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Ocular fixation test and ocular fixation index (OFI) never have been interpreted in terms of mathematical models, despite their widespread diffusion. However, ocular fixation is a typical case of visual-vestibular interaction, and mathematical models have proven very helpful in interpreting some mechanisms of this interaction, e.g. those of the optokinetic-vestibular interaction. In the present paper, a first attempt is proposed toward a model interpretation of OFI. By using very simple mathematical models, the hypothesis is tested that visual suppression of vestibular nystagmus results from direct action of smooth pursuit system (SPS). The aim is to draw consequences and recognize possible limits of this hypothesis. Dependence of OFI on SPS performance is examined. Although the available experimental data are insufficient for comprehensive validation of the model, the results agree with the current interpretations. In particular, quantitative support is given to the sensitivity of OFI to central vestibular diseases. Although the interpretation of visual suppression and OFI in terms of mathematical models is still at a very preliminary stage, models may provide a theoretical reference framework for the interpretation of new experimental results and/or suggest new test protocols.
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The purpose of this study is to investigate the diagnostic value of using the damped pendular rotation test (DPRT) (1) with an ocular fixation (ocular fixation test, i.e. OFT), and (2) in the dark with the eyes open, jointly with auditory brain stem response (ABR) audiometry. Impairment of ocular fixation was found in patients with either brain stem lesions, cerebellar lesions, or cerebellopontine angle tumors. A collective evaluation of the findings of OFT with those of ABR audiometry has suggested the possibility of differentiating upper brain stem lesions from lower brain stem lesions, tumors of the IVth ventricle, and cerebellar tumors. However, differentiating IVth ventricle lesions from tumors involving the cerebellar vermis extending into the IVth ventricle by this battery of tests was somewhat limited.
Effects of ocular fixation on pendular rotation nystagmus were investigated in 65 patients. There were 25 with peripheral vestibular or vestibulo-cochlear disorders, 17 with central vestibular disorders, five with congenital nystagmus, 16 patients over 60 years old with vertigo in whom peripheral vestibular disorders were ruled out, however, the causes were unknown. Damped pendular rotation test (DPRT) was performed both under darkness and employing mental arithmetic and under ocular fixation. These findings were related to those of caloric vestibular suppression test (VST) by Takemori and those of optokinetic pattern test (OKP), eye tracking test (ETT), and spontaneous nystagmus. Thirteen of 17 patients with central vestibular disorders and five with congenital nystagmus showed loss of visual suppression during ocular fixation in DPRT, whereas in cases of peripheral lesions, visual suppression was observed. Loss of visual suppression during ocular fixation in DPRT was often seen in cases of brainstem and cerebellar lesions. In brainstem lesions, perrotatory nystagmus was evoked during ocular fixation, whereas no nystagmus was seen in darkness with eyes open. In cerebellar lesions, perrotatory nystagmus was partly suppressed or decreased during ocular fixation. Relationships between the direction of the visual suppression during ocular fixation in DPRT and the side of the lesion were not apparent. Ocular fixation test in DPRT has a diagnostic value not only for central lesions, but for differentiating brainstem lesion from cerebellar lesion with the findings in DPRT under darkness. The findings under ocular fixation in DPRT are closely related to those of VST in cases of caloric nystagmus.
PURPOSE: (1) To assess the adequacy of the magnetic field coil method (MFCM) for measures of extreme gaze ocular fixation; and (2) to measure the accuracy of ocular fixation for a short duration at gaze angles of 10 to 40 degrees. METHODS: Seven subjects participated. Two experiments were performed on the same day. In both experiments, the head and eye were rotated in opposite directions. In the first experiment, search coil slippage was assessed using photographs of a scleral search coil worn on one eye. These photographs were taken with a slitlamp biomicroscope equipped with a digital photography system as subjects rotated the eyes through nasal angles up to 40 degrees. In the second experiment, measures of ocular position were made using the MFCM as the eye was rotated through nasal angles up to 40 degrees to fixate a light-emitting diode target under two conditions. In one condition, subjects simply aimed the eye at the target. In the other, subjects placed a foveal afterimage on the target as the target was viewed through a pinhole. RESULTS: Temporal search coil slippage >10 arc min was noted for three subjects. For one subject, this slippage occurred at gaze angles > or =20 degrees, whereas for the other subjects, the slippage appeared at gaze angles of > or =30 degrees. Ocular fixation had to be assessed from the differences in fixation position between the two conditions in the second experiment because of search coil slippage and because the relationship between the anterior and posterior portions of the eyes changed for some individuals as the gaze angle changed. Fixation was usually accurate (within 10 arc min). There were occasional instances where fixation errors >15 arc min occurred, but we believe that all but one of these cases were attributable to poor localization of the afterimage. CONCLUSION.: Scleral search coils can slip on some individuals in extreme gaze. Search coils may also be inadequate to indicate the direction of the fovea in extreme gaze for some individuals because the relationship between the anterior and posterior portions can change with gaze angle. Once artifacts associated with the MFCM and localization of the afterimage are accounted for, ocular fixation is almost always within 10 arc min of the fixation target at gaze angles of 10 to 40 degrees.
