Schubert, Michael C.; Das, Vallabh E.; Tusa, Ronald J.; Herdman, Susan J.Objective: To determine whether the cervico-ocular reflex contributes to gaze stability in patients with unilateral vestibular hypofunction. Study Design: Prospective study. Setting: Tertiary referral center. Patients: Patients with unilateral vestibular hypofunction (n = 3) before and after vestibular rehabilitation and healthy subjects (n = 7). Interventions: Vestibular rehabilitation. Main Outcome Measures: We measured the cervico-ocular reflex in patients with unilateral vestibular hypofunction before and after vestibular rehabilitation and in healthy subjects. To measure the cervico-ocular reflex, we recorded eye movements with a scleral search coil while the trunk moved at 0.3, 1.0, and 1.5 Hz beneath a stabilized head. To determine whether the head was truly stabilized, we measured head movement using a search coil. Results: We found no evidence of cervico-ocular reflex in any of the seven healthy subjects or in two of the patients with unilateral vestibular hypofunction. In one patient with chronic unilateral vestibular hypofunction, the cervico-ocular reflex was present before vestibular rehabilitation only for leftward trunk rotation (relative head rotation toward the intact side). After 5 weeks of placebo exercises, there was no change in the cervico-ocular reflex. After an additional 5 weeks that included vestibular exercises, cervico-ocular reflex gain for leftward trunk rotation had increased threefold. In addition, there was now evidence of a cervico-ocular reflex for rightward trunk rotation, potentially compensating for the vestibular deficit. Conclusion: The cervico-ocular reflex appears to be a highly inconsistent mechanism. The change of the cervico-ocular reflex in one patient after vestibular exercises suggests that the cervico-ocular reflex may be adaptable in some patients.Item Oculomotor Strategies and Their Effect on Reducing Gaze Position Error(Otology & Neurotology, 2/1/2010) Schubert, Michael C.; Hall, Courtney D.; Das, Vallabh E.; Tusa, Ronald J.; Herdman, Susan J.Objective: Vestibular adaptation exercises have been shown to improve gaze stability during active head rotation in individuals with vestibular hypofunction. Little is known, however, of the types of eye movements used during passive head rotation and their effect on gaze stability in individuals with vestibular hypofunction. The primary purpose of this study was to determine differences in oculomotor strategies and their effect on stabilizing gaze during ipsilesional passive and active head rotations in vestibular hypofunction. Patients: Subjects with unilateral (n = 4) and bilateral (n = 3) vestibular hypofunction and healthy subjects (n = 4) based on bithermal caloric and rotational chair testing. Intervention: Diagnostic. Main Outcome Measure: Head and eye velocity and position data measured with scleral search coil. Results: Subjects with unilateral and bilateral vestibular hypofunction generated 3 types of gaze-stabilizing eye movements with ipsilesional head impulses: slow vestibular ocular reflex, compensatory, and corrective saccades. The types of eye movements generated during active and passive head impulses were highly individualized. Gaze position error was reduced when compensatory saccades were recruited as part of the gaze-stabilizing strategy. Conclusion: Rehabilitation for individuals with vestibular hypofunction should identify individuals' unique gaze stability preferences and attempt to facilitate compensatory saccades.Item Recovery of Dynamic Visual Acuity in Bilateral Vestibular Hypofunction(Archives of Otolaryngology Head and Neck Surgery, 4/1/2007) Herdman, Susan J.; Hall, Courtney D.; Schubert, Michael C.; Das, Vallabh E.; Tusa, Ronald J.Objective: To determine the effect of vestibular exercises on the recovery of visual acuity during head movement in patients with bilateral vestibular hypofunction (BVH). Design: Prospective, randomized, double-blinded study. Setting: Outpatient clinic, academic setting. Patients: Thirteen patients with BVH, aged 47 to 73 years. Intervention: One group (8 patients) performed vestibular exercises designed to enhance remaining vestibular function, and the other (5 patients) performed placebo exercises. Main: Outcome Measures Measurements of dynamic visual acuity (DVA) during predictable head movements using a computerized test; measurement of intensity of oscillopsia using a visual analog scale. Results: As a group, patients who performed vestibular exercises showed a significant improvement in DVA (P = .001), whereas those performing placebo exercises did not (P = .07). Only type of exercise (ie, vestibular vs placebo) was significantly correlated with change in DVA. Other factors examined, including age, time from onset, initial DVA, and complaints of oscillopsia and disequilibrium, were not significantly correlated with change in DVA. Change in oscillopsia did not correlate with change in DVA. Conclusions: Use of vestibular exercises is the main factor involved in recovery of DVA in patients with BVH. We theorize that exercises may foster the use of centrally programmed eye movements that could substitute for the vestibulo-ocular reflex. Trial Registration: clinicaltrials.gov Identifier: NCT00411216Item Recovery of Dynamic Visual Acuity in Unilateral Vestibular Hypofunction(Archives of Otolaryngology Head and Neck Surgery, 8/1/2003) Herdman, Susan J.; Schubert, Michael C.; Das, Vallabh E.Objective: To determine the effect of vestibular exercises on the recovery of visual acuity during head movement in patients with unilateral vestibular hypofunction. Study Design: Prospective, randomized, double-blind study. Setting: Ambulatory referral center. Patients: Twenty-one patients with unilateral vestibular hypofunction, aged 20 to 86 years. Intervention: One group (13 patients) performed vestibular exercises designed to enhance the vestibulo-ocular reflex, and the other group (8 patients) performed placebo exercises. The placebo group was switched to vestibular exercises after 4 weeks. Outcome Measures: Measurements of dynamic visual acuity (DVA) during predictable (DVA-predictable) and unpredictable (DVA-unpredictable) head movements by means of a computerized test and measurement of intensity of oscillopsia by means of a visual analog scale. Results: As a group, patients who performed vestibular exercises showed a significant improvement in DVA-predictable (P<.001) and DVA-unpredictable (P<.001), while those performing placebo exercises did not (P = .07). On the basis of stepwise regression analysis, the leading factor contributing to improvement was vestibular exercises. This reached significance for DVA-predictable (P = .009) but not DVA-unpredictable (P = .11). Other factors examined included age, time from onset, initial DVA, oscillopsia, and duration of treatment. Changes in oscillopsia did not correlate with DVA-predictable or DVA-unpredictable. Conclusions: Use of vestibular exercises is the main factor involved in recovery of DVA-predictable and DVA-unpredictable in patients with unilateral vestibular hypofunction. Exercises may foster the use of centrally programmed eye movements that could substitute for the vestibulo-ocular reflex. The DVA-predictable would benefit more from this than would DVA-unpredictable.