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Biomedical subjects

M J Steinbach

Publications and source records attributed to M J Steinbach.

At least 19 recordsLinked to original sources
PubMed1999

Monocular horizontal OKN in observers with early- and late-onset strabismus.

Several reports on monocular optokinetic nystagmus (OKN) in observers with strabismus have found that asymmetry of OKN tends to occur in both eyes of observers with an early onset of strabismus but only in the deviating eye of those with a later onset of strabismus. Our objective was to quantify and compare the magnitude of the OKN asymmetry in each eye as a function of observer's age at onset of strabismus. We studied monocular OKN in ten observers with early-onset (up to 24 months of age), seven observers with late-onset (after 24 months of age) unilateral strabismus, and 12 normally sighted control observers. In the deviating eye, observers with early-onset strabismus showed large OKN asymmetries in favour of nasalward motion while observers with late-onset strabismus showed smaller OKN asymmetries in that eye. The majority of early- and late-onset observers showed near normal OKN in the non-deviating eye although the early-onset observers showed bilateral asymmetries more often. These findings may be due to both age at onset of strabismus and chronological age and are discussed in terms of the issue of plasticity or recovery of function.

Adolescent↗
PubMed1999

Egocentric localization: visually directed alignment to projected head landmarks in binocular and monocular observers.

PURPOSE: To determine the accuracy and precision with which humans align moving, non-moving, point-like and linear stimuli to three head landmarks projected to a frontal plane. Monocularly enucleated and binocularly normal subjects, performing monocularly, were tested. METHODS: Experimental tasks consisted of aligning the stimulus, a luminescent target, using a remote steering wheel control, to three projected landmarks; the nose, and the outside edge of each ear. Experiments were performed with a fixed [static] linear stimulus and a small dynamic stimulus, and then with a fixed stimulus at both a very close and an intermediate distance. RESULTS: The data from the monocular enucleated observers showed better accuracy in some conditions but their variable errors were larger than those of the controls. CONCLUSIONS: We propose that, for the alignments of the enucleated monocular subjects, a) the increase in accuracy is consistent with a shift of the egocenter in the direction of the remaining eye, and b) the decrease in precision may be due to the fact that the egocenter does not correspond to the mid-sagittal or median plane. This disparity would require adjustments to be learned in order to perform tasks involving visually directed alignments to the self.

Adolescent↗
PubMed1998

Registered eye position: short- and long-term effects of botulinum toxin injected into eye muscle.

Botulinum toxin is sometimes injected into human eye muscles as an alternative to surgery in the correction of strabismus. Within minutes of botulinum injections into ungulate eye muscles, proprioceptive discharge from muscle spindles decreases dramatically. It is only over 7-48 h, however, that surgically treated strabismus patients usually show an altered proprioceptive signal about eye position, presumably from the palisade endings attached to the global multiply innervated fibers. How quickly will botulinum toxin alter proprioceptive registration of eye position in humans? First, to examine the short-term effects, we measured open-loop pointing responses (which requires knowledge of eye position) in six strabismus patients preinjection and then over a 45 min postinjection period, and in six normal controls over the same time period. Second, to examine the long-term effects, 13 strabismus patients were tested preinjection and then daily over the next 3 weeks, and three normal controls over the same time period. We compared their open-loop pointing responses with the injected eye fixating the target to the photographically determined position of the occluded other eye (a measure of where the patient would point if eye position were determined by efference, not proprioception). There were three groups of patients: esotropes with no previous injection, exotropes with no previous injection, and exotropes with previous injection. First, all patients showed significant correction of their tropias. Second, over the short-term, there was no difference in pointing responses found between the patients and the controls (t(18) = -1.427, P = 0.1706). Third, over the long-term, however, the difference between the pointing responses and eye position information was compared among the four groups across four posttests and a significant difference found (F3,12 = 58.988, P < 0.00001). Only in patients with no previous injections was there altered proprioceptive feedback about eye position. Also, injections into the medial rectus induced a significantly greater proprioceptive response than those injected into the lateral rectus. In humans, botulinum toxin alters proprioception from eye muscles only over the long-term. We suggest that the toxin temporarily affects proprioceptive feedback from palisade endings.

