Computer-quantified positional nystagmus in normals.
BACKGROUND
Most current authorities agree that, in the absence of visual fixation, low intensity nystagmus can be recorded by electronystagmography (ENG) in clinically normal people. However, there are some notable dissenters, and the reported incidence, intensity, and direction of "normal" spontaneous/positional (S/P) nystagmus vary widely across laboratories. The highly subjective element introduced by manual interpretation of position test records compounds the problem of characterizing "normal" S/P nystagmus.


METHODS
A computerized ENG analysis system which removes this element of subjectivity is described, and results of a study validating its results against those of experienced ENG interpreters are reported.


RESULTS
The computer found an S/P nystagmus behind closed eyelids in at least one of five test positions in 42 of 51 clinically normal subjects (82.3%). This "normal" S/P nystagmus had a statistically significant overall directional bias toward left beating, but was affected by position--tending toward right beating in the left lateral position. The upper 95.4% confidence limits for computer-measured slow phase velocities of "normal" S/P nystagmus were -5.5 degrees/sec (left beating) and +4.4 degrees/sec (right beating).


CONCLUSIONS
Possible explanations for "normal" S/P nystagmus include clinically undetected pathology, normal asymmetries in the vestibulo-ocular reflex, and an imprinted oculomotor pattern such as might be created by reading.
Coats
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AC
Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, TX.
D000293:Adolescent; D000328:Adult; D000465:Algorithms; D003201:Computers; D004576:Electromyography; D004584:Electronystagmography; D005133:Eye Movements / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017120:Nystagmus, Optokinetic; D010865:Pilot Projects