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Biomedical subjects

R E Manny

Publications and source records attributed to R E Manny.

36 records · Page 2Linked to original sources
PubMed1986

Visual acuity of the preschool child: a review.

The need for visual acuity assessment in preschool children has long been recognized, yet there are no standardized visual acuity norms or screening criteria. This report reviews the literature on distance visual acuity in the preschool child. The areas of review include: methods of assessment of visual acuity; visual acuity norms obtained with these tests; reasons for the variations in reported visual acuity norms; variations in referral criteria for vision screenings; testability reported for various visual acuity tests; and important design principles and recommendations for preschool visual acuity tests. It is concluded that a well designed preschool visual acuity test should consist of high contrast Snellen optotypes without directional components that progress in 0.1 log steps down to a level of 6/3. To improve testability, a matching or forced choice response should be used. Of the tests that have been standardized, STY-CAR (Sheridan-Gardiner) comes closest to meeting these criteria.

Child↗
PubMed1985

A three alternative tracking paradigm to measure vernier acuity of older infants.

Vernier acuity was measured in infants 1 to 14 months of age using a dynamic three alternative tracking paradigm. The location of the vernier offset would move randomly to one of three screen locations. An observer, unaware of the stimulus location, viewed the infant from behind a screen and guessed the position of the vernier offset. The magnitude of the vernier offset was controlled by a staircase and the results were analyzed using a broken line psychometric function. These thresholds were compared to thresholds obtained from the same infants during the same session with a two alternative forced choice preferential looking paradigm. Differences in the results of these two procedures and those reported previously in the literature are discussed in terms of the differences in the nature of the visual stimuli, one containing motion and one without motion.

Aging↗
PubMed1985

Selectivity of the evoked potential for vernier offset.

Hyperacuity thresholds of a few arc seconds can be achieved psychophysically for a variety of spatial localization tasks. The present experiments show that evoked potentials can be elicited in response to the introduction of vernier offsets, but not by the introduction of other cues to hyperacuity such as bisection or relative pattern motion, although each of these cues is equally salient psychophysically. Moreover, vernier acuity measurements and the evoked potentials elicited in response to vernier offsets are strongly degraded by the introduction of flanking stimuli 2-4 min from the vernier target. This suggests that the hyperacuity VEP is a cortical correlate of a very specific type of hyperacuity, that produced by vernier offsets (colinearity failure).

Adult↗
PubMed1985

The relationship between binocular rivalry and strabismic suppression.

Increment-threshold spectral sensitivity functions were determined for normal observers during binocular rivalry and for esotropic observers during strabismic suppression and under viewing conditions that normally induce binocular rivalry. Depending on the spatial and temporal properties of the test stimulus, the normal observers exhibited a wavelength-specific loss in sensitivity during the suppression phase of rivalry, which suggests that binocular rivalry differentially attenuates the sensitivity of the chromatic mechanisms relative to the luminance mechanisms. In contrast, regardless of the test stimulus dimensions, the esotropic observers did not manifest a wavelength-specific loss in sensitivity either during strabismic suppression or under conditions that normally induce binocular rivalry. The different patterns of suppression shown by the normal and esotropic subjects suggest that strabismic observers do not demonstrate normal binocular rivalry, and that strabismic suppression and normal binocular rivalry suppression are mediated by different neural mechanisms.

Adult↗
PubMed1984

The development of vernier acuity in infants.

Vernier and grating acuity were measured in infants up to 6 months of age using a two-alternative forced-choice preferential looking technique. Vernier resolution was measured using a horizontal vernier grating. The grating was presented on half of the screen while the other half contained horizontal lines which were continuous with the vernier grating. Movement artifacts were eliminated by making both halves of the display move as the offsets were introduced in half of the display field. Vernier acuity, like grating acuity, improved about 3 octaves over the first 6 months of life. Moreover, the vernier resolution of infants, as of adults, was better than grating resolution.