Adult↗
PubMed1998

The Cyclops effect in adults: sighting without visual feedback.

When asked to look through a tube, younger children place it at the bridge of the nose, and not over one eye: the Cyclops effect. This is a natural response to a median plane egocenter. With maturity, the Cyclops effect disappears as we learn to overcome the consequences of an egocenter between the two eyes, and instead, to use the "preferred" eye. We videotaped adults (n = 14) and children with normal vision (n = 30), children with comitant strabismus (n = 14), and adults and children (n = 14) with one eye enucleated as they attempted to look through a plastic tube. Immediately in front of the face was a liquid crystal window that could be either transparent or opaque. As the tube was raised, the window was made opaque--blocking sight of the target, their hands, and the tube. Most binocular observers placed the tube approximately at the bridge of the nose. This was significantly different from the response of the enucleated observers who put the tube 75% of the way to the remaining eye (P = 0.0001). All observers align, on average, with the measured location of their egocenter when asked to perform a monocular task without visual cues. Deprived of visual feedback, binocular observers show the Cyclops effect, regardless of age.

Adolescent↗
PubMed1998

Vertical latent nystagmus component and vertical saccadic asymmetries in subjects with dissociated vertical deviation.

PURPOSE: This study was conducted to quantify the vertical component of a latent nystagmus observed in subjects with dissociated vertical deviation (DVD), as well as to provide further evidence for vertical saccadic asymmetries in these individuals. METHODS: Binocular eye movements of subjects with DVD were recorded in two dimensions using a noninvasive video-based eye tracker while cover/uncover tests, alternate cover tests, and vertical saccades were performed. RESULTS: A small amplitude (1.5 degrees or less) vertical component of latent nystagmus can be observed in some subjects with DVD and is larger in the deviating eye than in the viewing eye. The frequency of the vertical nystagmus component is the same in each eye for any given fixation condition but may change depending on which eye is fixating. DVD in the presence of a vertical component of latent nystagmus can be adequately modeled by the algebraic sum of an exponentially decreasing velocity DVD and a nystagmus with an exponentially decreasing slow phase velocity. In general, the occluded eyes of DVD subjects make smaller downward saccades than the viewing eyes. CONCLUSIONS: It is possible but not obligatory that DVD subjects will have a vertical component of latent nystagmus. Algebraic summation of an exponentially decreasing velocity DVD and a vertical component of latent nystagmus provides a more parsimonious explanation of the observed saccadic eye movements than modeling the DVD itself as a combination of vergence and saccadic movements. Subjects with DVD show a range of saccadic yoking from nearly complete saccadic conjugacy to nearly complete dissociation.

Adult↗
PubMed1997

Head turn in 1-eyed and normally sighted individuals during monocular viewing.

OBJECTIVE: To determine the incidence and magnitude of head turn in persons unilaterally enucleated at an early age and in normally sighted persons patched monocularly. SETTING: The Hospital for Sick Children, Toronto, Ontario. PARTICIPANTS: Fifty-two unilaterally enucleated children and adults without nystagmus (median age, 10 years) who were enucleated at an early age (median age, 18 months) due to retinoblastoma and 28 normally sighted children and adults. METHODS: Enucleated subjects were videotaped while walking 15 m toward a camera under 2 conditions: (1) fixation relaxed (just looking at the camera) and (2) fixation forced (trying to identify a small fixation target on the camera). Control subjects were tested in the fixation forced condition only. Head turn incidence and magnitude were independently rated. Three categories of head turn were used: "obvious" (> 10 degrees), "small" (5 degrees-10 degrees), and "no" (0 degree-4 degrees). RESULTS: In the fixation relaxed condition, 22 (42%) of 52 enucleated subjects exhibited head turn; when fixation was forced, the incidence increased to 25 (58%) of 43 subjects. Head turn was virtually always in the direction of the missing eye. Incidence and magnitude of head turn were unrelated to age at enucleation or number of years since enucleation. In the control group, there was no consistent finding of head turn across subjects when 1 eye was patched. CONCLUSIONS: One-eyed children frequently exhibit head turn unrelated to the presence of nystagmus. The direction of the head turn is "adaptive" because occlusion by the nose in the lower contralateral field is reduced.

