C. J. Lueck

Antisaccades and remembered saccades in Parkinson's disease.

Antisaccades were studied in ten patients with mild to moderate Parkinsons disease and ten age-matched normal controls. Remembered saccades and reflex saccades were assessed for comparison. In the population of patients who showed the previously reported abnormalities of remembered saccades, antisaccades were indistinguishable from those of controls in latency, gain and peak velocity. This finding implies that antisaccades are mediated through pathways which are unaffected by Parkinsons disease, and which are therefore presumably distinct from pathways mediating other voluntary saccades.

Auditory-visual interaction in the generation of saccades in man

SummaryFour normal human subjects were investigated for evidence of auditory-visual interaction in the generation of horizontal saccades. In a first experiment it was shown that the mean amplitudes of initial saccades from primary position to auditory targets were significantly affected by the simultaneous occurrence of a distracting visual stimulus. If both auditory and visual stimuli were in the same hemifield, the mean amplitude of initial saccades to a fixed buzzer position was consistently increased or decreased depending on the position of the visual stimulus. The phenomenon is felt to be analogous to the “centre-of-gravity” effect previously described for two simultaneous visual stimuli. It did not occur if visual and auditory stimuli were in opposite hemifields when a simultaneous visual stimulus caused a slight reduction of mean initial saccadic amplitude compared to the mean amplitude to buzzer alone. In this case the reduction was independent of visual stimulus position. Similar effects were seen for mean final eye positions. In a second experiment, a similar procedure was carried out, but the eyes started by looking at a point at 15° eccentricity. The same pattern of auditory-visual interaction was obtained in both experiments, consistent with the concept of eye-movement related movement of modality-specific sensory “maps” which has recently been shown to occur in the superior colliculus of primates.

Saccadic eye movements in Parkinson's disease: II. Remembered saccades--towards a unified hypothesis?

Ten patients with mild to moderate Parkinsons disease were compared with ten age-matched normal controls in a series of saccadic paradigms in order to test various hypotheses relating to the origin of the Parkinsonian saccadic defect. The paradigms comprised a reflex saccade paradigm, a standard remembered saccade paradigm, a remembered saccade paradigm with delayed centre-offset, and a remembered saccade paradigm with a second target flash immediately prior to saccade execution. Finally, subjects executed both reflex and remembered saccades in a standard remembered paradigm (the “two-saccade” paradigm). As has been reported previously, Parkinsonian subjects demonstrated hypometria on all remembered saccade paradigms, particularly the “two-saccade” paradigm. There was, however, no significant difference between the first three remembered saccade paradigms. These studies serve to refute a simple attentional capture hypothesis, and a hypothesis that suggests that the abnormality of remembered saccades is due to concurrent reflex saccade suppression. On the basis of the results, further hypotheses are advanced in an attempt to explain all published work on Parkinsonian saccades.

Saccadic Eye Movements in Parkinson's Disease: I. Delayed Saccades

The saccadic eye movements of nine patients with Parkinsons disease were compared to those of nine age-matched controls in two paradigms generating volitional saccades. In both paradigms, subjects had to make delayed saccades to peripheral LED targets: a peripheral target appeared 700 msec before a buzzer sounded, the buzzer being the signal to make a saccade to the target. In the first paradigm (“centre-off”), the fixation target was extinguished simultaneously with buzzer onset. In the second (“centre-remain”) it was not extinguished until 1000 msec later. The results showed that for outward saccades in both paradigms, there was no difference between Parkinsonian patients and controls, but saccadic latencies were significantly shorter in the “centre-remain” paradigm. The initial outward saccades were indistinguishable from the normal, reflex saccades of the same subjects. However, saccades returning to the centre (a type of remembered target saccade) were hypometric and showed multistepping. Both effects were more pronounced in patients with Parkinsons disease. The significance of these findings in terms of current hypotheses about the nature of the Parkinsonian saccadic deficit is discussed.

Vertical and horizontal saccadic eye movements in Parkinson's disease

vertical and horizontal saccades of 13 patients with Parkinsons disease were compared with those often age-matched controls using a ‘reflex’ paradigm. Contrary to previous suggestions that vertical eye movements are impaired or limited in Parkinsons disease, this study found no difference between patients and controls. There were no significant differences between groups in saccadic latency, gain, duration or peak velocity. This is in agreement with other studies of Parkinsonian saccades which have looked at horizontal ‘reflex’ (as opposed to ‘voluntary’) saccades. Within groups, a significant correlation was found between the latencies of vertical and horizontal saccades, but not the other saccadic parameters tested.

Increase in saccadic peak velocity with increased frequency of saccades in man

Twelve normal subjects (aged 22-80 yr, mean 47 yr) performed three blocks of 20 saccades made to LED targets stepped back and forth. The first and last blocks were performed at a (slow) rate of 0.18 Hz, while the middle block was performed at the faster rate of 1.15 Hz. Mean saccadic amplitude was unaffected by saccade rate, but latency and duration became shorter at the higher frequency. Most interestingly, the peak velocity increased by approx. 6% when saccades were performed at the higher rate. This increase was statistically significant, even after normalization for saccade amplitude. That saccadic frequency may affect saccadic peak velocity must be considered as a potential variable when analysing saccades.

Evidence for the occurrence of myotonia in the extraocular musculature in patients with dystrophia myotonica

Dystrophia myotonica (DM) is a multisystem disorder which has been reported to affect eye movements. There is, however, disagreement in the literature as to whether the observed slowing of saccadic eye movements is due to a central abnormality or due to abnormalities of the extraocular muscles themselves. A ‘warm-up’ effect is well known to occur in the peripheral muscles in DM. This effect involves a progressive decrease in the degree of myotonia observed with each successive relaxation during a period of repetitive contraction and relaxation of a given muscle. The authors have studied seven patients using two different paradigms to provide evidence that the ‘warm-up’ phenomenon can be demonstrated in extraocular musculature in patients with DM. Such an effect is not seen in controls. The observation of a ‘warm-up’ phenomenon suggests that the disorder of saccadic eye movements is likely to be due to an abnormality of the extraocular muscles themselves rather than a central mechanism.

Characteristics of remembered saccades in Parkinson's disease

Saccades to a remembered target use non-visual feedback and rely on a normal functioning of the projection from the caudate nucleus to the substantia nigra pars reticulata. The latter projection is known to be defective in Parkinsons disease and it seems therefore likely that remembered saccades are abnormal in such patients. In a series of three studies the characteristics of remembered saccades were compared with those of reflex saccades in patients with Parkinsons disease and normals. It was found that the remembered saccades of the patients were more hypometric than those of normals but that the final eye position was normal. Latency and peak velocity were normal as well. The patients exhibited an increased incidence of multistepping (“staircase saccades”). Using an inverse reconstruction technique, evidence was obtained for the presence of pulse doublets at the input of the oculomotor plant in such cases.

Saccadic eye movements in essential blepharospasm

SummaryTo provide evidence of an organic pathology for essential (idiopathic) blepharospasm, reflex saccadic eye movements in response to randomly stepped visual targets were assessed in seven affected patients and seven age-matched controls using the magnetic scleral search coil technique. The results indicate a significant prolongation in latency and a reduction in gain of horizontal saccades, and an increase in latency and reduction of peak velocity of large downward saccades. These findings suggest an organic component to the aetiology of blepharospasm, the pathology of which also appears to involve the oculomotor system. The pattern of the oculomotor disorder does not allow specific localisation but is consistent with the underlying pathology being localised in the basal ganglia.