The effect of ocular fixation on the caloric nystagmus

[Dizziness and vertigo associated with vestibular neuronitis: the approaches to the diagnostics and treatment]

This article is focused on the peculiar features of diagnostics and treatment of dizziness and vertigo in the patients presenting with vestibular neuronitis. The authors present the detailed overview of various theories concerning etiology and pathogenesis of this condition, describe the methods for its clinical and instrumental diagnostics (including its differential diagnostics from other diseases associated with acute dizziness and vertigo). Special attention is given to the methods of pharmacological and physical rehabilitation of the patients suffering from vestibular neuronitis.

Jongkees' formula re-evaluated: order effects in the response to alternate binaural bithermal caloric stimulation using closed-loop irrigation

Normal limits for the response to caloric irrigation typically are specified as percentage of reduced vestibular response (RVR) and directional preponderance (DP). These measures are calculated using Jongkees' formula without regard to which ear is stimulated first. To assess the influence of the order in which the caloric stimuli are delivered we reviewed the responses to closed loop caloric irrigation of two groups of normal subjects and a group of unselected patients. Results indicated a consistent declining trend in response from the first caloric administration to the last administration in all groups and subgroups except in male patients over 60 years of age. Consequently, a significant bias in RVR was observed. Specifically, with the order of irrigation left cold, right cold, left warm, right warm, the mean percentage RVR for both the patients and control subjects was about a 5% right RVR. The bias resulted in right-sided unilateral hypofunction being diagnosed 2.4 times more often than left-sided hypofunction in patients aged 16-59. Our results differ from the previous literature that describes the effect of order on the response to caloric irrigation; this discrepancy may be related to our use of a closed-loop system for caloric irrigation. We conclude that vestibular laboratories should account for the effect of order in their patients' responses to caloric stimulation. We offer suggestions on how Jongkees' formula can be corrected for the effect of order.

Normal values in a routine ENG test

A total of 50 normal subjects were examined by electronystagmography for spontaneous and positional nystagmus. In this way the normal limit of the speed of the slow phase was determined to be 6.5 degrees/sec. By examining 15 of the subjects twice, the normal limit of the mean value of the two results was determined to be 4.5 degrees/sec. Forty-nine of the subjects were calorically tested, using 30 degrees and 44 degrees C stimulation. The results were calculated as indices expressing the degree of unilateral hypofunction and directional preponderance relative to the total caloric excitability. The results were evaluated for the duration of and for the maximum eye speed of the slow phase. The normal limits were determined as the mean value +/- twice the standard deviation. Our results indicate that a left-side hypofunction is a normal phenomenon and that duration and maximum eye speed of the slow phase reflect different aspects of the vestibular function.

Visual suppression of caloric nystagmus in normal individuals

The effects of opening of the eyes and of ocular fixation upon caloric nystagmus were investigated during the period of maximum intensity of caloric nystagmus in a series of 32 normal individuals. The percentage reduction in slow-phase velocity induced depended upon the test conditions, but, on the other hand, did not depend upon the temperature of the water applied as caloric stimulus. This latter fact favors the theory of visual suppression of the caloric test. Another striking finding was that a clear correlation definitely existed between the percentage reduction of suppression in slow-phase velocity and that in the multiplication product of amplitude by nystagmus frequency (P.A.F.) during the period of eye opening and ocular fixation. The percentage of suppression in slow-phase velocity is interchangeable with that in P.A.F., which broadens the practical scope of the routine test.