Child Development↗
PubMed1983

Clinical assessment of visual acuity in human infants.

Electrophysiological and fixation preference techniques have been used in the laboratory to assess numerous visual functions in infants. However, the laboratory situation is considerably different from the clinical setting. A modification of the procedures developed in the laboratory is required before they may be applied to the routine clinical examination of infants. This paper reviews these issues.

Child, Preschool↗
PubMed1982

The visually evoked potential in humans with amblyopia: pseudorandom modulation of uniform field and sine-wave gratings.

The visually evoked potential was recorded in response to pseudorandom modulation of a uniform field and sine-wave gratings in humans with naturally occurring amblyopia. Analysis in the frequency domain showed similar temporal tuning when the nonamblyopic and amblyopic eye were stimulated with a uniform field and with spatial stimuli. Although most observers showed some reduction in the cortical response to stimulation of the amblyopic eye with uniform field modulation, all observers showed reductions in the response obtained for stimulation of the amblyopic eye with spatial stimuli. This decrease in the cortical response to stimulation of the amblyopic eye for sine-wave gratings was present at either the low and middle temporal frequencies or over the range of temporal frequencies tested, and was greater than that observed in those amblyopes who also showed reductions with uniform field modulation. Latency measures in the time domain showed increases in the response of the early components when the amblyopic eye was stimulated with a uniform field and with sine-wave gratings above 2 c/deg. These electrophysiological results confirm the results obtained psychophysically which suggest that although amblyopia is primarily a spatial anomaly, the response is influenced by the temporal attributes of the stimulus as well.

Adolescent↗
PubMed1982

Binocular interactions in normal and anomalous binocular vision: effects of flicker.

Temporal modulation thresholds were determined for monocular viewing and for binocular viewing of stimuli presented in phase or in counterphase to each eye of observers with normal binocular vision and those lacking stereopsis. The results showed that in individuals with normal binocular vision sensitivity was much greater for in-phase than for counterphase stimulation at low temporal frequencies, but that this superiority declined at higher temporal frequencies. Averaged across frequencies, binocular sensitivity for in-phase stimulation was 40-50% higher than monocular sensitivity. In contrast, in the observers lacking stereopsis the ratios of binocular in-phase/monocular sensitivity averaged 1.02, and there were no significant differences in sensitivity to in-phase and counterphase stimulation. This failure of binocular integration at threshold does not result from differences in transmission time between the 2 eyes. However, while individuals lacking stereopsis showed an absence of binocular interaction for uniform-field flicker at threshold, they showed suprathreshold dichoptic temporal frequency masking which was similar to that found in normal persons.

Adult↗
PubMed1982

Psychophysical investigations of the temporal modulation sensitivity function in amblyopia: uniform field flicker.

The temporal modulation sensitivity function was studied in eight strabismic and/or anisometropic amblyopes and in two subjects with amblyopia resulting from monocular stimulus deprivation (cataract and ptosis). Half of the strabismic/anisometropic amblyopes showed a reduction in the sensitivity of the amblyopic eye. These differences were more marked at low and middle temporal frequencies. Two strabismic/anisometropic observers showed little difference in sensitivity between the two eyes, but in the remaining two observers the amblyopic eye was slightly more sensitive to low-frequency modulation than was the nonamblyopic eye. Four of the strabismic/anisometropic amblyopes also showed a small (5% to 10%) but statistically significant difference in the critical fusion frequency, with the sensitivity of the amblyopic eye being reduced. These differences in sensitivity were not related to the visual acuity loss. However, all differences in sensitivity between the two eyes were reduced or eliminated when the mean luminance of the test field was decreased by 2 log units form 32 to 0.32 cd/m2, or with suprathreshold stimulation. One of the two stimulus-deprivation amblyopes showed a decrease in sensitivity to low and middle temporal modulation frequencies similar to that found in four of in sensitivity to low and middle temporal modulation frequencies similar to similar to that found in four of the strabismic/anisometropic amblyopes, and the other observer showed a marked decrease in sensitivity at all temporal frequencies. The losses in temporal resolution of the amblyopic eye in both strabismic/anisometropic and stimulus-deprivation amblyopia are small in comparison with those reported in the spatial domain.

