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Measurement of the ocular fixation index is very useful to assess the extension of pontocerebellar tumors. Determination of the other features of central impairment of the vestibular system completes this information.
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The visual fixation ability of learning-disabled children was evaluated after sensory integrative therapy had been administered for short or long periods of time. Children with hyporesponsive postrotary nystagmus displayed reduced oculomotor control skills, but the deficit was apparent only in those who had been in therapy for a shorter interval. These results present further support for the hypothesis that the learning disabled can be differentiated according to their nystagmus characteristics. In addition, very tentative evidence suggested that sensory integrative therapy may have been successful in ameliorating the fixation deficiency; however, further research into this possibility is needed. The data also indicate that oculomotor control dysfunction may be a mediating mechanism for at least part of the learning disabilities experienced by some learning-disabled children.
An adaptation of the stereotaxic micromanipulator is described which provides ocular support and stabilization during freehand vitrectomy. It consists of a baseplate for immobilization of the patient's head and an ocular fixation arm assembly which connects to the eye by grasping a special Flieringa ring sewed to the postlimbal sclera. The ocular fixation arm can be made alternately flexible or rigid, thereby providing needed ocular mobility or stability during the operation as is desired by the surgeon.
The effects of ocular fixation on per-rotatory nystagmus were studied during the course of the pendular vestibular stimulation test. If the subject is normal, or the disorder is peripheral, the nystagmus is abolished. Examples of these different results are presented.
A-scan readings must be taken along the visual axis for accurate axial length measurement. Various fixation targets, which ideally should not induce accommodation, are used to limit eye movements. In this study results using the Humphrey biometer under different fixation conditions were compared to establish the most suitable target. We also investigated corneal applanation effects by comparing optical and ultrasonic measurements of anterior chamber depth. We examined 12 randomly selected normal eyes of 12 young subjects. Three A-scans were recorded for each of five fixation conditions: spotlight at 6 m; Snellen letter at 6 m; solid probe's built-in green fixation target; Snellen letter at 6 m viewed through a -4.00 DS lens; spotlight at 6 m under cycloplegia (the comparison condition). Variability 'within' each fixation condition, estimated by the standard deviation for each subject, was equal throughout the 12 subjects for each fixation condition. Also variation was independent of size of the ocular dimension. The good agreement between the comparison condition and optical anterior chamber depth measurements indicated that the solid probe produced little applanation. Differences 'between' fixation conditions were investigated. It was concluded that a spotlight or letter at 6 m provides a suitable fixation target for biometry. Built-in fixation targets can produce significant errors.
Twelve normal subjects received standard caloric testing under the following conditions: 1) fixation, 2) Frenzel glasses in a dimly lit room, 3) eyes open in total darkness, and 4) eyes closed. Multiple nystagmus response parameters were evaluated and statistically compared for each condition. Fixation markedly diminished induced nystagmus and produced the largest coefficient of variation for each response parameter. Caloric testing with eyes closed resulted in periodic nystagmus suppression and a less distinct saw-toothed pattern. As with fixation, the coefficient of variation was consistently higher with eyes closed compared to eyes open in darkness or Frenzel glasses. It is concluded that caloric testing of the vestibulo-ocular reflex arc should be performed with eyes open in darkness or with Frenzel glasses.
The results of quantitative infrared horizontal eye movement recordings in 8 patients with progressive supranuclear palsy are presented. Some of the patients had total paralysis of vertical movements, but none had completely lost the ability to perform horizontal eye movements. All patients had a defect in ocular fixation previously undescribed in this condition: the universal presence of square-wave jerks. Analysis of refixation saccades demonstrated hypometria, slow velocity/amplitude relationships, and profound prolongation of duration. The pursuit abnormality, characterized clinically by "cogwheel" eye movements, represented the inability to match eye velocity to target velocity. The ratio of peak eye velocity to peak target velocity (pursuit gain) was 0.2 to 0.5. Defects in the vestibuloocular reflex included inability to increase the gain of the reflex (ratio of peak eye velocity to head velocity) during viewing of a visible, stationary target and failure to suppress the reflex when viewing a target rotating with the head.
Regional cerebral blood flow (rCBF) was measured in human subjects during saccadic eye movements by a 254-channel dynamic gamma camera. Focal rCBF increases were repeatedly observed in an area within the middle precentral and premotor regions which corresponds to the frontal eye field in humans. Our findings suggest that this region is localized between the "face" and "hand" areas in the precentral gyrus and extends anteriorly out of the primary motor strip into the adjacent premotor zone. In addition, saccades were associated with focal blood flow increases in regions corresponding to the frontal supplementary motor area and to the posterior temporooccipital visual association cortex. Similar changes in patterns of rCBF occurred during contralateral and ipsilateral horizontal saccades and also during vertical saccades, and did not differ between the right and left hemispheres. Focal rCBF increases were observed in the frontal eye field during several additional test procedures including ocular fixation and visual perception of a nonmoving target, auditory stimulation with closed eyes, and reading. It is presumed that these focal flow increases reflect increased localized neuronal activity and metabolic rate and therefore permit visualization of the cortical activation pattern associated with saccadic eye movements in humans.