Patterns of ocular fixation in free-viewing tasks reflect aspects of visual attention and cognition. To quantify these patterns, fixations must be identified in raw eye movement data by applying explicit spatial and temporal thresholds. A temporal threshold of 200 ms is commonly used in clinical visuocognitive research, despite having been originally derived from a study of eye movements in reading. We systematically explored temporal fixation thresholds below 200 ms, using biologically relevant (human face) and abstract (complex geometric) stimuli. Short fixations (<200 ms) significantly altered spatiotemporal patterns of fixation for both the face and geometric stimuli, by increasing the number of fixations and the scanpath length. A threshold of 100 ms was found to discriminate fixations from other oculomotor activity effectively, and was consistent with current physiological and visuocognitive models. Statistical examination of fixation duration data for each subject suggested the median was a less biased and more robust measure of central tendency than the mean.
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.
The subject of investigation was the influence of ocular fixation on acquisition of habituation in experimental rotatory test in pigeons. The habituation training was performed in the three difference conditions: with full ocular fixation, fixation partly reduced and fixation excluded. Author confirmed that habituation with fixation excluded gave the best results of habituation of postural reflexes and head nystagmus in pigeons in rotatory training.
PURPOSE: To present a new technique of ocular fixation to restore and maintain the ocular alignment in primary position for patients with total third nerve paralysis. METHOD: We fixated the globe (medial rectus muscle insertion) to the medial palpebral ligament insertion at the anterior lacrimal crest by using nonabsorbable 5-0 polyester sutures in a prospective study of 5 patients (5 eyes) with congenital total third nerve paralysis. A large recession of the lateral rectus muscle (12 to 16 mm) was also performed in four patients. RESULTS: Four patients achieved satisfactory ocular alignment and one patient had residual exotropia. After an initial exotropic shift, no significant change in ocular alignment was observed during the follow-up period of 6 to 9 months. Mild fullness and congestion over the medial rectus muscle area was observed in the immediate postoperative period in all the patients, which resolved in about two months time. CONCLUSION: This technique of ocular fixation is easy, safe, and effective for the management of exotropia secondary to total third nerve paralysis.
The macaque lateral intraparietal area (LIP) has been implicated in visuospatial attention and saccade planning. Since area LIP also contains a representation of the central visual field, we investigated its possible role in fixation and foveal attention in a visual fixation task with gap (momentary disappearance of fixation point). In addition to the expected visual neurons ( n=119), two main categories were identified: (1) cells responding tonically both during the presence and momentary absence of the fixation stimulus( n=47); a subset of these neurons studied in a saccade task showed perisaccadic inhibition in half of the cases (14/27). The timing of this inhibition, however, is only loosely related to saccade timing; (2) cells responding mainly to the absence of the fixation stimulus, with either abrupt or gradual onset of activity during the gap ( n=62). During saccades, these neurons showed presaccadic buildup and/or postsaccadic activity, which was spatially tuned in about half of the tested cells (28/53). Ninety-one percent of the cells in the first category and 59% of the cells in the second category were located in the dorsal portion of area LIP (LIPd). These results are consistent with the hypothesis of an oculomotor-attentional network contributing to fixation engagement and disengagement in a subregion of LIP.
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BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric disorder without validated objective markers. Eye movement studies may be useful in providing objective criteria for characterizing the disorder. METHODS: We compared 53 children (29 girls) with ADHD to 44 healthy control children (18 girls) on a 21-sec fixation task. Large saccades (> 4 degrees ) away from the fixation point were analyzed. RESULTS: Children with ADHD made more large saccades that interrupted fixation than did control children (p =.001). Mean scores of the ADHD group did not change significantly with subsequent retesting on placebo (p =.11); however, there was poor intrasubject correlation (r =.16). CONCLUSIONS: Both boys and girls with ADHD made significantly more intrusive saccades during fixation than did control subjects, possibly reflecting intrinsic neurologic dysfunction; however, a probable "floor effect" obviates conclusions about the reliability of this measure.
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In previous work we reported that fixation stability did not deteriorate in older adults over relatively long viewing durations. In the present study we reanalyzed the data to examine potential aging effects on fixational control for viewing durations typically used in psychological experimentation. Monocular eye movements were recorded in 12 older and 12 younger observers using a dual Purkinje image technique, while observers fixated a stationary target. The two-dimensional scatter of eye positions was measured during nine viewing durations ranging from 100 ms to 12.8 s. Fixational control of the two groups was comparable at all of the viewing durations. Both younger and older observers were able to maintain fixation within an area several times smaller than the size of the fovea. Implications for aging studies that use briefly presented visual stimuli are discussed.
BACKGROUND: The examination of fixation on the fundus oculi is one of the main points in the diagnosis of amblyopia. Therefore it is necessary to describe the fixation ability and to clarify at what age children can fixate foveally and at what age this examination can be carried out, considering not only physiological aspects, but also co-operation reasons. PATIENT AND METHODS: Fixation on the fundus oculi was examined in 111 children aged between 1 and 25 months with the ophthalmoscop-star. This examination was carried out in 64 cases by a second and in 15 cases by a third examiner on the same day. RESULTS: During the first 3 months of age children cannot fixate foveally, one can observe instead, a kind of scatter at the posterior pole in a diameter of about 5 degrees. In the course of the 4, and 5, month of age foveal fixation develops. Repeated examinations of the same child on the same day by a 2, and 3, examiner reveal a very high rate of accordance (78%) of their results. CONCLUSIONS: The examination of fixation on the fundus can be carried out at 4 to 5 months of age. At that age one can differentiate quite reliable between a foveal and eccentric fixation as well as scatter at the posterior pole. The rate of accordance 78% with this fixation examination by several examiners shows that same reliability of this examination carried out in school children and adults. Comparing this result with fixation examination carried out with the Haidinger brushes then one must calculate with a fault rate of about 20% when examining with the ophthalmoscope, considering that the examination with Haidinger brushes as a reference examination.
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