Infrared Oculography Research Articles

The characteristics of dynamic overshoots in square-wave jerks, and in congenital and manifest latent nystagmus

Dynamic overshoots are seen after voluntary re-fixation saccades. They are microsaccadic movements which follow primary saccades and have no delay. The purpose of this study was to examine the prevalence and metrics of the dynamic overshoots seen after involuntary saccades. Using infra-red oculography we demonstrate that dynamic overshoots are a common occurrence in physiological square-wave jerks, congenital nystagmus and manifest latent nystagmus and that these overshoots are saccadic in nature and have the same dynamic characteristics as those seen following voluntary saccades. It is therefore likely that they share common neural commands to those dynamic overshoots seen after a volitional saccade. All dynamic overshoots are postulated to be the unwanted consequence of making a saccade and are simulated in a model of fast oculomotor behaviour which is consistent with known experimental results.

An effect of structured backgrounds on smooth pursuit eye movements in patients with cerebral lesions.

The oculomotor smooth pursuit system is driven by the slip of the target image upon the retina arising from errors in matching eye and target velocities. However, pursuit of an object moving against a structured background causes most retinal flow to be in the direction opposite to target movement. Central mechanisms allow these distracting signals to be overridden effortlessly. To isolate the anatomical substrate of this capacity we studied the effect of the presence of a structured background upon smooth pursuit in 26 patients with focal cerebral lesions. In normal control subjects, studies confirmed that a background has little effect upon pursuit. Eye movements were recorded by the scleral search coil method or by infra-red oculography. The target was a bright spot moving horizontally in a triangular waveform of amplitude +/- 11.25 degrees visual angle, at either 10, 20, 30 or 36.5 degrees/s. Data were collected in darkness and with a structured background: 14 patients showed a significant reduction of gain with a structured background, while the remaining 12 showed little or no effect. Comparison of the location of the cerebral lesions in these two groups suggested that lesions in the inferior parietal cortex (area 40) or in white matter containing parieto-frontal connections result in disruption of pursuit in the presence of a background.

Extraocular muscles are spared in advanced Duchenne dystrophy.

Fast-twitch extremity muscle fibers are preferentially affected in Duchenne's and Becker's muscular dystrophy. Since saccades are thought to be mediated by fast-twitch fibers, saccadic velocities would be expected to be decreased in these patients. Using infrared oculography, we found that the peak velocities of saccades in 3 patients with advanced Duchenne's or Becker's muscular dystrophy were normal. Clinical findings in 7 other patients with these forms of dystrophy were normal. This investigation is the first study of ocular motility in Duchenne's and Becker's muscular dystrophy. It demonstrates that extraocular muscle function is preserved and suggests that fast-twitch fibers in extraocular muscles possess properties that protect against degeneration.

A quantitative analysis of saccades and smooth pursuit during visual pursuit tracking: A comparison of schizophrenics with normals and substance abusing controls

The eye movements of schizophrenic patients are characterized by decreased smooth pursuit gain and an increased frequency of saccades. However, the nature of these saccades and their function during smooth pursuit has not been clearly defined. To address this issue we examined the eye movements of 22 schizophrenic patients, 20 substance abusing patients (primarily alcohol; some with concomitant cocaine and/or cannabis abuse), and 17 normal controls during a visual pursuit task using infra-red oculography. A computerized pattern recognition algorithm divided pursuit eye movements into two basic components: smooth pursuit and saccadic eye movements. The algorithm also determined eye position error and velocity error before and after each saccade. Schizophrenic patients had lower smooth pursuit gain ( p<0.02) and made more saccades during smooth pursuit ( p<0.02) than either comparison group. When saccades were assigned to subcategories based on direction and position error, only the frequency of ‘catch-up’ saccades differentiated schizophrenic patients from the comparison groups ( p<0.05). Smooth pursuit gain was negatively correlated with saccadic frequency among all three subject groups. Eye velocity preceding saccades was significantly lower among the schizophrenic patients, but pre or post saccadic position error did not differ among the three groups. Discrete analysis of the fine structure of visual pursuit tracking may lead to a better understanding of eye movement abnormalities in schizophrenia.

Divergent Nystagmus: Recordings from an Advanced System of Infra-red Oculography

Because of some limitations in photoelectric nystagmography, a new system of binocular infra-red oculography (BIRO) was developed. The advantages of BIRO are excellent linearity up to +/- 20 degrees horizontal eye movement, sensitivity of at least 0.1 degree of eye movement and the possibility of obtaining binocular recordings. In the course of a routine clinical evaluation, divergent nystagmus was recorded in 2 patients. This occurred both spontaneously and following caloric stimulation. A vascular brain stem pathology was strongly suspected from magnetic resonance imaging (MRI) studies. The possible mechanisms of divergent nystagmus are discussed.

Graves' Ophthalmopathy

Quantitative infrared oculography was used to record saccadic eye movements of 49 patients with Graves' ophthalmopathy. Peak saccadic velocities were decreased in those patients who developed or presented with optic neuropathy. This effect was more pronounced for larger eye movements. Peak saccadic velocity also decreased as total extraocular muscle volume and limitation of ocular motility increased. For any given extraocular muscle volume, peak saccadic velocity was 40 degrees/s slower in patients 40 years or older than in younger patients. The relationship between velocity and motility limitation was most pronounced for intermediate muscle volumes (8% to 15% of total orbital volume). Saccadic velocities in those patients with optic nerve compression often improved following treatment. This study demonstrated that eye movement recording was a useful adjunct in evaluation of patients with Graves' ophthalmopathy. Furthermore, age-related lowering of peak saccadic velocities implicated changes of extraocular muscle structure as a factor in the development of optic neuropathy.

Spasmus nutans. A quantitative prospective study.

Spasmus nutans includes ocular oscillations, head nodding, and anomalous head positions. No quantitative longitudinal study verifying the natural history of this self-limited condition has appeared in the literature. Using infrared oculography, we prospectively examined the eye movements of otherwise neurologically normal infants in whom a diagnosis of spasmus nutans had been made. At this writing the ocular oscillations and head movements in two of the children were clinically absent, thereby confirming the diagnosis. The ocular movements are characterized by a phase difference between the oscillations of each eye that varies both during one recording session and during development. The dissociated, pendular nystagmus consists of high-frequency oscillations that may be disconjugate, conjugate, or purely uniocular.

Waveform characteristics in congenital nystagmus.

Using infra-red oculography, electro-oculography and fundus video-recordings, waveform characteristics (amplitude, frequency, waveform shape and foveation) were examined in over 150 individuals with congenital nystagmus. For many of the subjects the nystagmus exhibited marked variability in both space and time. The sources of this variability were explored and the state of attention of the observer was found to be a dominant factor. The waveform and precision of foveation were not found to be related to any one classification group (eg. albino or idiopathic).