Determination of smooth pursuit eye movement velocity in humans by computer

Anticholinergic activity in the nervous system: Consequences for visuomotor function

Acetylcholine is present in the peripheral and central nervous system, where it is involved in a number of fundamental physiological and biochemical processes. In particular, interaction with muscarinic receptors can cause adverse effects such as dry mouth, drowsiness, mydriasis and cognitive dysfunction. Despite the knowledge that exists regarding these common side-effects, little is known about how anticholinergic medications influence central motor processes and fine motor control in healthy individuals. This paper reviews critical visuomotor processes that operate in healthy individuals, and how controlling these motor processes are influenced by medications that interfere with central cholinergic neurotransmission. An overview of receptor function and neurotransmitter interaction following the ingestion or administration of anticholinergics is provided, before exploring how visuomotor performance is affected by anticholinergic medications. In particular, this review will focus on the effects that anticholinergic medications have on fixation stability, saccadic eye movements, smooth pursuit eye movements, and general pupil dynamics.

Eye movement recordings to investigate a supranuclear component in chronic progressive external ophthalmoplegia: a cross-sectional study

BACKGROUND

It has been postulated that eye movement disorders in chronic progressive external ophthalmoplegia (CPEO) have a neurological as well as a myopathic component to them.

AIM

To investigate whether there is a supranuclear component to eye movement disorders in CPEO using eye movement recordings.

METHODS

Saccade and smooth pursuit (SP) characteristics together with vestibulo-ocular reflex (VOR) gain and VOR suppression (VORS) gain in 18 patients with CPEO and 34 normal patients were measured using Eyelink II video-oculography.

RESULTS

The asymptotic values of the peak velocity main sequence curves were reduced in the CPEO group compared to those of normal patients, with a mean of 161 degrees/s (95% CI 126 degrees/s to 197 degrees/s) compared with 453 degrees/s (95% CI 430 to 475 degrees/s), respectively. Saccadic latency was longer in CPEO (263 ms; 95% CI 250 to 278), compared to controls (185 ms; 95% CI 181 to 189). Smooth pursuit and VOR gains were impaired in CPEO, although this could be explained by non-supranuclear causes. VORS gain was identical in the two groups.

CONCLUSIONS

This study does not support a supranuclear component to the ophthalmoplegia of CPEO, although the increased latencies observed may warrant further investigation.

Carbamazepine and lamotrigine in healthy volunteers: relevance to early tolerance and clinical trial dosage

This study was conducted to examine the effects of acute doses of lamotrigine (LTG) and carbamazepine (CBZ) in healthy subjects and determine whether the low tendency to impairment with LTG observed in animals applied to humans. Twelve healthy men participated in a placebo-controlled, balanced, double-blind comparison of the drugs on a series of psychomotor, autonomic, sensory, and subjective variables. Variables were analyzed by analysis of variance, and p < 0.05 was considered significant. Adaptive tracking and body sway were impaired by CBZ 600 mg. CBZ 400 and 600 mg impaired smooth pursuit eye movements and also reduced mean peak saccadic velocity. No differences from placebo occurred after LTG. CBZ 600 mg increased heart rate (HR), but no drug-related changes were noted in pupil size, salivary secretion, visual near point, or subjective effects. During the controlled study, mean plasma CBZ concentrations at 2 and 6.5 h after the 600-mg dose were 5.28 and 5.36 micrograms/ml; after LTG 300 mg, they were 3.16 and 3.00 micrograms/ml. Increased CBZ saliva concentrations were significantly associated (p < 0.01) with impaired adaptive tracking, smooth and saccadic eye movements and increased HR, and plasma concentrations were associated with impaired eye movements and body sway.

A microcomputer system for clinical signal analysis of vestibular laboratory

A vestibular laboratory system was implemented for clinical testing and medical examination of patients with balance disorders. Programs for analysis of postural control and eye movements were made for a microcomputer. The microcomputer system can be used by a nurse without technical education. The system has now been used for two years at the laboratory.

[Loading-doses of carbamazepine and diphenylhydantoin: use in high-risk patients]

Loading-doses of phenytoin (1000 mg) and carbamazepine (600 mg) were given orally respectively to 10 and 6 patients with uncontrolled epileptic seizures secondary to acute neurological disorders or alcohol withdrawal. In the phenytoin group age varied between 12-73 years and serum concentrations at 2, 4, 6, 8, 12 and 18 hours after drug administration were 7.6, 8.8, 8.7, 8.7, 7.2 and 6.5 micrograms/ml (means). A quantitative method did not detect important side-effects. In the carbamazepine group age varied between 25-56 years and serum concentrations at the same times were 3.9, 5.3, 6.5, 7.5, 7.4 and 8.2 micrograms/ml. Side-effects were discrete. Further medication was not necessary in the 24 hours after drug administration. Although both regimens controlled the clinical situation without relevant side-effects serum concentrations were sub-therapeutic in the case of phenytoin. We suggest the ideal phenytoin oral loading-dose is 1500 mg. The carbamazepine load produced therapeutic concentrations. The stability of serum concentrations for the period of the study shows that those regimens are useful in the subacute control of epileptic seizures in the maintenance treatment of status epilepticus and in alcohol withdrawal.

