Automatic electronystagmus analysis and documentation: recent advances in the study of vestibular, optokinetic and pursuit tracking function

Evaluation of subjectivity in the interpretation of videonystagmography

CONCLUSION

Subjectivity seems to play a definite role in the interpretation of the pendular test, but somewhat less for caloric testing, where pure visual analysis seems to be more reliable. Automated values provided by proof-tested software may be useful.

OBJECTIVES

In some centers, the interpretation of videonystagmography is still based on direct visual analysis of recorded tracings. Our study addresses the importance of subjectivity in the interpretation of videonystagmographic readings.

PATIENTS AND METHODS

Two experts (one junior and the other senior) were asked to interpret the same caloric and pendular tests on two different occasions, 3 months apart. Initial reading was performed without knowledge of the patient's history or the results of other neuro-otological tests. Three months later, interpretations were done with complete access to the patient's charts. The experts' answers were compared to the values provided by the computer software.

RESULTS

For the pendular test, inter-expert agreement was poor. With knowledge of the patient's history, the expert's interpretations tended to coincide with the software's calculations. For the caloric test, interpretation was less variable.

Clinical usefulness of the personal computer for equilibrium examinations

A personal computer (PC) system and its usefulness for equilibrium examinations is reported. The system was introduced into clinical routine practice for the following purposes: i) Reduction of test result measurement troubles in clinical practice, ii) Clearer observation of eye movements and body sway, iii) Quantitative analysis of nystagmus responses or body sway, iv) Easy introduction into clinical practice of new parameters or new tests, v) Programmable arrangement of stimulating devices, and vi) Effective storage of test data. Our PC system has been successful for these purposes and provided many useful options in equilibrium examinations. Although computer systems for equilibrium examination have not been popular due to high costs, the PC system, which can be obtained at a reasonable price, has become as powerful a device as the conventional small computer, and is expected to become a popular method for both research and routine clinical practice in the near future.

[Automatic analysis by computer of the visual suppression test of pendular rotatory vestibular nystagmus]

This study presents an automatic computerized analysis of the visual suppression test of vestibular nystagmus. Visual suppression is measured during rotatory nystagmus examination. The amplitude variations and the frequency of the nystagmus are computed in the dark and in the light. This allows the computer to furnish with the help of an algorithm the percentage of nystagmus suppressed by ocular fixation. The results of the computerized analysis are compared to a qualitative evaluation. A percentage of 70% and more indicates a normal suppression reflex and corresponds qualitatively to a total or subtotal visual suppression. A percentage smaller than 70% indicates a pathological reflex corresponding qualitatively to a partial, weak or absent visual suppression. The study is based on 149 examinations realised in 12 healthy subjects and 137 patients. The patients are classified into 4 groups: a) 59 patients with peripheral vestibular lesions (Ménière's diseases 21, vestibular neuronitis 15, cupulolithiasis 16, ototoxicity 7), b) 67 patients with central lesions of the cerebellum and the brainstem (multiple sclerosis 23, infratentorial tumors 14, vascular brainstem lesions 14, degenerative diseases of the central nervous system 16), c) 6 patients with supratentorial central lesions (hemispheric vascular lesions 4, supratentorial tumors 2), d) 5 patients with congenital nystagmus. All healthy subjects and all patients with peripheral vestibular lesions have a total or subtotal visual suppression corresponding to computed rates greater than 70% (mean: 86.7% and 83.1%). In cerebellar and brainstem lesions about half the patients (56.8%) present a partial, weak or absent visual suppression corresponding to computed rates inferior to 70% (mean: 52.7%). In supratentorial disorders the visual suppression is total or subtotal with computed rates superior to 70% (mean: 79.2%). By patients with congenital nystagmus the visual suppression is uniformly pathological with computed rates inferior to 70% (mean: 19.2%). The results of the visual suppression test are concordant with those of smooth pursuit in 92.6% of cases and with those of optokinetic nystagmus in 89.3% of cases. This study confirms that the visual suppression test is a useful examination to detect disorders of the cerebellum and brainstem.

The effect of age on the visuo- and vestibulo-ocular reflexes of elderly patients with vertigo

To evaluate the effect of age and vestibular deficit on the vestibulo-ocular and associated visual reflexes, rotating chair (VOR), eye tracking test (ETT) and optokinetic (OKN) responses were investigated using comparisons between three populations: young normals, vertiginous elderly patients, and age-matched normal elderly subjects. The gain of ETT and OKN responses were reduced for both elderly populations as compared to young normals, but less so for the vertiginous elderly. VOR gain was more significantly reduced in the vertiginous elderly, though VOR time constant was as reduced as for the normal elderly. These results indicate that visual inputs, even in the elderly, are probably employed to compensate for a vestibular deficit.

Documentation of the recovery course and deficit side localization of an acute unilateral vestibular deficit using four-quadrant diagrams of slow phase velocity

The horizontal vestibulo-ocular reflex was studied in normals and in patients with an acute or compensated unilateral peripheral vestibular deficit (PVD) in order to determine the efficacy of various response measures of deficit side and central compensation for high rotation velocities. The profiles of whole body rotation and the visual fixation period was chosen to yield slow phase velocity (SPV) profiles comparable with those obtained with caloric irrigation. The chair rotation direction producing the smaller amplitude of slow phase velocity measured over culmination period obtained with 40 s of 5 degrees/s2 constant acceleration to 200 degrees/s represented a lateralizing sign of all acute, and 85% of all compensated PVD cases.

Classification of peripheral and central (pontine infarction) vestibular deficits. Selection of a neuro-otological test battery using discriminant analysis

The results obtained from a complete neuro-otological test battery were examined statistically in order to select measurement variables which would optimally indicate significant differences between four groups: normal patients, patients with partially compensated unilateral peripheral vestibular deficit, patients with an acoustic neurinoma and patients with central (brainstem) vestibular deficit. A stepwise-discriminant analysis was performed on measurements of slow-phase velocity obtained from each test. The primary measurements selected to assign a subject optimally to one population were the canal paresis (CP) of the caloric test, the eye-tracking gain contralateral to the deficit for a 15 deg/s stimulus, the gain asymmetry for optokinetic nystagmus with a 30 deg/s stimulus, and the level of spontaneous nystagmus. The resulting classifications were 100% correct for normal and central deficit patients. However, the division between peripheral deficit and acoustic neurinoma patients overlapped causing about 30% false classifications of neurinoma patients: some 20% of the peripheral deficit patients were classified as normal. If the CP was not available the discriminant analysis substituted the rotating chair response for 5 deg/s2, in place of CP. This substitution caused a 10 to 20% decrease in classification accuracy.