Visuomotor ataxia is a disorder of movement performed under visual control. It can occur in the absence of disturbance of ocular fixation and in the absence of spatial agnosia. This disorder may extend over the whole visual field or it may be localized to one visual half-field, right or left. It may involve both hands or one hand only, so that visuomotor ataxia may be divided into: (1) Unilateral visuomotor ataxia, localized to a single field. In this case it may affect both hands or a single hand. It is direct when the hand is ataxic in the ipsilateral visual field and it is crossed when the hand is ataxic in the contralateral visual field; (2) Bilateral visuomotor ataxia, involving the whole visual field. Each hand may be ataxic only in the contralateral visual field, that is, bilateral crossed visuomotor ataxia; or in the ipsilateral field when it is called bilateral direct visuomotor ataxia. The observed clinical variations which are described here imply the existence of both direct and crossed visuomotor connections, the latter probably crossing the corpus callosum in the splenium.
The Otago photoscreener is an optical instrument which gives a very sensitive indication of the accuracy with which a subject's eyes are fixing and focusing. Early experience suggested that this instrument could be used effectively to screen for the presence of amblyogenic factors in pre-verbal infants. This communication describes the development of ocular fixation and focusing in 137 normal infants who were followed at regular intervals during the first year of life. Accurate fixation and focusing was found in 13% of three-month-old infants, in 68% of six-month-old infants and in 76% of one year olds. The levels of 'focusing' visual acuity obtained from the photoscreen data are considerably better than the levels of cortical acuity measured by the standard behavioral and electrophysiological methods. This suggests that human infants fix and focus accurately for a considerable period before they are able to perceive all the details obtained in their retinal images.
A patient with presenile dementia had instability of ocular fixation caused by small rapid horizontal eye movements (square-wave jerks). High resolution recordings of these eye movements were characteristic of microsaccades, which ordinarily occur during fixation, in all respects except amplitude. In addition, the patient showed complete absence of normal microsaccades. We suggest that microsaccades have become altered in our patient to form a clinical disorder of fixation.
The effects of opening of the eyes and of ocular fixation upon caloric nystagmus were investigated during the period of maximum intensity of caloric nystagmus in a series of 32 normal individuals. The percentage reduction in slow-phase velocity induced depended upon the test conditions, but, on the other hand, did not depend upon the temperature of the water applied as caloric stimulus. This latter fact favors the theory of visual suppression of the caloric test. Another striking finding was that a clear correlation definitely existed between the percentage reduction of suppression in slow-phase velocity and that in the multiplication product of amplitude by nystagmus frequency (P.A.F.) during the period of eye opening and ocular fixation. The percentage of suppression in slow-phase velocity is interchangeable with that in P.A.F., which broadens the practical scope of the routine test.
Analysis of the ENG records of 150 patients with well substantiated neurologic disease involving the structure of the posterior fossa revealed a high incidence of diminished optic fixation inhibition (DOFI) of caloric induced nystagmus. DOFI is defined as less than 50 percent decrease of speed of the slow phase when eyes are open and fixated. The whole group was subdivided into seven subgroups according to type and location of disease and the incidence of DOFI was found to vary significantly in the different subgroups. The highest incidence was found in the group of cerebellar mass lesions and in the group of degenerative diseases, most of which had cerebellar involvement. A review of the literature reveals work done by others showing that suppression of vestibular reflexes induced by high speed turning and also habituation of caloric induced nystagmus is dependent on optic fixation inhibition (opto-vestibular reflex.). It has been shown that the flocculonodular lobe of the cerebellum has an inhibitory effect on the effects of vestibular activity by both destructive and stimulating techniques. Afferent and efferent pathways between the cerebellum and primary vestibular reflex arcs have been extensively described. It has been shown that cerebellar nodulectomy severely interferes with acquisition of habituation and retention of previously acquired habituation. Since habituation and suprression of vestibular nystamus depend on optic fixation inhibition and equally on the cerebellum, it is reasonable to infer that the opto-vesitubular inhibitory reflex is mediated by the crebellum. The clinical data of the 150 cases were analyzed for correlation of DOFI and other cerebellar signs. This analysis gives a high incidence of correlation: 66 percent of the cases having DOFI also had other cerebellar signs, whereas only 19 percent of cases that did not have DOFI had other cerebellar signs. These data lend further support to the inference that the cerebellum is involved in mediation of the opto-vestibular inhibitory reflex. Under most circumstances visual perception of the environment during movement depends on an inter-reaction between the vestibulo-oculomotor and the opto-vestibular reflexes. Eye movements during head movements are entirely different with eyes closed than with eyes open and fixating. In fact, it can be shown that ocular fixation is far more efficient during head movements than it is during movement of an object with head stationary. It is probable that fixation in the former case is the result of vestibulo-oculomotor slow phase activity modified by the opto-vestibular inhibitory reflex and elimination of the fast phase. A defect in the latter should result in a sense of spatial insecurity during movement by virtue of altered visual perception. The opto-vestibular inhibitory reflex is a central descending reflex probably mediated through the cerebellum. It is easy to test during and ENG. It is essential to normal visual perception during head movement...
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