Adolescent↗
PubMed1982

Psychophysical investigations of the temporal modulation sensitivity function in amblyopia: spatiotemporal interactions.

Temporal modulation sensitivity functions were measured in response to counterphase sine-wave gratings of various spatial frequencies in seven strabismic and/or anisometropic amblyopes and in two stimulus-deprivation amblyopes. Both movement/flicker and pattern detection thresholds were determined. Strabismic and/or anisometropic amblyopes showed reduced sensitivity for movement/flicker and pattern detection in the amblyopic eyes, which were dependent on both the spatial and temporal frequencies of the stimulus and the detection criterion. At medium and high spatial frequencies, substantial reductions in movement/flicker detection were present, which were generally more marked for low temporal modulation frequencies. Reductions in pattern sensitivity were greater at the higher spatial frequencies, although some amblyopes showed losses in sensitivity at low spatial frequencies as well. The losses observed in the spatiotemporal transfer function of the amblyopic eyes were greater than those found with unstructured stimuli (uniform field flicker) and were not eliminated under reduced luminance. In subjects with amblyopia caused by stimulus deprivation, losses in spatiotemporal contrast sensitivity were either invariant across temporal frequencies or increased at higher rates of temporal modulations.

Amblyopia↗
PubMed1981

ERG off-effects produced by short duration stimuli.

Variable duration square wave pulses of 633-nm light were used to produce electroretinograms (ERG's) in a human subject. When the stimuli were presented on a white light background, the records obtained for stimulus durations greater than 70 msec showed a clearly separated off-response while those of shorter durations did not. By subtracting a common "on-effect" from the ERG's produced by short duration stimuli, the previously unseen off-effect was isolated from records produced by stimulus pulses as short as 5 msec. It appears that the marked increase in b-wave amplitude associated with these short duration stimuli can be attributed to an interaction between "on" and "off" components of the ERG.

Computers↗
PubMed1980

Monocular vergence movements produced by external visual feedback.

An external visual feedback procedure was used by three subjects with normal binocular vision to produce monocular lateral vergence (duction) movements. Feedback was provided by monitoring eye position with an alternating magnetic field system and by displaying the position of the monitored eye to the subject on an oscilloscope screen. Each subject was able to produce both unilateral abduction and adduction. For one subject, phorias were measured prior to several of the abduction feedback sessions, and an increase in exophoria and a decrease in the accommodative covergence/accommodation ratio was observed over the preexperimental measurement.

Accommodation, Ocular↗
PubMed1979

Suprathreshold spatial frequency detection and binocular interaction in strabismic and anisometropic amblyopia.

We have investigated suprathreshold contrast sensitivity and binocular interactions in strabismic and anisometropic amblyopes using a reaction time paradigm. For every spatial frequency, reaction time increased as the grating contrast decreased. At all spatial frequencies and contrast values the reaction times using the amblyopic eye were prolonged compared to the nonamblyopic eye, but most markedly at high spatial frequencies. In the middle range of spatial frequencies, the contrast vs. reaction time function for the nonamblyopic eyes was biphasic, suggesting that two separate mechanisms detect gratings at high and low contrast levels. These functions in deep amblyopia were monotonic, and in shallow amblyopia the break in the functions was present but shifted to lower contrast levels. Binocular interaction experiments showed that binocular summation was absent at all contrast levels, but binocular occlusion was evident at high contrast levels for amblyopic observers.

Adolescent↗
PubMedDate not supplied

Electrophysiological correlates of vernier and relative motion mechanisms in human visual cortex.

