Lucyna Schalén

Quantification of Tracking Eye Movements in Normal Subjects

Voluntary tracking eye movements were analysed in 20 normal subjects whose gaze was fixed on a visual target moving at six different constant velocities between 10 degrees s-1 and 60 degrees s-1. Tracking ability was quantified according to four parameters. The mean value and dispersion of each parameter at each velocity were determined. The maximum velocity gain of smooth pursuit was, on average, 0.98-0.75, gradually diminishing with increasing target velocities of 10-60 degrees s-1. Amplitude of smooth pursuit decreased gradually and was replaced by superimposed saccades at increasing target velocities. Saccades with amplitudes of 3-10 degrees were present at all target velocities, while those greater than 10 degrees occurred mostly at target velocities above 30 degrees s-1. Square waves were rare but equally frequent at all target velocities and seemed to occur randomly during tracking eye movements. An additional group of 9 subjects was investigated twice. Mean values of maximum velocity gain of amplitude of smooth pursuit and of frequency of superimposed saccades were higher on the second occasion, probably reflecting the effect of learning. Co-operation and interaction of the smooth pursuit and the saccadic subsystems to produce the voluntary tracking were discussed.

Velocity Patterns of Rapid Eye Movements

The peak velocities of saccades and fast phases of nystagmus were examined and compared in 20 healthy subjects. The peak velocities of both types of eye movements increased with increase of amplitudes. The saccades were found to be fastest in light, slower in darkness and slowest behind closed eyelids. The peak velocities of the quick phases of optokinetic and of vestibular nystagmus were found to be the same. Fast phases of optovestibular (optic as well as vestibular stimulation) nystagmus produced significantly higher peak velocities than the two others. At the same amplitude and during the same visual conditions the saccades were significantly faster than any type of fast components of nystagmus. The difference in velocity between voluntary and reflexive eye movements is possibly related to differences in antagonistic activity during these eye movements, but also to specific synaptic events during the voluntary action.

Effect of proprioceptor stimulation on postural stability in patients with peripheral or central vestibular lesion

Body sway in upright stance at rest and after inducing proprioceptor stimulation, elicited by vibration applied to the calf or neck muscles, was studied in 11 patients with peripheral lesion and in 17 patients with central vestibular lesion. The responses were compared with those of 20 normal subjects. Vibratory stimulus was applied at five different frequencies, ranging from 32 to 150 Hz, and at a constant amplitude of 2.1 mm. Postural stability was measured with a force platform in terms of average deviation of body position (ADBP) analyzed in relation to the individual maximum support distance in the anterio-posterior direction. In patients with peripheral vestibular lesion ADBP was moderately increased, compared to normal subjects, when the calf muscles were exposed to vibration under eyes closed conditions (i.e. no visual information available); stimulation of neck muscles both under eyes open and eyes closed conditions and stimulation of calf muscles with open eyes produced an ADBP of the same magnitude as in controls. In patients with central vestibular lesion, proprioceptor stimulation of calf and neck muscles caused increased ADBP whether with eyes open or closed. The ADBP induced by stimulation of neck muscles was significantly greater in patients with a central lesion than in those with a peripheral vestibular lesion. The results indicate that patients with peripheral lesion differ from those with central vestibular lesion in their reaction to proprioceptor stimulus; and that in patients with central vestibular lesion proprioceptor stimulation of the neck muscles produces disproportionately powerful cervico-collic reflexes.

Transdermally Administered Scopolamine vs. Dimenhydrinate: I. Effect on Nausea and Vertigo in Experimentally Induced Motion Sickness

The effect of transdermally administered scopolamine (TTS-scopolamine) (2.5 cm2 surface area, one and two patches) and dimenhydrinate (100 mg) on experimental motion sickness was examined in 16 healthy volunteers in a randomized double-blind study. Nausea was induced by Coriolis manoeuvre and vertigo by calorization of the ear. In all subjects, scopolamine was found in urine in concentrations indicating adequate absorption of the drug. One TTS-scopolamine, two TTS-scopolamine and dimenhydrinate caused a statistically significant reduction in nausea when compared with placebo. Dimenhydrinate was somewhat more effective against nausea than one TTS-scopolamine. Vertigo was significantly reduced after dimenhydrinate and two TTS-scopolamine. Side effects of both drugs were negligible, though gait disturbances and vertigo could occur occasionally after two TTS-scopolamine. No dose-response relationship was found between the urinary excretion of scopolamine and alleviation of nausea. Dimenhydrinate and TTS-scopolamine are both effective against motion sickness, the latter provided it is applied 6 to 8 hours before exposure to the stimulus causing the motion sickness.

Quantification of Tracking Eye Movements in Patients with Neurological Disorders

Tracking eye movements were studied in 20 healthy subjects and in 24 patients with vestibular neuronitis, disorders within the frontal cortex, the cerebellum or the brain stem. The tracking tests were performed at six different target velocities between 10-60 degrees s-1 and different parameters were evaluated. The maximum velocity gain of smooth pursuit as normal in the group with vestibular neuronitis but reduced in the groups with disorders within the frontal cortex, cerebellum and the brain stem. The total amplitude of tracking and amplitude of smooth pursuit were normal in the groups with vestibular neuronitis and frontal cortical disorders, while in the groups with cerebellar and brain stem disorders it was reduced. The frequency of superimposed saccades with amplitude range of 3-10 degrees was significantly increased in all groups; however, in the group with vestibular neuronitis the increase was significant only during tracking in the direction of spontaneous nystagmus. The number of superimposed saccades with amplitude range of 11-20 degrees was significantly increased only in the group with cerebellar disorders. The frequency of square waves was not significantly increased in any group. Quantitative analysis of tracking eye movements seems to be a valuable aid for evaluation of site of lesions in the central nervus system.