The effects of acrivastine (BW825C), diphenhydramine and terfenadine in combination with alcohol on human CNS performance

Two studies were performed to measure the effects of acrivastine (BW825C), an antihistamine, in combination with alcohol on the central nervous system. In one study acrivastine 8 mg, diphenhydramine 50 mg and alcohol 32 ml were administered alone and in combination and compared with placebo. In a second study terfenadine 60 and 120 mg and acrivastine 4 and 8 mg combined with alcohol 32 ml were compared with placebo and alcohol alone. Each study was a double-blind, randomised cross-over design using twelve healthy volunteers. Adaptive tracking, reaction time, body sway, eye movements and subjective effects were measured at intervals after treatments. Acrivastine 8 mg alone did not affect any of these measures in contrast with diphenhydramine. Acrivastine in combination with alcohol caused significantly more impairment of some of the tests than placebo or alcohol alone, but significantly less than diphenhydramine/alcohol, which also affected more tests. In the second study no significant differences were seen between the effects of alcohol alone and combinations of either terfenadine or acrivastine with alcohol. It was concluded that acrivastine 8 mg alone did not impair CNS performance in the tests used. In combination with alcohol significant impairment was seen, but this was less pronounced than after diphenhydramine/alcohol. The second study failed to demonstrate differences between drug/alcohol combinations and alcohol alone confirming that the effect of acrivastine in combination with alcohol is small.

Lamotrigine (BW430C), a potential anticonvulsant. Effects on the central nervous system in comparison with phenytoin and diazepam

Twelve healthy male volunteers received phenytoin 0.5 and 1 g, lamotrigine (a new anticonvulsant) 120 and 240 mg, diazepam 10 mg and placebo orally in a double-blind, cross-over, randomized trial. Maximum drug concentrations at 4 h, measured in plasma were 11.5 +/- 2.2 micrograms ml-1 for phenytoin and 2.7 +/- 0.4 micrograms ml-1 for lamotrigine. These levels were in the therapeutic range for phenytoin and the putative therapeutic range for lamotrigine. Side effects after diazepam (mainly sedation) and phenytoin (mainly unsteadiness) differed markedly from lamotrigine which produced no important side effects. Subjective effects as measured by visual analogue scales were caused by phenytoin and diazepam but not by lamotrigine. Diazepam impaired eye movements, adaptive tracking and body sway. Phenytoin impaired adaptive tracking, increased body sway and impaired smooth pursuit eye movement. Lamotrigine produced only a possible slight increase in body sway. There were significant correlations between performance and saliva levels of phenytoin and diazepam. It was concluded that the tests used were suitable for monitoring CNS effects of anticonvulsants and that lamotrigine possibly could have a more favourable CNS side effect profile than phenytoin.

Computerized analysis of voluntary eye movements. A clinical method for evaluation of smooth pursuit and saccades in oto-neurological diagnosis

To permit rapid and exact quantification of the oculomotor function in clinical practice, a computerized program has been designed for the recording and analysis of pursuit eye movements and voluntary saccades. In a pursuit sequence the subject tracks a moving target, projected onto a screen at a constant speed of 20 degrees/sec over a horizontal visual angle of 60 degrees. The pursuit sequence is followed by a refixation saccade when the subject rapidly shifts his gaze back to the starting point of the target. A complete test procedure consists of ten consecutive pursuit sequences and refixation saccades in each direction. The EOG signal is fed to a PDP11/23 computer for storage and analysis. The pursuit eye movements are quantified and arranged in five velocity intervals: less than 8, 8-16, 16-24, 24-32 and greater than 32 degrees/sec. The relative distribution of the velocity content is calculated for these intervals and presented in histogram form. Saccades superimposing on the smooth pursuit are identified and grouped according to amplitude and direction. The refixation saccades are quantified as mean peak velocities and also the highest and lowest velocities of the refixation saccades are determined. In a material of 70 healthy subjects, normative data and limits for pathological function were established. In the smooth pursuit, 69% of the velocity values were located within the 16-24 degrees/sec interval. Pathological limits were set for each velocity interval and impaired pursuit tracking ability was considered to be present when those limits were reached in at least three of the five intervals. Normal mean peak eye velocity of the refixation saccade was found to be 460 degrees/sec with a range of 354-575 degrees/sec. Application of the test procedure and method of analysis is described in two patients with impairment of the oculomotor function due to a disturbance in the cerebellar brain stem area.

The effects of the "vestibular sedative" drug, Flunarizine upon the vestibular and oculomotor systems

The effects of the "vestibular sedative" drug Flunarizine upon the oculomotor functions of pursuit and voluntary saccades and upon the vestibular response (to rotational stimuli) were assessed in twenty volunteer subjects. The study was then extended to three patients with chronic imbalance of central origin who had reported a beneficial symptomatic response to the drug. Three of the volunteer subjects were found to have a directional preponderance (presumed to arise from peripheral dysfunction). In the remaining seventeen normal subjects Flunarizine was found to reduce the amplitudes of fast phases of vestibular nystagmus. The directional preponderance in the other three subjects was redressed through production of fast phases which were of lower and more uniform amplitude. In the patients, in addition to a reduction in fast phase amplitude, there was a reduction or abolition of after nystagmus. In no case was any reduction in slow phase velocity observed. Pursuit and voluntary saccades were unaffected by the drug. It was concluded, on the basis that the fast phases of nystagmus are centrally generated, that Flunarizine has a central action rather than a depressant effect upon the vestibular end organ. In view of known oculomotor physiology and pharmacology it is proposed that vestibular sedatives act by depression of Type II vestibular neurons, and modification of the functional relationships between the vestibular nuclei, the perihypoglossal nuclei and the flocculus of the cerebellum. A trial of vestibular active drug is indicated particularly in patients in whom asymmetry of the vestibular response and/or abnormal after nystagmus is demonstrated.