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Biomedical subjects

R S Harwerth

Publications and source records attributed to R S Harwerth.

At least 91 records · Page 5Linked to original sources
PubMed1980

Ocular dominance, eye alignment and visual acuity in kittens reared with an optically induced squint.

A horizontal concomitant strabismus produced optically in kittens with prisms caused a decrease in the proportion of binocularly excitable striate neurons with approximately equal percentages of neurons being driven by each eye. In addition, preventing fusion with prisms resulted in alterations in interocular alignment and in some cases a mild strabismic amblyopia. The changes in ocular dominance were dependent on the amount and direction of the prism induced deviation; however, regardless of the type of prisms worn, the kittens which demonstrated interocular misalignments were esotropic.

Animals↗
PubMed1980

Meridional amblyopia in monkeys.

Contrast sensitivity as a function of the orientation of a grating stimulus was determined by behavioral methods for four rhesus monkeys. Two of the monkeys had been reared with normal binocular experience, had spherical refractive errors, and showed a normal oblique effect. The other two monkeys which had been reared with one eyelid sutured (which was still sutured during these experiments), showed astigmatic refractive errors in the non-deprived eye and grating contrast sensitivity as a function of orientation that was correlated with the principal meridians of their astigmatism. Control experiments showed that the meridional amblyopia was not due to an uncorrected refractive error. Reaction time measures of contrast sensitivity for suprathreshold grating patterns showed that meridional amblyopia was not present for high contrast gratings.

Animals↗
PubMed1980

Stereopsis and fixation disparity following prolonged monocular occlusion.

The effects of 12 days of continuous monocular occlusion on the stereoscopic acuity and the magnitude of the fixation disparity associated with a given amount of prism-forced vergence were investigated in six adult subjects with normal binocular vision. After the period of occlusion, all six subjects were able to perceive stereopsis, although four of the six subjects demonstrated a slight but reversible elevation in stereothresholds. The general shape of the fixation disparity curve for a given individual was not altered by occlusion, but changes in the magnitude of the fixation disparity were observed for some subjects.

Adult↗
PubMed1980

Contrast sensitivity in amblyopia due to stimulus deprivation.

Contrast sensitivity functions for sinusoidal gratings of varying spatial frequency and stimulus duration were determined for both eyes of 2 patients with amblyopia due to early occlusion and lid closure. The amblyopic eyes showed reduced contrast sensitivity over a wide range of spatial frequencies and stimulus durations, and the temporal integration time of the amblyopic eye was increased by comparison with the non-amblyopic eye at high spatial frequencies. When the gratings were flickered at 10 Hz the sensitivity for both flicker and pattern detection was reduced in the amblyopic eye over the entire spatial frequency range. Abnormal flicker perception by the amblyopic eyes was also evident in the reduced photopic luminosity functions of these patients.

Adult↗
PubMed1979

Humans deprived of normal binocular vision have binocular interactions tuned to size and orientation.

A suprathreshold grating presented to one eye elevated the threshold for the discrimination of gratings similar in size and orientation presented to the fellow eye. The magnitude and stimulus specificity of these binocular interactions in human observers with normal bioncular vision were similar to those in observers deprived of normal binocular visual experience; however, the latter showed a failure of binocular summation at threshold or subthreshold contract levels. Whereas strabismus or amblyopia disrupted the normal excitatory interactions between the two eyes, cortical inhibitory binocular connections seem not to have been disrupted.

Amblyopia↗
PubMed1979

Orientation anisotropy of visual stimuli in rhesus monkey: a behavior study.

The contrast sensitivity of the rhesus monkey was tested, according to a modified reaction-time paradigm, for sine-wave grating targets at different orientations. The monkey possesses an oblique effect slightly larger than that of humans. A reaction time analysis showed the oblique effect to be a suprathreshold as well as a threshold phenomenon. The presence of this effect further strengthens the use of the monkey as a model for the human visual system.

Animals↗
PubMed1979

Binocularity in kittens reared with optically induced squint.

The effects of conflicting visual images were studied without the confounding influences of oculomotor abnormalities: strabismus was simulated by rearing kittens with ophthalmic prisms before the eyes. After the animals had matured, the response properties of neurons in the visual cortex were studied. The proportion of binocularly excited neurons decreased; however, the extent of the ocular dominance alterations was related to the amount and direction of the prism-induced deviation.

Action Potentials↗
PubMed1979

Fusional vergence ranges of the monkey: a behavioral study.

Fusional vergence ranges were behaviorally determined for two rhesus monkeys and two human subjects using random dot stereograms as stimuli. The subject performed a two-alternative forced choice form discrimination of discretely presented stimuli and the fusional vergence stimulus was changed during the intertrial intervals. The fusional vergence measurements for the monkey were similar to those for the human subjects.

Animals↗
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↗
PubMed1979

Suprathreshold binocular interactions: the effects of prolonged monocular occlusion.

A simple reaction time paradigm was used to study binocular interactions for suprathreshold grating patterns before and after 8 days of constant monocular occlusion. Prior to patching, subjects demonstrated binocular summation for near threshold contrast stimuli and binocular summation and facilitation for high contrast stimuli. After the period of occlusion, the subjects showed binocular inhibition for high contrast stimuli but still demonstrated binocular summation for low contrast stimuli. The effects of occlusion were reversible and appear to be related to an oculomotor imbalance.

Humans↗
PubMed1978

A sensory mechanism for amblyopia: psychophysical studies.

Psychophysical investigations of the effect of amblyopic process on the sustained and transient channels in the afferent visual pathway are reported. The experiments on photopic luminosity, increment-threshold spectral sensitivity, spatial contrast sensitivity, and reaction-time measures of suprathreshold grating detection provide converging evidence that in naturally occuring amblyopia of humans, the sustained neural channels are more severely affected than the transient channels. However, it appears that the sustained channels are not totally nonfunctional, but rather have a higher intensity requirement than normal.

Amblyopia↗