Measurement of eye movements by contact lens techniques: analysis of measuring systems and some new methodology for three-dimensional recording.
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Contact Lenses↗
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Impairment of spatially directed attention in patients with probable Alzheimer's disease as measured by eye movements.
OBJECTIVE: To investigate changes in spatially directed attention in patients with a diagnosis of probable Alzheimer's disease (AD). BACKGROUND: Impaired attention in patients with probable AD has not been the subject of extensive research. Yet recent reports suggest that attentional deficits may be an important early feature of the disease in a subset of patients. SETTING: University hospital center studying dementia and aging. SUBJECTS: Ten mild to moderately impaired patients diagnosed as having probable AD, by National Institute of Neurologic and Communicative Diseases and Stroke criteria, and 11 healthy age- and education-matched controls. MEASURES: Eye movements were recorded as subjects participated in two experiments designed to measure spatially directed attention. Subjects were instructed to (1) attend to and fixate a target appearing randomly to the right or left of a central marker and (2) direct attention to and fixate a target appearing randomly in one of four peripheral locations. RESULTS: Patients with probable AD exhibited fewer accurate trials and longer saccade latencies in both tasks. As a group, patients performed worse in the second task that placed increased demands on attention. However, the performance of patients in this second experiment varied. Four patients performed significantly worse than all other patients, while three patients performed as well as controls. Errors in the second task were reviewed to identify specific types of attentional deficits. Six empirically derived error patterns were classified into one of two major categories: perseveration and impersistence. Seven of 10 patients made greater than 50% errors of perseveration, and three of 10 made greater than 50% errors of impersistence. CONCLUSIONS: Impairment of attention may be an early feature of AD and a prominent clinical characteristic of some patients. The differences observed in error types made by patients may reflect the varied distribution of neuropathologic changes affecting structures that mediate aspects of attention. The architecture of eye movements can be used as a physiologic measure that should provide useful information for the diagnosis and clinicopathologic subtyping of patients with AD.
Aged↗
Occupational lead exposure. Effects on saccadic eye movements.
Quantitative measures of saccadic eye movements were examined in 52 lead exposed autobody shop workers and 52 age matched controls with no history of occupational lead exposure. Three characteristics of saccadic eye movements were studied: 1) saccade accuracy; 2) number of overshoots; and 3) maximum velocity. The results indicated that workers exposed to inorganic lead showed a decrease in saccade accuracy and an increase in overshoots compared with controls. Saccade maximum velocity was lower in lead exposed workers than in controls but the difference was just short of statistical significance. Correlations between measures of saccadic eye movements and indicators of lead absorption--blood lead (Pb-B) and zinc protoporphyrin (ZPP) levels--were analyzed in the lead exposed workers. Saccade accuracy was negatively correlated with both Pb-B and ZPP levels. The number of overshoots was not correlated with either Pb-B or ZPP levels. Saccade maximum velocity was not correlated with Pb-B, however, there was a significant negative correlation with ZPP. Age effects observed in the control group were disrupted in lead exposed workers. In addition, saccadic eye movements in younger workers (below 30 years old) were more affected by exposure to inorganic lead than were saccadic eye movements in older workers (50 years and older). It is proposed that these findings are consistent with a relatively rapid buildup of metabolically active lead burden observed in the study group. The data suggest that quantitative assessment of eye movements may be an important tool for studying subclinical central nervous system (CNS) dysfunction due to inorganic lead exposure.
Adult↗
Recording three-dimensional eye movements: scleral search coils versus video oculography.
PURPOSE: This study compared the performance of a video-based infrared three-dimensional eye tracker device (Chronos) with the scleral search coil method. METHODS: Three-dimensional eye movements were measured simultaneously with both systems during fixation, saccades, optokinetic stimulation, and vestibular stimulation. RESULTS: Comparison of fixation positions between -15 degrees and +15 degrees showed that horizontal and vertical eye position signals of the two systems were highly correlated (R2 = 0.99). Torsion values measured by coils and the video system were significantly different (P < 0.001). Saccade main sequence parameters of coil and video signals were in good agreement. Gains of torsion in response to optokinetic stimulation (cycloversion and cyclovergence) were not significantly different (P > 0.05). Gain values of the vestibulo-ocular reflex as determined from coil and video signals showed good agreement for rotations. However, there was more variability in the video signals for translations, possibly due to relative motion between the head and cameras. CONCLUSIONS: Lower time resolution, possible instability of the head device of the video system, and inherent small instabilities of pupil tracking algorithms make the coil system the best choice when measuring eye movement responses with high precision or when involving high-frequency head motion. For less demanding and for static tests and measurements longer than a half an hour, the latest generation infrared video system is a good alternative to scleral search coils. However, the quality of torsion of the infrared video system is less compared with scleral search coils and needs further technological improvement.
