Pendular pseudonystagmus.
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Eye Movements↗
Biomedical subjects
M G Nicolasen
Publications and source records attributed to M G Nicolasen.
Fitting adaptation models to velocity step responses: simulation of normal and abnormal responses.
A method is described to obtain suitable parameter values for an adaptation model that can be used to simulate velocity step (VS) responses. The input parameters are the dominant time constant fitted to the first part of the VS response and the time of reversal in nystagmus direction. This method allows a particular solution for the model previously defined by others with a vestibulo-ocular reflex (VOR) time constant, a time constant of adaptation, and a fixed (unitary) gain of the adaptation element. However, because it might be arbitrary to assume a unitary gain, we also studied a more general model with a variable gain element. It appeared that patients showing short responses had a short VOR time constant and less adaptation than normal. Patients exhibiting prolonged responses appeared to have an excessively long VOR time constant and more adaptation than normal, presumably to compensate for the long time constant.
Adaptation, Physiological↗
Cervico-ocular reflex enhancement in labyrinthine-defective and normal subjects.
The cervico-ocular reflex (COR) was elicited in 12 normal and 30 labyrinthine-defective (LD) subjects, lacking a vestibulo-ocular reflex (VOR) in the usual laboratory tests, by sinusoidal horizontal rotation of the body at 30 degrees amplitude and frequencies of 0.1, 0.2 and 0.4 Hz. The head was fixed in space and the eyes were open in total darkness. The gain of the COR was measured by relating the maximum slow phase velocity (MSPV) of the eyes to the maximum input velocity (19, 38 or 75 degrees/s) and by relating the cumulative eye displacement per hemicycle to the peak-to-peak amplitude of 60 degrees. The COR gain was below 0.25 in the normal subjects. In the LD subjects, a clear COR was observed with a gain of about 0.7 (SD 0.3) at 0.1 Hz, decreasing to about 0.4 (SD 0.2) at 0.4 Hz. There was no appreciable phase lag in 11 of the LD subjects. In 17 other LD subjects, the phase lag was close to 0 degrees at 0.1 Hz and increased to about 20-30 degrees at 0.4 Hz. Testing 4 additional normal subjects with the special instruction to attempt fixation of the knee during trunk rotation in the dark, resulted in an enhanced COR showing many "catch-up" saccades with a gain close to unity; the smooth component was also enhanced. The pattern with catch-up saccades was different from the pattern observed in most LD subjects, which closely resembled the normal VOR elicited by sinusoidal rotation. The special instruction to attempt fixation of the knee was also given to one LD subject during stimulation at 0.2 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
Short nystagmus duration of velocity step response as an indicator of labyrinthine defects.
The nystagmus response elicited by a velocity step of 90 degrees/s was evaluated in a group of 500 consecutive patients by computer analysis and by measuring the duration (t, in s) of the first phase of the response. A 90% log normal range of 37-55 s (mean 45 s) was established for t directly from the electronystagmogram (ENG) in a group of 12 normal subjects. The computer-based response type 'G-', i.e. 'Gesamtamplitude' (cumulative eye displacement), G less than 480 degrees, yielded a detection rate of labyrinthine defects (LDs) of about 65% with 35% false positives and 15% false negatives. A percentage of only about 25 of LDs was detected, with similar percentages of false detections, when using a criterion based on short t values. The lower yield was partly due to the fact that in some 35% of the cases t could not be measured; in the evaluable cases alone, the detection rate was 60% when using the G criterion and 50% when using the t criterion. It is recommended to measure G directly from the ENG, if t is too short or not available, whenever diminished vestibular responses are suspected.
Adult↗
Microcomputer programs for video stimulation of eye movements.
Programs have been developed for the Commodore 64/128, Amiga and BBC Acorn (Master) microcomputers to generate stimuli for eye movements on a television screen. The stimuli comprise eye movement calibration and the saccade, smooth pursuit and optokinetic tests.
Electronystagmography↗
Compensation of total loss of vestibulo-ocular reflex by enhanced optokinetic response.
The gain in the optokinetic nystagmus reflex (OKR) of 27 labyrinthine-defective patients was compared with that of 27 subjects without any otoneurological abnormality, who were matched by age and sex. The patients without labyrinth function exhibited significantly higher OKR gains than the control subjects, especially so at higher age. The observed enhancement of OKR gain in the absence of vestibular function is ascribed to the effect of optokinetic training brought about by enhanced slippage of retinal images due to lack of an efficient vestibulo-ocular reflex.