Adolescent↗
PubMed1997

Vertical eye position control in darkness: orbital position and body orientation interact to modulate drift velocity.

How stable is vertical eye-in-head position control in darkness when no visual targets are present? We evaluated this while varying both body-in-space orientation and eye-in-orbit position in six subjects who were free from oculomotor/vestibular disease. Vertical eye movements were monitored using a CCD-video tracking system, and results were confirmed on one subject with the magnetic search coil. Three body orientations were used: (1) seated upright; (2) supine; and (3) prone. In each of these body orientations starting eye-in-orbit position was varied in quasi-random order from -20 to +20 deg, while vertical eye drift was monitored for a 90 sec period at each position. Subjects were instructed to hold their eyes as steady as possible. The relationship between body orientation/eye position and vertical eye drift velocity was examined using a linear regression technique. In contrast to prior clinical reports, normals exhibit a vertical nystagmus/drift in darkness. Moreover, slow-phase eye velocity was found to be dependent on eye-in-orbit position in the upright and supine body orientations. This pattern of eye drift mirrors Alexander's Law, with significantly increased drift velocities when subjects looked in the direction of their re-centering saccades (P < 0.05 or better). Body-in-space orientation also modulated the eye drift velocity, with significant differences in rate of eye drift (P < 0.05 or better) between extremes of body orientation (supine and prone) for five out of six subjects. The stability of the vertical oculomotor control system in the absence of visual input is strongly affected by body-in-space orientation and eye-in-orbit position: manipulating either of these variables results in non-random patterns of drift. These results are discussed using a multiple-input model of vertical eye-in-head position control.

Adult↗
PubMed1997

A comparison of contrast letter thresholds in unilateral eye enucleated subjects and binocular and monocular control subjects.

We previously reported that unilaterally eye enucleated subjects show superior contrast letter acuity to normally sighted monocular viewing control subjects. We suggested that reorganization of the visual system in the enucleated subjects may compensate for their loss of binocularity. Here we measured contrast letter acuity in normally sighted binocular control subjects and compared these results to previously published results of eye enucleated subjects and monocular viewing control subjects. We found equivalent performance between enucleated subjects and binocular control subjects, suggesting that performance of enucleated subjects might be due to some form of neural summation.

Adolescent↗
PubMed1996

Contrast letter thresholds in the non-affected eye of strabismic and unilateral eye enucleated subjects.

To investigate the effects of visual disruption on contrast letter thresholds of the non-affected eye, subjects with one eye enucleated, strabismic subjects using the non-deviating eye and normal control subjects were asked to identify letters on eye charts and single letter cards which varied in contrast (between 4 and 96%) and size. At all contrast, contrast letter acuity of eye enucleated subjects was superior to both normal control subjects and strabismic subjects. Early onset strabismic subjects (onset < 24 months) showed inferior performance to normal control subjects at all contrasts of 25% and above. Late onset strabismic subjects showed normal performance at all contrasts, except for high contrast single letters, where performance was inferior to normal control subjects. Further, for all subjects groups, performance on letter charts was similar to performance on single letter cards. We conclude that disruption to the visual system caused by eye enucleation or strabismus is not equivalent. These differences may be due to intrinsic differences between the visual systems of eye enucleated subjects and strabismic subjects and/or to the profound differences in deprivation caused by the two conditions.

Adolescent↗
PubMed1996

Learning to look with one eye: the use of head turn by normals and strabismics.

