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Biomedical subjects

R S Harwerth

Publications and source records attributed to R S Harwerth.

At least 73 records · Page 4Linked to original sources
PubMed1984

Effects of enucleation of the nondeprived eye on stimulus deprivation amblyopia in monkeys.

The effects of enucleation of the nondeprived eye on the visual function of the deprived eye were studied in two rhesus monkeys reared with long-term lid suture. The lids of one eye of each monkey were surgically fused at the age of approximately 1 month. The lids were opened at ages 19 months and 22 months, and the nondeprived eyes were enucleated at age 57 months. Three measures of visual function (spatial modulation sensitivity, temporal modulation sensitivity, and increment-threshold spectral sensitivity) were determined for the nondeprived and deprived eyes before enucleation and for the deprived eyes during a 9-month period following enucleation. Neither the spatial nor temporal modulation sensitivity measurements showed significant recovery of visual function. The postenucleation spectral sensitivity data showed some recovery of sensitivity over the long wavelength region of the spectrum during the first 3 months, but there was no further recovery over the next 6 months. Therefore, the results of the experiments show that enucleation of the nondeprived eye of monkeys with severe stimulus deprivation amblyopia does not result in a significant functional improvement of the deprived eye.

Accommodation, Ocular↗
PubMed1984

Permanent alterations in muscarinic receptors and pupil size produced by chronic atropinization in kittens.

Chronic mydriasis was induced in six kittens (four monocular, two binocular) and two adult cats (both monocular) by the daily topical application of atropine. Both the kittens and the adult cats were atropinized for a 13-week period with the treatment regimen beginning at the time of eye opening for the kittens. Pupil size measurements, obtained 1 year after the atropinization were discontinued, revealed that, although the pupils of the adult cats were normal, the pupils of the kittens' treated eyes were consistently smaller than pupils in control eyes. The status of the muscarinic receptors in the kittens' irides was investigated using 3H-QNB binding assays. In comparison with iris muscle homogenates from the control eyes, those from the treated eyes demonstrated an eightfold increase in the number of receptor binding sites. The results indicate that pupil size can be altered permanently by chronic mydriasis initiated early in the life of a kitten and that the permanent change in pupil size may result, in part, from a type of permanent supersensitivity response in the muscle following chronic blockade of muscarinic transmission by atropine.

Age Factors↗
PubMed1984

Stereoblind monkeys have few binocular neurons.

Infant monkeys wore prisms before their eyes, lost binocular neurons from their visual cortex, and were stereoblind to dynamic random dot stereograms. Three years later, the authors recorded from 880 neurons of the V1 and V2 visual cortex and found only 22% binocular neurons as compared with 81% for normal monkeys. These results demonstrate, for the first time in the same subjects, the strong association between cortical binocular neurons and primate stereopsis; show that congenital binocular neurons, once lost, do not recover even with extensive binocular visual experience; and stress the vulnerability of the primate binocular system to abnormal early visual experiences.

Age Factors↗
PubMed1983

Oblique effects, vertical effects and meridional amblyopia in monkeys.

Orientation anisotropies were investigated for monkeys with normal visual acuity and for monkeys with experimentally induced amblyopia. It was found that the majority of control monkeys showed a normal oblique effect if any existing refractive errors were carefully corrected, but a few of the control monkeys had a meridional amblyopia, i.e., an orientation anisotropy in which the grating orientation for the greatest and lowest contrast sensitivities were correlated with the principal meridians of an astigmatic refractive error even when the refractive error was corrected. For monkeys with strabismic amblyopia caused by a surgically induced divergent strabismus, the orientation anisotropies showed a vertical effect in which contrast sensitivity was lower for vertically oriented gratings than for horizontally oriented gratings. However, monkeys with the same degree of amblyopia resulting from experimental procedures that did not involve a misalignment of the visual axes showed orientation anisotropies that corresponded to the usual oblique effect.

Amblyopia↗
PubMed1983

Behavioral studies on the effect of abnormal early visual experience in monkeys: spatial modulation sensitivity.

Spatial modulation sensitivity functions have been investigated by behavioral methods in two monkeys reared with normal visual experience and 12 monkeys reared with abnormal, early visual experience. Experimental treatments were initiated when the animals were approximately one month of age. Two monkeys were each treated with one of the following procedures: (1) long-term monocular lid suture, (2) short-term monocular lid suture, (3) surgically induced esotropia, (4) surgically induced exotropia, (5) optical dissociation of binocular vision with ophthalmic prisms, or (6) chronic monocular cycloplegia. The results of the studies showed a severe loss of contrast sensitivity of the treated eyes compared to the control eyes for monkeys reared with monocular lid suture or surgically induced esotropia. Surgically induced exotropia resulted in a moderate reduction in sensitivity of the deviated eye while optical dissociation resulted in a mild reduction in sensitivity of one eye compared to the other. One of the two monkeys reared for seven months with chronic monocular cycloplegia had a relative reduction in contrast sensitivity of the treated eye, but the other monkey had equal sensitivities in the two eyes. However, binocular summation experiments showed that even though the relative difference between the monocular sensitivities was small or absent for the monkeys reared with optical dissociation or chronic monocular cycloplegia, none of them demonstrated binocular vision in these experiments.

