Search PubMed⌕ Search

Biomedical subjects

R F Hess

Publications and source records attributed to R F Hess.

157 records · Page 9Linked to original sources
PubMed1978

Preliminary results of a physiologically based treatment of amblyopia.

An apparatus has been developed in which high-contrast square-wave gratings are rotated in front of the amblyopic eye while the child is performing some task requiring visual concentration. In the course of three 7-minute treatments 73% of patients treated achieved 6/12 or better; 75% of these patients had previously undertaken conventional or minimal occlusion.

Amblyopia↗
PubMed1978

Central versus peripheral vision: evaluation of the residual function resulting from a uniocular macular scotoma.

This paper examines the contribution of the macular region to visual function. Several test targets were used to measure visual performance within 10 deg of the center of the fovea for normal observers and for an observer with a uniocular central 6-deg scotoma. We conclude that the nature of the test target is more important in the measurement of parafoveal than central vision and that the macular region contributes significantly to the visibility of objects as large as 2.5 deg.

Humans↗
PubMed1977

Assessment of stimulus field size for strabismic amblyopes.

Recently, small-screen measurements have suggested different types of visual loss in strabismic amblyopia. The present experiment examined the influence of field size on this conclusion for low- and high-frequency measurements. The original findings are believed to be independent of the grating field size, because (1) in the present study of 4 amblyopes, normal and amblyopic eyes were affected equally by increasing the number of cycles, and (2) the amblyopes' foveas did not have high-frequency discrimination superior to that of the eccentric area used for fixation.

Amblyopia↗
PubMed1977

Do optical aberrations contribute to visual loss in strabismic amblyopia?

If aberrations contribute significantly to the decreased visual function of strabismic amblyopic eyes, one would predict that (1) the pupil size for optimum resolution should be smaller in the amblyopic than in the normal eyes, (2) increasing target contrast by a constant ratio should not compensate for defocus of an amblyopic eye, and (3) the contrast sensitivity of the amblyopic eye should improve when tested with a stimulus that bypasses the eye's optics. We tested these predictions, using contrast sensitivity techniques, and found no evidence that aberrations contribute to the amblyope's abnormality.

Amblyopia↗
PubMed1977

On the relationship between strabismic amblyopia and eccentric fixation.

Landolt C and grating acuity are compared with that normally expected of the eccentric fixation region for 10 strabismic amblyopes. The findings suggest that 2 populations of amblyopes exist. For some amblyopes visual function is that predicted of the eccentric region used for fixation, whereas for other amblyopes there is a further pathological reduction in visual function. These findings may have an important bearing on the type of orthoptic treatment used for amblyopia.

Adolescent↗
PubMed1977

The effect of corneal edema on visual function.

Corneal edema was produced by atmospheric-induced anoxia and the visual effect was assesed by conventional acuity tests and compared with contrast sensitivity measurements. For the degree of edema which this technique produced, contrast sensitivity was depressed for only high spatial frequencies and could be considered in terms of equivalent defocus. This was not the case ofr a greater degree of edema which was simulated by a diffuser with a particle size that mimics the diffraction effects from an edematous cornea. Equivalent blur was not applicable, since low spatial frequencies were also affected and the letter and contrast sensitivity tests gave radically different results. In the light of these findings, the validity of the present letter acuity evaluation of visual function for patients in which intraocular scattering is involved is questioned.

Cornea↗
PubMedDate not supplied

Contour integration and cortical processing.

Our understanding of visual processing in general, and contour integration in particular, has undergone great change over the last 10 years. There is now an accumulation of psychophysical and neurophysiological evidence that the outputs of cells with conjoint orientation preference and spatial position are integrated in the process of explication of rudimentary contours. Recent neuroanatomical and neurophysiological results suggest that this process takes place at the cortical level V1. The code for contour integration may be a temporal one in that it may only manifest itself in the latter part of the spike train as a result of feedback and lateral interactions. Here we review some of the properties of contour integration from a psychophysical perspective and we speculate on their underlying neurophysiological substrate.

Action Potentials↗
PubMedDate not supplied

Topological disorder in peripheral vision.

One of the most striking properties of the mammalian visual system is that it is only the central part of the visual field, the fovea, where vision is most acute. The superiority of the fovea is particularly evident in tasks requiring accurate spatial localization. It is currently thought that peripheral spatial uncertainty is a simple consequence of the decreased sampling grain of the peripheral field. We show that the topological fidelity of the afferent projection declines with eccentricity away from the fovea and that it is this rather than the sampling grain that underlies the poorer performance of the periphery in tasks involving spatial localization. The combination of normal sampling and a disordered topology results in the periphery having good sensitivity for detection but poor sensitivity for object recognition.

Fovea Centralis↗