When asked to look through a tube, young children (normal, strabismic, monocularly enucleated) place it between the eyes, while older children turn the head or shut one eye. We videotaped 174 children (normals and strabismics, 2-17 yr of age) and 16 normal adults to find out when and why head turn occurs. In learning to look with one eye, children progressed through a sequence of four responses, categorized by age or amount of head turn. Binocular children use head turn apparently to avoid diplopia, then, most learn to shut one eye. Adults, forced to use the "non-preferred" eye, revert to turning the head.

Adolescent↗
PubMed1995

Alignment ability of strabismic and eye enucleated subjects on the horizontal and oblique meridians.

For normal sighted observers visual performance is often superior on the principal meridians than on the oblique. There has been no clear consensus on whether disruption of the visual system affects performance on orientation sensitivity tasks. Here we compare the abilities of normally sighted subjects tested monocularly, subjects with one eye enucleated and strabismic subjects using the non-deviating eye, in an orientation task. Subjects were asked to align a dot with a bar that was oriented either horizontally or on the oblique. For all groups, alignments were significantly more accurate and precise for the horizontal bar as compared to the oblique bar. Normally sighted subjects were significantly more precise on alignments in the horizontal and oblique planes than strabismic subjects, using the non-deviating eye. Precision for eye enucleated subjects was similar to that of normally sighted subjects. Precision of alignments did not correlate to the age at diagnosis of strabismus or to depth of amblyopia in strabismus. We conclude that for alignment ability, the disruption of visual development produced by enucleation of eye is not equivalent to that produced by strabismus. This could represent an underlying difference in the visual system between these two groups.

Adolescent↗
PubMed1993

The effect of gravity on the resting position of the cat's eye.

We measured rotation (horizontal, vertical and torisonal) and translation (horizontal and vertical) of the paralysed cat's eye in response to 45 degrees steps of orientation presented in a pseudorandom order around the roll and pitch axes (with respect to the horizontal canals). During changes of position of the animal in the roll plane, the eyes rotated towards the lowest part of the orbit (left with left ear down; top when the cat was upside down, etc.) by an average of 0.55 degree. Changing orientation in the pitch plane evoked vertical rotations of +/- 1.42 degrees (upwards eye movement during forwards head pitch) and torsional rotations of +/- 1.3 degrees. All these rotations taken together suggest that the centre of mass is in front of, below and temporal to the centre of rotation. The eyes translated temporally (thus separating by 0.72 mm) during forward pitching and there was a small vertical displacement (0.23 mm) when the animal was upside down. These findings are discussed with respect to a possible role of the extraocular proprioception system.

Animals↗
PubMed1993

Egocenter location in children with strabismus: in the median plane and unchanged by surgery.

PURPOSE: Previous studies have shown that there are spatial localization shifts after horizontal strabismus surgery when a patient performs an open-loop pointing task. After monocular enucleation, an adult will also show a shift in the pointing response. Other studies have shown that in children who underwent enucleation, the egocenter location shifts toward the remaining eye. Is the pointing shift after surgery in children with strabismus the result of a shift in egocenter location? METHODS: Using a modified Roelofs' method for measuring the egocenter, eight children were tested before and after horizontal strabismus surgery to see if there were any shifts in egocenter location. One control group consisted of six children undergoing surgery for correction of vertical strabismus in which the horizontal muscles would be unaltered. RESULTS: Presurgery measurements of egocenter location in the people with strabismus were the same as those found in the other control group of 12 normal children. Postsurgical measurements of eye position showed horizontal rotations of 14.5 degrees for the horizontal group and 2.4 degrees for the vertical group. Egocenter measurements showed no postoperative shift for either strabismus group. CONCLUSIONS: Thus, the pointing shift seen in the previous studies is not from a shifting egocenter location but from a change in the registered position of the eye in the orbit.

Child↗
PubMed1991

The development of optokinetic nystagmus in strabismic and monocularly enucleated subjects.