Amblyopia↗
PubMed1983

Behavioral studies on the effect of abnormal early visual experience in monkeys: temporal modulation sensitivity.

Temporal modulation sensitivity functions were investigated by behavioral methods in two monkeys reared with normal visual experience and 12 monkeys reared with abnormal early visual experience. Experimental treatments were initiated when the animals were approximately one month of age. Two monkeys were each treated with one of the following procedures: (1) long-term monocular lid suture, (2) short-term monocular lid suture, (3) surgically induced esotropia, (4) surgically induced exotropia, (5) optical dissociation of binocular vision with ophthalmic prisms, or (6) chronic monocular cycloplegia. The temporal modulation sensitivity functions for uniform field flicker for both eyes of the control subjects and for the untreated eyes of the experimental subjects were similar to functions for humans measured on the same apparatus using the same behavioral procedures. All eight of the monkeys preconditioned by lid suture or surgically induced strabismus showed reduced sensitivity at all temporal frequencies with the difference between the experimental and control eyes being larger for the high than low temporal frequencies. The monkeys reared with optical dissociation of binocular vision or chronic monocular cycloplegia showed equal temporal modulation sensitivities of the two eyes, but failed to show binocular summation. It was concluded from these studies that abnormal early visual experience in monkeys results in deficiencies in the processing of both spatial and temporal information, but the differences between the treated and untreated eyes were usually greater in the spatial domain than the temporal domain.

Amblyopia↗
PubMed1983

Effects of chronic atropinization on visual acuity in kittens.

Atropine was instilled daily from the time of eye-opening until 14 weeks of age into either one or both eyes of developing kittens. Following a 4 week recovery period, grating visual acuity was determined using behavioral techniques under both monocular and binocular viewing conditions. The monocularly treated kittens behaviorally demonstrated an amblyopia in the treated eye and an absence of binocular summation. In contrast, the binocularly treated kittens appeared to show normal visual acuity in both eyes and their performance improved during binocular viewing conditions. Single-unit recordings in striate cortex indicated that binocular atropinization did not alter cortical binocularity, however, monocular atropinization resulted in a decrease in the proportion of binocularly excited neurons and a shift in ocular dominance to the untreated eye.

Amblyopia↗
PubMed1983

Psychophysical studies on the binocular processes of amblyopes.

It has frequently been assumed that humans with abnormal binocular vision resulting from amblyopia or strabismus lack binocular cortical neurons. From this assumption, it would be predicted that amblyopes would fail to show binocular interactions on any psychophysical tasks. This paper describes some recent psychophysical experiments investigating the binocular processes of amblyopes. The results of these experiments have shown that most humans with abnormal binocular vision fail to show binocular interactions for psychophysical tasks such as stereopsis or binocular summation, but show partially normal binocular interactions for interocular transfer of visual aftereffects and show normal interactions for dichoptic masking with grating stimuli.

Amblyopia↗
PubMed1983

Binocular neurons and binocular function in monkeys and children.

Electrophysiologic studies have shown that binocular neurons of the striate cortex of monkeys are irreversibly lost when the visual axes of the eyes are optically dissociated during the first weeks of life. The present study was a behavioral investigation of monkeys reared with optical dissociation. After brief periods of experimental strabismus, the monkeys showed poor binocular summation performance and were unable to see random dot stereograms even after two years of post-treatment normal binocular vision. These monkeys' performance on the stereopsis task was virtually identical to the stereoperformance of clinically diagnosed stereoblind children.

Adolescent↗
PubMed1982

Color vision is altered during the suppression phase of binocular rivalry.

Increment-threshold spectral sensitivity functions were determined during the dominance and suppression phases of binocular rivalry. The shapes of the functions obtained during the dominance phase exhibited three maxima at approximately 440, 530, and 610 nanometers and resembled functions obtained for nonrivalrous control conditions. However, the functions measured during suppression had a single broad peak near 555 nanometers and were adequately described by functions measured with flicker methods during nonrivalrous conditions. The results indicate that binocular rivalry differentially attenuates opponent-color information relative to achromatic information.

Color Perception↗
PubMed1982

Psychophysical mechanisms in humans with amblyopia.

This study shows that the loss of contrast sensitivity in the amblyopic eye does not result from abnormal spatial frequency selective channels. Knowledge of the sine-wave sensitivity of the amblyopic eye may allow accurate predictions of the detection threshold for more complex stimuli. More effective amblyopia treatment strategies may be designed when the amblyope's sensitivity to spatial contrast and relative phase are better understood.

Amblyopia↗
PubMed1982

Optically induced anisometropia in kittens.

