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Localizing value of optokinetic afternystagmus
T C Hain1, S J Herdman, M Holliday
1Department of Neurology, Northwestern University School of Medicine, Chicago, Illinois.
The Annals of Otology, Rhinology, and Laryngology
|October 1, 1994
Summary
Optokinetic afternystagmus (OKAN) asymmetry can help identify unilateral vestibular lesions. After accounting for spontaneous nystagmus, OKAN parameters were reduced and showed directional asymmetry, indicating the lesion side.
Area of Science:
- Neuroscience
- Ophthalmology
- Vestibular System
Background:
- Unilateral peripheral vestibular lesions can cause asymmetric optokinetic afternystagmus (OKAN).
- Previous studies suggested OKAN's potential for lesion localization but overlooked spontaneous nystagmus.
- Assessing OKAN's utility in unilateral vestibular loss requires accounting for baseline nystagmus.
Purpose of the Study:
- To compare OKAN in patients with unilateral vestibular loss to healthy subjects.
- To evaluate the diagnostic value of OKAN parameters for localizing the side of peripheral vestibular lesions.
- To investigate the impact of spontaneous nystagmus on OKAN measurements.
Main Methods:
- Compared OKAN in 12 acoustic neuroma resection patients with unilateral vestibular loss to 30 healthy controls.
- Measured initial amplitude, time constant, and slow-phase cumulative eye position (SCEP) of OKAN.
- Calculated directional asymmetry and preponderance of OKAN parameters after offsetting for spontaneous nystagmus.
Main Results:
- Patients showed significantly reduced mean SCEP, initial amplitude, and time constant compared to controls.
- OKAN parameters exhibited directional asymmetry, being greater for stimulation towards the lesioned side.
- The SCEP parameter's directional preponderance demonstrated the highest sensitivity (58.3%) for identifying the lesion side.
Conclusions:
- OKAN parameters are significantly affected by unilateral peripheral vestibular loss.
- OKAN shows directional asymmetry favoring stimulation toward the lesion side.
- OKAN is moderately sensitive for unilateral peripheral vestibular loss and may be useful within a comprehensive diagnostic battery.