Inefficacy of penicillin V in acute laryngitis in adults. Evaluation from results of double-blind study.

Patients with acute laryngitis following an upper respiratory tract infection are often treated with antibiotics for their voice complaints, although, to our knowledge, the effect of such therapy has not been examined. In the present study, comprising 100 adults with laryngitis, the rate of resolution of vocal symptoms, as estimated from voice recordings or subjectively by the patients, was the same in patients who received penicillin V (pcV) as in those who received placebo. Similarly, the degree of rhinorrhea/nasal congestion and cough was not significantly influenced by pcV treatment. At the acute visit, nasopharyngeal cultures revealed Branhamella catarrhalis in 50%, Hemophilus influenzae in 15% and Streptococcus pneumoniae in 1% of the patients; the rate of elimination of these bacteria was the same in the pcV as in the placebo group. Thus, while suggesting that B catarrhalis and H influenzae are important for the pathogenesis of the disorder, our results do not provide support for the use of pcV in acute laryngitis.

Erythromycin in Acute Laryngitis in Adults

Moraxella catarrhalis and Hemophilus influenzae are isolated from the nasopharynx in 50% to 55% and 8% to 15%, respectively, of cases of acute laryngitis in adults. This finding indicates that these organisms, M catarrhalis in particular, are in some way involved in the pathogenesis of the disorder. In the present double-blind, placebo-controlled trial, the effect of erythromycin ethylsuccinate (0.5 g twice a day for 5 days) on the elimination of nasopharyngeal pathogens and reduction of clinical signs of upper respiratory tract infection, as well as on subjective complaints, was evaluated in 106 adults with acute laryngitis. The bacterial isolation rates at presentation were M catarrhalis 50%, H influenzae 18%, and Streptococcus pneumoniae 4%. In the 99 patients who completed the study, the elimination of M catarrhalis after 1 week was better in the erythromycin group (25 of 30 cases) than in the placebo group (6 of 19 cases; p ≤ .00038). The elimination of H influenzae was unaffected by erythromycin. Otolaryngologic examination did not reveal any significant group differences regarding laryngitis, pharyngitis, or rhinitis. Voice quality was improved after 1 week, irrespective of treatment. However, as compared to the placebo group, the erythromycin group reported fewer voice complaints after 1 week and fewer coughing complaints after 2 weeks. As acute laryngitis in adults is self-limiting, and subjective symptoms are spontaneously reduced after 1 week in most cases, antibiotic treatment does not seem warranted as a general policy. However, erythromycin may be justified in patients who are professionally dependent on voice function.

Pharmacological Treatment of Vertigo

A review of the treatment of vestibular disorders with drugs is presented. In animal experiments, administration of certain drugs, e.g. alcohol, barbiturates and chlorpromazine, retards the vestibular compensation, while others, e.g. caffeine, amphetamine and ACTH, accelerate the compensation. In compensated animals, some drugs produce overcompensation and some decompensation. A double-blind, randomized trial of the effect of scopolamine and dimenhydrinate in patients with vertigo of varying origin showed, as compared with placebo, that these drugs did not significantly alleviate the vestibular imbalance. The reason for the poor efficacy of the treatment may have been overcompensation of vestibular function loss and adverse effects caused by the drugs. Care should be taken that the drugs used do not retard the vestibular compensation caused by the central nervous system.

Detection of saccadic eye movements using a non-recursive adaptive digital filter

Saccadic eye movements provide important information about the neuron system at several levels. In recent years computer analysis of saccades has been adapted for use in clinical work. The most common detection methods do not always function without the users control and aid. In the present paper a digital filter is described for the detection of saccades. This non-recursive filter unscrambles saccade data which has been collected during the execution of an algorithm. The method is suitable for use with microcomputers. The filter is adaptive. Two concise experiments using the method are described.

Effect of Intravenous Diazepam and Thiopental on Voluntary Saccades and Pursuit Eye Movements

The effects of diazepam and thiopental on voluntary saccades and pursuit eye movements were tested in 9 volunteers, with an interval of at least 2 weeks between tests. One, 4 and 8 h after intravenous injection of diazepam (0.3 mg/kg) or thiopental (6.0 mg/kg), voluntary saccades and pursuit eye movements were tested and blood samples taken for analysis of drug concentration. As compared to results of tests without drugs, a significant reduction both of saccadic peak velocity and gain of pursuit eye movements was found 1 h after injection of either drug, but not after 4 and 8 h. The amplitude of saccades elicited with the 60 degrees stimulus was significantly reduced 1 h after injection of diazepam. Latency of saccades increased significantly up to 4 h after injection of either drug. No significant correlation was found between peak velocity of saccades and blood concentration of either thiopental or diazepam 1 h after administration. The present results confirm that in man saccades and pursuit eye movements are reduced by benzodiazepines and barbiturates, but provide no support for the previously described efficacy of saccades in monitoring the effect of benzodiazepines. It is hypothesized that diazepam and thiopental also induce reduction of voluntary saccades and pursuit eye movements via a general sedation of the central nervous system (CNS), besides having specific effects on CNS structures important to the performance of voluntary eye movements.