Anisometropia was simulated in 11 kittens during the critical period of visual system development by securing a high-powered minus lens in front of one eye. Behavioral determinations of monocular grating acuity indicated that the induced refractive error resulted in severe amblyopia in the defocused eye. Microelectrode recordings in striate cortex revealed that the deficits in visual acuity were paralleled by a decrease in binocularly innervated neurons and a marked shift in ocular dominance toward the nondeprived eye. "Position of paralysis" estimates revealed that all the anisometropic kittens exhibited anomalous interocular alignments that were indicative of estropia. There was also a significant reduction in the cross-sectional areas of dorsal lateral geniculate nucleus (LGNd) neurons in laminae innervated by the deprived eye. A 6 week period of binocular recovery initiated when three of the anisometropic kittens were approximately 16 weeks of age resulted in a partial recovery of visual acuity; however, there was little or no evidence for recovery of cortical binocularity, cortical ocular dominance, LGNd neuron cell size, or interocular alignment. In general the visual system alterations produced by the induced anisometropia appear to be qualitatively similar to the anomalies associated with prolonged unilateral lid suture.

Animals↗
PubMed1982

Glenn Fry Award Lecture: behavioral studies of amblyopia in monkeys.

Many of the current concepts on the mechanisms of binocular vision and amblyopia have been developed from physiological studies on animals. It is important to compare psychophysical data from these species with human data in order to provide a more direct link between the physiology and behavior of humans. This paper describes behavioral experiments on rhesus monkeys with normal binocular vision and monkeys with experimental amblyopia. The visual functions investigated were stereopsis, fusional vergence ranges, spatial contrast sensitivity, and increment-threshold spectral sensitivity. The comparison of data from human observers with those of the monkeys shows remarkable agreement. The monkey is useful as a surrogate for experiments that are either impossible or impractical to conduct on humans, and the data may be applied to the human population.

Amblyopia↗
PubMed1981

Edge sensitive mechanisms in humans with abnormal visual experience.

Detection of broadband, aperiodic stimuli (edges) was investigated in normal observers, and in observers with abnormal visual experience which resulted in amblyopia. The spatial properties of the mechanisms used to detect an edge were investigated by a method of subthreshold addition. The method involved the determination of the threshold contrast for detecting an edge in the presence of a subthreshold line at various distances from the edge. In normal eyes, the one dimensional sensitivity profile of the edge detecting mechanism was: (1) approximately antisymmetric, (2) very localized, with sensitivity changes restricted to +/- 6'--8' on either side of the edge, and (3) phase dependent, showing an abrupt change in sign between +/- 1.5'. The sensitivity profiles of the amblyopic eyes were also approximately antisymmetric and showed the same steep rate of change from plus to minus as the fellow (nonamblyopic) eyes. However, in every case, the spatial extent of the profile was much broader than that of the nonamblyopic eyes. In normal eyes, the narrowest edge sensitivity profile was associated with the fovea; however, in two amblyopes with eccentric fixation, the narrowest edge sensitivity profile coincided with the locus of eccentric fixation. Moreover, the grating sensitivity function of the edge detecting mechanism of the amblyopic eye was similar to that of the non-amblyopic eye, but was shifted toward lower spatial frequencies. Control experiments show that these results are not accounted for on the basis of optics, eccentric fixation, or abnormal eye movements. The findings are discussed in terms of current models for the detection of aperiodic stimuli, and in the context of animal models of amblyopia.

Adult↗
PubMed1980

Binocular interactions in normal and anomalous binocular vision.

Binocular interactions for grating patterns were investigated in humans with normal binocular vision and in humans with abnormal binocular visual experience due to strabismus and/or amblyopia via 1) comparison of monocular and binocular contrast thresholds; 2) interocular transfer of the threshold elevation aftereffect; and 3) dichoptic masking. Whereas the normal observers showed improved binocular over monocular contrast sensitivity (i.e., binocular summation) and substantial interocular transfer of the threshold elevation aftereffect, the abnormal observers showed an absence of binocular summation and no significant interocular transfer. The dichoptic masking experiments showed that a suprathreshold masking grating presented to one eye elevated the contrast threshold for gratings presented to the fellow eye, within a narrow range of spatial frequencies (about 1 octave wide at half height) and orientations, centered about the spatial frequency and orientation of the mask. The magnitude and bandwidth of this masking effect was similar in subjects with normal and abnormal binocular vision, occurring even when the masking grating was presented to the amblyopic eye. These effects depend upon the contrast of the masking grating. In individuals with normal binocular vision, a grating with subthreshold contrast presented to one eye reduces the contrast threshold for detection of gratings of similar spatial frequency and orientation presented to the fellow eye. No such subthreshold summation is evident in the amblyopic observers. We conclude that while strabismus and/or amblyopia disrupted the normal excitatory interactions between the two eyes, cortical inhibitory binocular connections were not disrupted.

Adult↗