Adaptation, Physiological↗
The velocity step test. Its use in the evaluation of the effects of drugs in dizzy patients.
The effect of flunarizine (10 mg/day) was studied in open and double-blind clinical trials. Patients presenting the symptom of dizziness were diagnosed as having the hyperventilation syndrome. They showed vestibular hyperreactivity in the velocity step test. This test was performed before and after 4-6 weeks of treatment. The results of treatment were compared with a control or placebo group. In an open trial, 12 of 14 patients reported alleviation of dizziness during treatment and showed a significant decrease in right-left asymmetry of their velocity step responses. In a double-blind trial, no significant difference in effects or side effects was found between the drug and placebo groups.
Adolescent↗
Flunarizine treatment in dizzy patients with vestibular hyperreactivity and hyperventilation.
Flunarizine (10 mg/day) was given in an open pilot study to 14 patients with the primary complaint of dizziness, who showed vestibular hyperreactivity in the velocity step (VS) test and were proven to have a hyperventilation syndrome (HVS) without any other disease. The VS test was repeated after 4-6 weeks of treatment. Twelve of these HVS patients reported alleviation of dizziness. Objective evaluation of the results of treatment was attempted by defining suitable response parameters and comparing their values to those obtained in a control group of 14 healthy volunteers tested twice with the same interval. A significant decrease in right-left asymmetry in the VS responses of the patients on drug was found.
Adolescent↗
Diagnostic value of velocity-step responses.
For the nystagmic (after-)response in each direction it was evaluated in 618 patients whether the gain (initial velocity) and the time constant were normal, significantly low or high, thus constituting a specific 'response pattern'. In a number of diagnostic categories, 65% of the response patterns were 'typical', i.e., they were found in significantly high frequency. Symmetrical response patterns were predominant. Short time constant(s) and/or low gain values in either or both directions were found in labyrinthine defects. High gain values were found in otosclerosis after footplate surgery, in multiple sclerosis, hyperventilation syndrome, posterior fossa tumour and spasmodic torticollis. In those categories, except otosclerosis and posterior fossa tumour, also significantly high values of the time constant were found, as well as in the category of patients with exposed tympanic cavity and dizziness. A significant directional preponderance indicating the defective side was found for the low-frequency gain (i.e., the product of initial velocity and time constant) in 48% of the patients with unilateral canal paralysis. It is concluded that the velocity-step test is a powerful diagnostic tool in vestibular examination.
Brain Neoplasms↗
Correlation between velocity step and caloric response parameters.
The correlation between velocity step (VS) and caloric response parameters was studied in a series of several hundred patients who underwent a neuro-otological examination. The VS parameters initial velocity (V in degree/s), time constant (T in s) and Gesamtamplitude G ( = VT in deg) were all significantly correlated with the caloric response parameters. The highest correlation coefficients were associated with G.
Caloric Tests↗
Contralateral hyperactive caloric response in unilateral labyrinthine weakness.
In a series of 600 patients, 10 showed unilateral hyperactive caloric responses without a trivial explanation such as spontaneous nystagmus or directional preponderance. All 10 had unilateral weakness on the contralateral side, which was accompanied in 9 by cochlear hearing loss. It is assumed that the phenomenon of unilateral hyperreactivity in these cases can be explained by release from commissural inhibition on the basis of temporary vestibular decompensation.
Caloric Tests↗
Short vestibulo-ocular reflex time constants associated with oculomotor pathology in multiple sclerosis.
Significantly short vestibulo-ocular reflex (VOR) time constants were found in significant high numbers in patients with multiple sclerosis who had oculomotor dysfunction, especially when this dysfunction comprised both the smooth pursuit/optokinetic and the saccadic systems. Some time constants were in the range of 2.5-6 s, i.e. shorter than the presumed time constant of the primary afferent canal neuron. Increase in oculomotor impairment was accompanied by a decrease in time constants in some patients, whereas others showed a combined renormalization of previously disturbed oculomotor function and short time constants. Significantly high numbers of combinations of asymmetry in oculomotor dysfunction and a directional preponderance in time constant were observed, with the shorter time constant on the side of the (more severe) defect.
Electronystagmography↗