Methods considerations for nystagmography

Abstract

Objectives1. To assess the reproducibility of eye movement velocity measurement using two methods: traditional electro-oculography (EOG) and infrared video-oculography (VOG) and,2. Determine whether the normal values for unilateral weakness and bilateral reduction of caloric responses vary according to method employed.BackgroundVestibular testing frequently involves measurement of eye movements. EOG has been the standard method for decades, but VOG and other methods have recently become popular. The assumption has been that all methods measure eye movements equally and accurately but this assumption has not been validated. In this paper we examine this assumption.MethodsEye movements were recorded simultaneously with commercially available EOG and VOG methods to evaluate differences in results for nineteen normal subjects undergoing caloric tests with warm and cold water. Examination of the records permitted identification and simultaneous measurement of 840 nystagmus beats.ResultsEOG and VOG measurements were correlated but the correlation was not strong (Spearman rho = 0.529, p < 0.01). Eye velocities recorded by the VOG system were greater than that for the EOG system. The mean VOG/EOG ratio was 1.71. Normal values used at our centre were adjusted to accommodate the use of video technology to account for the differences in sensitivity between EOG and VOG methods.ConclusionThe traditional EOG-based normal value for bilateral reduction of caloric response, 30 degree per second (d/s) based on traditional EOG measurements should be revised to 50 d/s for modern VOG testing in our lab. Normal values for vestibular testing may need to be re-evaluated when new technology is introduced. Each lab should verify normal values for their own methods and equipment.

Vestibular System: Anatomy, Physiology, and Clinical Evaluation

“…These responses occur via tractus vestibulo-reticularis. They often lead to, combined with other vestibular responses, the development of various symptom complexes, including various forms of kinetosis, formerly called motion sickness (marine, air) [6,10,11].…”

“…It is necessary to stress that the head movements are the combined ones, i.e., they are accompanied with linear and angular acceleration within various planes and directions. Due to joint functioning of four otolith organs and six semicircular canals, it is possible to perceive complex movements in space [11,13,14].…”

“…BPPV may develop at any age, most often from 50 to 70 years, affecting women twice as often as men. It may develop after prolonged bed stay, particularly after craniocerebral traumas [11,14,16,17].…”

“…Long-term betahistine treatment is often prescribed to prevent attacks and reduce their manifestation. However, the causes of its occurrence have not been fully understood [11,12,18].…”

“…There are three stages of manifestation of vestibular dysfunction and three stages of development-compensation, subcompensation, and decompensation [6,11].…”