Small Amplitude Saccades Research Articles

Short-latency fixational saccades induced by luminance increments.

We investigated the effect of peripheral visual stimulation on small-amplitude saccades that occur naturally during fixation. Two macaque monkeys were rewarded for fixating while a colorful stimulus flickered randomly in the periphery. Reverse correlation revealed a lawful relationship between the stimulus sequence and saccade occurrences: on average, a transient increase in stimulus intensity evoked saccades at a latency of approximately 70 ms. The spectral tuning of this increase was roughly, but not exactly, consistent with a pure luminance increase. We conclude that peripheral luminance increases can evoke fixational saccades.

Slow saccades in myogenic and peripheral neurogenic ophthalmoplegia Latent ocular myopathy in myotonic dystrophy

The difference of slow saccades between ocular myopathy and peripheral neurogenic ophthalmoplegia was studied. Slow saccades in three patient groups were examined. The first group consisted of 16 patients suffering from oculomotor or a bducens paresis. The second group consisted of eight ocular myopathy patients. The mode of decrease in saccade velocity was different between the two groups. The decrease of velocity in large amplitude saccades was more prominent than of small amplitude saccades in the first group. The decrease of velocity in small amplitude saccades was also prominent, like in large amplitude saccades in the second group. The mode of decrease in saccade velocity among the ocular myopathy patients was also found in the third group; seven myotonic dystrophy patients. These results suggested early involvement of extraocular muscles in these myotonic dystrophy patients, although all but one of them showed no apparent eye movement restriction.

Smooth pursuit eye movements in epileptics under antiepileptic medication.

1) Smooth pursuit eye movements (SPEM) were recorded in 18 normal, 20 schizophrenic and 50 epileptic subjects. Most of the schizophrenic and epileptic subjects were under medication, antipsychotic drugs in the former and antiepileptic drugs in the latter. 2) In schizophrenics and epileptics, rate of the saccadic component in SPEM was higher than that of normal controls. The rate of large amplitude saccades was higher in epileptics than in schizophrenics. 3) Though small amplitude saccades were usually superimposed on SPEM in schizophrenic patients, both large and small amplitude saccades superimposed irregularly on the smooth tracking curve were observed in epileptics, and overshoots or undershoots were also seen frequently. 4) SPEM disorder in epileptics was observed in more than half of patients receiving antiepileptic medication, especially in patients with a long period of treatment. SPEM disorder in epileptics tended to occur frequently in patients who received phenytoin in doses higher than a certain level; i.e. approximately 150 mg per day for a long period of time. 5) It is conceivable that the SPEM disorder represents a latent or subclinical cerebellar dysfunction due to phenytoin medication. It is suggested that the SPEM measurement is a useful tool to find out subclinical side effects of antiepileptic drug in the treatment of epilepsy.

Rapid eye movements in myasthenia gravis. II. Electro-oculographic analysis.

Voluntary saccades were studied by electro-oculography in ten patients with myasthenia gravis (MG) and in eight patients with other types of ophthalmoplegia. Despite limited range of eye movements, maximum velocities of 20 degree and 40 degree saccades in patients with MG were not significantly different from those in normal individuals, whereas maximum velocities in patients with other types of ophthalmoplegia were significantly decreased. In some myasthenic patients, small amplitude saccades were hypermetric and had high velocities, appearing clinically as "quiver" movements characteristic of MG. In MG the preservation of saccades with high initial velocities, even in the presence of severe ophthalmoplegia, suggests that muscle fibers generating rapid movements during saccades (twitch fibers) can be relatively spared when muscle fibers responsible for maintenance of excentric gaze (tonic fibers) are severely affected.