Adult↗
Asymmetrical vertical phorias indicating dissociated vertical deviation in subjects with normal binocular vision.
We measured the symmetry of phoria angles in six normal subjects. Subjects were selected on the basis of good visual acuity and stereopsis, normal binocular eye alignment and, apart from mild refraction errors, absence of ocular abnormalities. They were instructed to look at a word on a reading chart at 2 m distance. Each measurement consisted of five subsequent intervals of 5 s duration. During these five intervals viewing was binocular, with the right eye only, binocular, with the left eye only, and binocular, respectively. Each experiment consisted of twelve measurements. Eye movements were measured with scleral coils suited for measuring in horizontal, vertical and torsional directions. Five out of six subjects displayed an asymmetrical vertical phoria; one subject showed an alternating hyperphoria; four displayed a left over right vertical phoria that was largest for left eye occlusion. Only one subject showed a symmetrical vertical phoria. Both the size of the vertical phorias and the size of the asymmetries in these vertical phorias were very small: on average 0.16 +/- 0.01 and 0.17 +/- 0.01 degree, respectively. The direction of the vertical phoria asymmetries (the largest left over right was found with left eye occlusion) and the fact that asymmetries were found more often in vertical than horizontal and torsional phorias suggest that these asymmetries are related to dissociated vertical deviation. These results suggest that dissociated vertical deviation, often observed in subjects with a disruption of binocular vision early in life, reflects the enhancement of a phenomenon that is present in normal subjects as well.
Adult↗
Quantitative measurements of eye movements in a patient with Tullio phenomenon.
The Tullio phenomenon consists of vestibular symptoms on exposure to high-intensity acoustic stimuli, reflecting pathological stimulation of semicircular canals or otoliths. We report a patient with posttraumatic Tullio phenomenon to illustrate how precise measurement of eye movements during auditory stimulation, using the magnetic search coil technique, may characterize movements that are not clinically apparent or easily measured by other means. Such measurements in patients with surgically verified lesions may further elucidate the mechanisms responsible for this phenomenon.
Acoustic Stimulation↗
Does the FOUR score correctly diagnose the vegetative and minimally conscious states?
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Adolescent↗
Dynamic assessment of disparity vergence ramps.
Previous work has shown that the disparity vergence eye movement system responds to inward (i.e., convergent) ramp stimuli with both smooth and step-like behavior depending on target velocity. The responses to diverging ramp stimuli have not been previously studied, but convergence and divergence responses to other stimuli often show different behaviors. Converging and diverging 6 degrees/s ramps were presented to four subjects over a stimulus range of 2 degrees-20 degrees. Step-like behavior was seen in both convergence and divergence responses, but the dynamics was different. For divergent ramps, the peak velocity of each step-like movement decreased as the stimulus moved away from the subject, but no such trend was observed for convergence. The step-like behavior seen in divergence supports the hypothesis that the transient component is active in disparity divergence similar to the transient component proposed for convergent movements. However, the transient component in divergence may be dependent on stimulus position which is not the case for convergence.
Adolescent↗
The sub-clinical see-saw nystagmus embedded in infantile nystagmus.
A transient, decompensated vertical phoria in an individual with infantile nystagmus syndrome (INS) resulted in two images that oscillated vertically-a diplopic oscillopsia. Ocular motor studies during the vertical oscillopsia recreated by vertical prisms, led to the identification of a sub-clinical see-saw nystagmus (SSN), present under the prism-induced diplopic condition. Retrospective analysis of ocular motor recordings made prior to the above episode of vertical diplopia revealed the presence of that same sub-clinical SSN. The SSN had not been detected previously despite extensive observations and recordings of this subject's pendular IN over a period of forty years. Three- dimensional search-coil data from fourteen additional INS subjects (with pendular and jerk waveforms) confirmed the existence of sub-clinical SSN embedded within the clinically detectable horizontal-torsional IN in seven of the fifteen and a sub-clinical, conjugate, vertical component in the remaining eight. Unlike the clinically visible SSN found in achiasma, the cause of this sub-clinical SSN is hypothesized to be due to a failure of the forces of the oblique muscles (responsible for the torsional component of the IN) to balance out the associated forces of the vertical recti; the net result is a small, sub-clinical SSN. Thus, so-called "horizontal" IN is actually a horizontal-torsional oscillation with a secondary, sub-clinical SSN or conjugate vertical component. The suppression of oscillopsia by efference copy in INS appears to be accomplished for each eye individually, even in a binocular individual. However, failure to fuse the two images results in oscillopsia of one of them.
