Computer analysis for routine electronystagmography tests

Wallenberg's syndrome: neurotological classification

OBJECTIVES

Visually induced eye movements were investigated in 26 patients with Wallenberg's syndrome.

METHODS

Slow-phase optokinetic nystagmus (OKN) velocities, pursuit gains, and percentage fixation suppression (%FS) of caloric nystagmus were recorded by DC electrooculography (EOG), and stored directly onto FM magnetic tape.

RESULTS

OKN velocities, pursuit gains, and %FS decreased toward the lesion side (group A), whereas OKN velocities and pursuit gains decreased toward the side contralateral to the lesion side. %FS decreased toward the lesion side (group B). MR images in group A showed that lesions were only in and near to the vestibular nuclei, and images in group B showed that lesions extended to the cerebellum.

CONCLUSION

Visually guided eye movements allow classification of Wallenberg's syndrome into two types, one with brainstem lesions and one with both brainstem and cerebellar lesions. This demonstrates that assessing eye movements is helpful in supplementing MRI data.

Aging effects upon smooth pursuit induced by step-ramp stimulation

OBJECTIVE

in predictable target movements, pursuit gains are extremely close to 1.0. Under these conditions, aging effects upon pursuit have not been detected. Step-ramp stimuli produced by unpredictable combinations would be favorable procedures to assess the properties of smooth pursuit between young and aged people.

METHODS

the target was a 0.5 degrees red laser spot. Eye movements of 49 normal subjects (26 younger subjects less than 49 years old and 23 older subjects more than 50 years old) were recorded with infrared reflection oculography and sampled at 250 Hz. Step direction and distance (2, 4, 6, 8 degrees) followed by 10 degrees /s ramp speed movement in the same (onward stimulus) or opposite to the direction (backward stimulus) were programmed in an unpredictable way before each set of ten tests. Both onward and backward stimulation were randomly given for each subject.

RESULTS

in the onward study, there was a close correlation between retinal slip velocity (RSV) and eye acceleration (EA), which was expressed as a regression curve, being steeper in the younger group. This means that the younger subjects could produce faster velocity and greater acceleration than the aged group (P<0.05).

CONCLUSION

subtle reduction in visual acuity, visual fields and contrast sensitivity will be one of possible causes, and the degradation of cortical areas crucial for visual processing might be one of possible causes of slowing of pursuit EA.

The study of optokinetic 'look' nystagmus in children: our experience

Seventy health children underwent an OKN trial. The authors have chosen to perform only four tests (slow and fast clockwise and counterclockwise OKN) taking into account (in agreement with several international studies) four parameters: sTAP, fTAP, sTSAP, fTSAP (where s and f indicate the velocity of the shifting target slow or fast, TAP is total asymmetry percentage of the SSC--speed of slow components--and TSAP is total asymmetry percentage of saccades). They carried out the statistical analysis of the results, which did not show peculiar difference between child and adult OKN. The result of the test was independent of the side first tested and of sex. The authors have tried to identify the normal range of values more suitable to the study of child OKN; on the basis of the calculation of the 95% percentile the normality range was wider than the range assumed for adults. The authors have also tried to subdivided the results for three different groups of age (I = 3-7 years; II = 8-11 years; III = 12-14 years) in order to observe the degree of OKN maturation with age. From the results obtained the maturation of OKN pathways seems to occur in the 7th year of age for the slow movements; the findings related to the fast movements are more doubtful and need further analysis. Finally, although the number of saccades interposed to the tracings depends on enormous variations unrelated to age, sex and first side tested, our data show their higher incidence during the slow test.