Quantitative measurement of saccade amplitude, duration, and velocity.

A method for rapid, accurate measurement of saccade amplitude, duration, and velocity (average and maximum) was developed as a functional test of the extraocular motor system. Recordings were made with a direct-current electro-oculographic system, and data analysis was performed on a laboratory digital computer. Saccade amplitude and duration were found to be linearly correlated in 25 normal subjects, with a mean slope of 2.7 msec per degree over a large amplitude range. In the same subjects, saccade amplitude and velocity (maximum or average) had a nonlinear relationship that was best fit by an exponential equation. The two constants of this equation adequately characterized the relationship between saccade amplitude and velocity and permitted rapid statistical comparison between normal and abnormal subjects.

The saccade velocity test.

Scatter plots showing the amplitude versus velocity (maximum and average) relationship of horizontal saccades in 25 normal subjects and four groups of patients were statistically compared. Three patients with "subclinical" medial longitudinal fasciculus syndromes had significant slowing of adducting saccades, and two of these patients had unsuspected slowing of abducting saccades (although to a lesser degree). Five patients with olivopontocerebellar degeneration and three patients with myotonic dystrophy had significant slowing of saccades in both directions. Five patients with surgically documented acoustic neuromas did not have significant slowing despite brain-stem compression in three. It is concluded that the saccade velocity test can be a useful clinical tool in addition to its potential in clinical research.

Impulsive and sinusoidal rotatory testing: a comparison with results of caloric testing.

The usefulness of rotatory testing (impulsive and sinusoidal) as an indicator of impaired horizontal semicircular canal function was evaluated in 63 patients with unilateral and bilateral decreased caloric responses. The rotatory stimuli were precisely controlled over a large magnitude range and EOG recorded nystagmus responses were quantified using digital analysis techniques. Rotatory testing was consistently abnormal in patients with complete unilateral caloric paralyses but was normal in over one-half of the patients with significant but less than complete unilateral caloric paralyses. The difference in maximum slow component velocity (SVMX) of induced nystagmus after the largest rotatory stimuli was the best indicator of unilateral impaired function. The patients with bilateral decreased caloric responses demonstrated three categories of rotatory response: 1. normal at all magnitudes of stimulation, 2. decreased but present after large magnitude stimuli, and 3. absent responses. It is concluded that although rotatory testing cannot replace caloric testing it can provide useful clinical information particularly in patients suspected of having bilateral vestibular disease.

Quantitative measurement of smooth pursuit eye movements.

Smooth pursuit eye movements were quantitatively assessed in 25 normal subjects and 22 patients. A laboratory digital computer was used to compute 200 eye velocity samples per second and to statistically compare these eye velocity measurements for five different object velocities. Of six statistics evaluated, mode eye velocity showed the least variability in normal subjects and was most frequently abnormal in patients. Compared to normal subjects, patients with brain stem degeneration and cerebellar-pontine angle tumors with brain stem compression had significant impairment of smooth pursuit. Patients with peripheral vestibular lesions and C-P angle tumors without brain stem compression did not have impaired smooth pursuit. These preliminary findings suggest that quantitative measurement of pursuit eye velocity can be a sensitive test for brain stem dysfunction.

Caloric testing. 3. Patients with peripheral and central vestibular lesions.

Results of bithermal caloric testing in 83 patients with unilateral peripheral vestibular disease, cerebellopontine angle tumors and vertebrobasilar insufficiency were compared in order to find which response measurements identified the most abnormal responses in each disease category. A laboratory digital computer was used to quantitatively assess each caloric response and a large digital computer was used to statistically compare 110 measurements generated from each caloric test. Of the commonly used response parameters maximum slow component velocity (SVMx) and sum of slow amplitudes (SSA) were most sensitive in each category and duration of response (TDUR) was least sensitive. This order was maintained for the vestibular paresis (VP), directional preponderance (DP) and temperature effect (TE) formulas. The magnitude of DP was significantly correlated with the magnitude of spontaneous vestibular nystagmus and both occurred with approximately the same frequency in peripheral and central disorders. There was no reliable way of separating end-organ from VIII nerve or peripheral from central disorders on the basis of the caloric responses.

Caloric testing 2. results in normal subjects.

A large number of variables were examined simultaneously for 43 normal subjects over the four irrigations of a caloric test. Care was used for every step of the testing procedure and data analysis to eliminate as much of the variance in the caloric responses as possible. The normality of each variable's distribution was examined using the Wilk-Shapiro W test and corrected if necessary by the best of several transformations. The means, standard deviation, and 95% confidence intervals of the resultant data were derived. Statistical tests of temperature, sidedness, and directionality were done on the variables and several important sources of variance were found and explained.

Caloric testing. 1. Effect of different conditions of ocular fixation.

Twelve normal subjects received standard caloric testing under the following conditions: 1) fixation, 2) Frenzel glasses in a dimly lit room, 3) eyes open in total darkness, and 4) eyes closed. Multiple nystagmus response parameters were evaluated and statistically compared for each condition. Fixation markedly diminished induced nystagmus and produced the largest coefficient of variation for each response parameter. Caloric testing with eyes closed resulted in periodic nystagmus suppression and a less distinct saw-toothed pattern. As with fixation, the coefficient of variation was consistently higher with eyes closed compared to eyes open in darkness or Frenzel glasses. It is concluded that caloric testing of the vestibulo-ocular reflex arc should be performed with eyes open in darkness or with Frenzel glasses.

Algorithm for the multi-parameter analysis of nystagmus using a digital computer.

A computer program for analyzing nystagmus has been developed and can be used on a small laboratory digital computer. The algorithm accepts digitized data and looks for the minimum and maximum (minmax) points of the nystagmus waveform. These points in turn are used to define seven descriptive parameters of nystagmus, including the amplitude, duration, and velocity of the slow and fast phases, and the frequency. The algorithm uses three user-adjusted criteria for accepting or rejecting minmax points. The treatment of noisy or irregular data can be improved by adjusting the values of these criteria.

A new method for determining impulsive time constants and their application to clinical data.

We have developed an accurate, convenient method for determining unique values of vestibular time constants from impulsive tests. The method was used to determine the mean values and standard deviations of 36 normal subjects. A comparison between these normal values and data from patients with cerebellopontine (CP) angle tumors or unilateral peripheral vestibular lesions showed no significant difference in the values of the time constants. We conclude that shape-descriptive parameters such as time constants cannot differentiate between subjects and patients.

Is the adaptation model a valid description of the vestibulo-ocular reflex?

The pendulum model of the vestibulo-ocular reflex, including the effects of adaptation, has been evaluated using the responses of 36 normal subjects to impulsive stimuli of 128 and 256 degree/s. Estimates of the model parameters such as the time constants, the slow velocity threshold, and the minimum stimulus required to produce an after-nystagmus have been obtained using a new analytical technique. Although some of the data support the validity of the adaptation model, evidence is presented to demonstrate that the overall applicability of the model is limited.

The impulsive test in man.

The impulsive test is brief and comfortable to the patient. The SVM is the best discriminator of the variables examined. By using percent differences between CW and CCW responses in the same subject at the same stimulus magnitude, we can define a range for the normal population and indicate patients outside that normal range. The impulsive test gives directional information in patients with unilateral lesions. In patients with severe bilateral loss of vestibular function, measurable responses are still obtainable; while in patients with primary cerebellar disease, responses are increased. The test may also be useful in giving anatomic information about posterior fossa lesions.