Diplopia↗
Oculopalatal myoclonus: eye movement studies, MRI findings and the difficulty of treatment.
Two cases of oculopalatal myoclonus with bilateral horizontal gaze palsies are presented. The abnormal vertical eye movements developed several months after brain stem haemorrhage. Eye movement measurements showed rhythmical vertical eye movements at similar rates (2.3 Hz and 2.4 Hz), unaffected by attempts to fixate, converge or gaze in any direction. T2-weighted MRI scans showed bilateral enlargement of the inferior olivary nuclei in both cases, which confirms the expected pathology previously demonstrated on autopsy. Both patients had severe oscillopsia and an attempt was made to improve this by bilateral disinsertion of the vertical rectus muscles. The pendular eye movements continued but were greatly reduced, in one case enough to relieve the oscillopsia. However, after 6 months retrobulbar botulinum toxin was required to continue to provide relief from the oscillopsia. Other treatment options, including pharmacological agents, are discussed.
Aged↗
Use of infrared TV cameras built into head-mounted display to measure torsional eye movements.
PURPOSE: The head-mounted display (HMD) has produced conflict between visual and vestibular stimuli because the HMD image does not move with the head motion of the wearer. The HMD can show binocular parallax three-dimensional (3D) images, in which vergence and accommodation conflict. Thus, the HMD may affect the normal visual/vestibular functions. We attempted to develop a system that makes possible the measurement of torsional eye movements, vergence eye movements, and pupillary responses of the HMD wearer. METHODS: Our apparatus is composed of two infrared CCD cameras installed in the HMD. Iris images produced by these cameras are analyzed by a personal computer using free software. Further, a third camera fixed on the HMD projects an image of the view as the subject sees it, via video tape recorder or frame memory to the HMD. Images can be stored, replayed, or frozen. RESULTS: Our system can measure torsional eye movement with 0.20 degrees resolution every 1/30 (or 1/60) seconds even though the pupil size alternates during measurement. Binocular eye movement and pupillary response are also measured. CONCLUSION: A system was developed which can be used for assessment of the effect of 3D HMD on the visual system. A third camera coupled with HMD can control visual stimulus independently of head motion (vestibular stimulus).
Eye Movements↗
Rapid eye movement sleep measures of Alzheimer's-type dementia patients and optimally healthy aged individuals.
It has been suggested that rapid eye movement (REM) sleep measures may be useful in the differential diagnosis of affective disorders. To determine what changes, if any, of REM measures occur in Alzheimer's dementia we examined the REM sleep of nine control and nine mild, nine moderate, and nine severe dementia subjects with probable Alzheimer's disease (AD). Control and mild and moderate AD groups were screened to exclude major depression. REM latency, REM time, REM activity, and REM density were examined. Results indicated that REM sleep measures are minimally affected by mild dementia. None of the REM sleep variables reported here successfully discriminated mild AD subjects from controls. However, REM time and REM latency were significantly affected in later stages of dementia. Total time in REM and REM latency successfully classified control and moderate-severe AD patients. In addition, the pattern of REM density across the night was also affected by severity of dementia. The results of this study, when compared to published REM measure findings in major depression, indicate that with proper cautions REM sleep measures may prove useful in the differential diagnosis of dementia and depression in geriatric patient populations.
Aged↗
Eye position signals in the abducens and oculomotor nuclei of monkeys during ocular convergence.
Many neurons in oculomotor pathways encode signals related to eye position. For example, motoneurons in the third, fourth, and sixth cranial nuclei discharge at highly regular rates during fixation intervals. During fixations of far targets, their tonic discharge is linearly related to conjugate eye position. Previous studies provided evidence that premotor cells in brainstem pathways also encoded conjugate eye position. McConville et al. (this volume), however, measured eye movements during binocular fixations when the eyes were converged and concluded that the position signal encoded by premotor position-vestibular-pause (PVP) cells in the vestibular nuclei is related to monocular (right or left) eye position rather than to conjugate eye position. This surprising relationship would not have been noticed in earlier studies that measured the movements of only one eye (using a single eye coil) or that measured only the conjugate movements of the two eyes (using bitemporal EOG electrodes). How general a feature of oculomotor signal processing is this finding? In this paper, we re-examine the eye position signal in abducens and oculomotor neurons when the movements of the two eyes are conjugate and when they are disjunctive and therefore disassociated. The data suggest that abducens neurons (AMNs and AINs) and oculomotor neurons (putative medial rectus motoneurons), unlike PVP cells, are not monocular but encode mixtures of right and left eye position signals.
Abducens Nerve↗
The operating version of the Eye Tracker, a system to measure saccadic eye movements.