Vernier onset/offset thresholds were measured both psychophysically and with the steady-state VEP by introducing a series of horizontal breaks in a vertical square-wave luminance grating. Several diagnostic tests indicated that the first harmonic component of the evoked response generated by periodic modulation of offset gratings taps mechanisms that encode the relative position of spatial features. In the first test, a first harmonic component was only found with targets that contained transitions between collinear and noncollinear states. VEP vernier onset/offset thresholds obtained with foveal viewing were in the range of 15-22 arc sec. Control experiments with transitions between symmetrical, noncollinear patterns (relative motion) did not produce first harmonic components, nor did full-field motion of a collinear grating. A second series of experiments showed that VEP thresholds based on the first harmonic component of the vernier onset/offset response had an eccentricity dependence that was very similar to that found in a psychophysical discrimination task that required a left/right position judgment (vernier acuity). Other recordings showed that the first harmonic of the vernier onset/offset VEP was degraded by the introduction of a gap between stimulus elements, as is the displacement threshold. The vernier onset/offset target also produced a second harmonic component that was virtually identical to the one produced by a relative motion stimulus. Displacement thresholds based on these second harmonic components showed a more gradual decline with retinal eccentricity than did the first harmonic component elicited by vernier offsets. The second harmonic of the vernier onset/offset VEP was relatively unaffected by the introduction of gaps between the stimulus elements. The first and second harmonic components of the vernier onset/offset VEP thus tap different mechanisms, both of which support displacement thresholds that are finer than the resolution limits set by the spacing of the photoreceptors (hyperacuity).

Evoked Potentials, Visual↗
PubMedDate not supplied

Electrophysiological correlates of hyperacuity in the human visual cortex.

The human visual system is capable of detecting a vernier misalignment with extraordinary accuracy. Since this remarkable precision in spatial localization is better than can be naively predicted by simple optical or anatomical considerations it has been termed a hyperacuity. So far no single neurone model seems capable of accounting for hyperacuity, and the retinal image might require reconstitution in a finer grained from in the visual cortex. We report here an electrophysiological correlate of hyperacuity recorded from the human visual cortex. The amplitude of the visually evoked potentials (v.e.ps) elicited by the appearance of a vernier offset varied systematically with the magnitude of the offset. Extrapolation of the function relating v.e.p. amplitude and log offset to zero voltage resulted in an electrophysiological estimate of vernier acuity that was similar to the observer's psychophysical threshold.

Electroencephalography↗
PubMedDate not supplied

Testing stereopsis in the preschool child: is it clinically useful?

The evaluation of stereoacuity should provide an unambiguous assessment of binocular function in infants and young children. Unfortunately, clinical measures of stereopsis in these young patients often result in stereotheresholds poorer than the criteria suggested to differentiate normal from anomalous binocular vision. Thus, two experiments were conducted to determine whether the large stereothresholds frequently demonstrated on tests designed for young children are diagnostic of normal binocular function in preschool children. The first experiment investigated the salience of the monocular cues in the Lang and Frisby stereotests in normal preschool children (2 to 5 years old). None of the children who passed either the Frisby or the Lang stereotest under binocular conditions were able to pass either test monocularly, even after passing the test binocularly. In the second experiment, preschool children with abnormal binocular vision were tested with the Lang and Frisby stereotests to determine if large disparities (730 to 800 seconds of arc [arcsec]) could be passed without normal binocular vision. None of the children with strabismus passed either stereotest. However, two children with anisometropia passed the Frisby test and one of these children also passed the Lang test. These results suggest that in the absence of other clinical findings to the contrary, the demonstration of gross stereopsis with either the Frisby (730 arcsec) or Lang (733 or 800 arcsec) test in the preschool child implies normal binocular function. Thus, clinical tests of stereopsis for infants and preschool children, like those used routinely for adults, can provide evidence of binocular function without approaching stereothreshold.

Amblyopia↗