Assymmetries of monocular optokinetic nystagmus (OKN) following anomalous visual experience are thought to be due to disruption at the cortical level. Visual disruption usually results from eye suture (in animals), unilateral dense and central cataracts or strabismus (in humans). Many form-deprived animals and humans frequently show a residual strabismus after lid opening (animals) or cataract extraction and optical correction (humans). We wanted to determine whether strabismus was unique in causing monocular asymmetries of OKN. Two independent observers rated eye movement videotapes of 20 normal subjects, the non-deviating eye of 25 unilateral strabismic subjects and 29 unilaterally eye-enucleated subjects, who were watching either a nasally directed square wave grating, a temporally directed square wave grating, or a blank field. Observers rated the proportion of trials where OKN occurred, the duration of OKN in each trial and the number of beats of OKN within each trial. Monocular OKN was symmetrical in normal subjects for the proportion and duration measures, but half the normal group showed small but significant asymmetries for the beats measure. Subjects in both enucleate and strabismic groups showed asymmetries of OKN favouring nasally directed stimulation, but only the early onset strabismics (as a group) showed asymmetries that were significantly greater (P less than 0.05) than the normal group. Asymmetry scores correlated significantly with age of diagnosis of strabismus for the strabismic group but not with age of enucleation for the enucleate group. The results are discussed in terms of binocular competition.

Adolescent↗
PubMed1991

Motion parallax judgements of depth as a function of the direction and type of head movement.

We compared the relative effectiveness of rotating or translating the head, either horizontally or vertically, on the perception of depth resulting from motion parallax. Using Rogers and Graham's (1979) paradigm, we yoked the movement of random dots on a screen to movements of the head, simulating a corrugated surface. In two experiments, subjects nulled the apparent depth or motion seen in the display. Horizontal head movements yielded the most precise depth judgements, irrespective of whether the head translated or rotated. Motion thresholds were higher than those for depth and were independent of direction of head movement. In a third experiment, suprathreshold stimuli that simulated differing amounts of depth were used, and the subjects' perception of depth was virtually the same for all types and directions of head movement. In our stimulus situation, rotating or translating the head either vertically or horizontally produced motion parallax cues for depth that were equally effective. Our results also showed that, within a range, retinal image motion from head movement is converted into a depth signal and that above that range location constancy breaks down and motion is seen.

Adult↗
PubMed1990

Monocular stereopsis with and without head movement.

Random dots moving with various velocity gradients were presented to observers; the motion was yoked to head movement in one condition and to no head movement in another. In Experiment 1, 12 observers were shown motion gradients with sine, triangle, sawtooth, and square waveforms with amplitudes (equivalent disparities) of 12' and 1 degrees 53'. In Experiment 2, 48 observers were shown only the sinewave or square-wave gradient of 1 degrees 53' disparity either with or without head movement so that the observers' expectation to see depth in one condition did not transfer to another. The main findings were: (1) with 12' disparity, the head-movement condition produced perceived depth but almost no perceived motion, whereas the no-head-movement condition produced both perceived depth and perceived motion; (2) with 1 degrees 53' disparity, both conditions produced perceived depth and perceived motion; and (3) when the expectation to see depth was removed, the no-head-movement condition with the square-wave gradient produced no perceived depth, only motion. We suggest that monocular stereopsis with head movement can be achieved without perception of motion but monocular stereopsis without head movement requires perception of motion.

Attention↗
PubMed1988

Egocenter location in children enucleated at an early age.

In normal binocular vision the origin of judgments of visual direction is the egocenter located on the median plane of the head, midway between the two eyes. For children enucleated at an early age there is abrupt cessation of binocular input to the visual cortex. We evaluated the effect of early removal of one eye on the location of the egocenter, comparing the results in enucleated children to normal binocular children tested monocularly. We found a significant shift of the egocenter towards the remaining eye of the enucleates that was unrelated to the age at enucleation. At least up to 4 years of age, egocenter location is plastic and can be modified by the complete monocularity imposed by enucleation.

Adolescent↗