The operating version of the Eye Tracker, a transducer and system using a technique to bounce infrared light off the eye to measure saccadic eye movements in any X-Y position is presented in this paper. Discussed is the method of reading and analyzing eye movement data using a 24-channel infrared optoelectronic array and computer algorithms that utilize a linear regression model to interpret and determine eye location, the 24-channels used to ensure accurate reading of eye position. Accuracy is also maintained by a signal processing system that attenuates incident light as well as ambient light. Also discussed is a novel method of mounting the infrared array on hemispherical shaped eyepieces that in turn are mounted on goggles styled after an ophthalmologist's test frames that is comfortably worn and adjustable in size to fit any subject. A computer controlled, wall mounted light bank facilitates targeting for eye movements. The Eye Tracker is built to meet standards of a professional medical device manufacturer following typical mechanical, electrical, and safety techniques unique to device packaging.
Diagnosis, Computer-Assisted↗
Rapid eye movement sleep eye movements in schizophrenia and depression.
OBJECTIVE: To investigate the specificity of rapid eye movement (REM) sleep eye movement measures in schizophrenics, depressives, and nonpsychiatric controls. DESIGN: Survey. SETTING: Inpatient psychiatric hospital. STUDY PARTICIPANTS: Volunteer sample of male veterans who met Research Diagnostic Criteria (RDC) for schizophrenia (n = 21) or major depressive disorder (n = 24), or male veterans recruited from the community with no history of psychiatric illness (n = 13). Patients with a concurrent RDC diagnosis of alcoholism were excluded. After data collection, three schizophrenics, two depressives, and one nonpsychiatric control were eliminated because of two or fewer REM periods on either of the two recording nights. INTERVENTION: None. MAIN OUTCOME MEASURE: Computer-detected total night and within-night measures of REM sleep eye movement density, ie, the ratio of eye movement counts to stage REM minutes. RESULTS: Using a 95% confidence interval, schizophrenics, depressives, and nonpsychiatric controls did not differ in total night or within-night measures of eye movement density. Within nights, eye movement density increased across REM periods in the schizophrenics and nonpsychiatric controls; the depressives showed a flatter within-night distribution associated with their older age. CONCLUSIONS: A broad range of REM sleep eye movement densities characterize both schizophrenics and depressives and substantially overlaps the normal range. Abnormalities of REM sleep eye movement activity should not be considered a biological marker for affective illness.
Adult↗
[The scanning laser ophthalmoscope and its application as a measuring system for eye movements].
This paper describes the present status of scanning laser ophthalmoscopy (SLO) for three-dimensional recordings of monocular eye movements. The measurement principle is based on tracking suitable landmarks on either the ocular fundus or the anterior eye pole. In addition, since it incorporates a special feature allowing the projection of visual test stimuli onto precisely controllable locations of the retina, SLO introduces a novel method of studying the relationship between retinal activity and eye movement analysis. The clinical use of SLO for the evaluation of vestibular otolith function by measuring the rotation of the ocular fundus image in response to lateral head tilt (ocular counterrolling reflex, OCR) is illustrated.
Equipment Design↗
Comparisons of eye movements before and after a speed-reading course.
BACKGROUND: The techniques of speed reading are widely used and generally accepted, but few studies have investigated whether- and how-speed reading actually improves reading ability in the typical reader. METHODS: Using the Ober2, an infrared monitoring device that accurately tracks eye movements, we measured the eye movements of 59 students. The Ober2 calculates reading speed, number of fixations per 100 words, number of words seen in each fixation, number of regressions per 100 words, and duration of fixation. Comprehension was assessed with ten detailed true or false questions. RESULTS: One group of the students (n = 25) participated in a speed reading class; the other group (n = 34) did not. After completion of the course, all 59 were re-measured on the Ober2. The speed-reading group improved significantly in five of the six aspects tested. Comprehension for the speed reading group showed an insignificant decrease. CONCLUSIONS: We conclude that measurable changes in reading eye movements accompany successful completion of a speed-reading course.
Adult↗
Behavioral calibration of eye movement recording systems using moving targets.
Equipment used to measure eye movements must generally be calibrated to the individual subject. Some methods of measuring eye position are quite non-linear, requiring that the system's output be linearized. We describe an approach of behavioral calibration and linearization that utilizes tracking of moving targets. The key aspect of this approach is to use tracking of horizontally moving targets to calibrate vertical eye position and vice versa. This method is especially convenient for use with cats, whose fixation of eccentric stationary targets is often unreliable. It allows one to obtain an accurate calibration without having to judge whether or not tracking saccades reliably hit the target.
Animals↗