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R Sireteanu

Publications and source records attributed to R Sireteanu.

44 records · Page 3Linked to original sources
PubMed1980

The "vertical effect" in human squint amblyopia.

Grating acuity was tested in seven squint amblyopes as a function of orientation. In the squinting eyes of six unilateral amblyopes, the resolution for vertical gratings was much lower (by about 1/2 octave) than that of horizontal gratings. The non-amblyopic eyes of these subjects showed a normal "oblique effect". In one bilateral amblyope the selective loss of resolution for vertical contours was found in both eyes. This effect is well correlated with the reduced incidence of cortical cells encoding vertical contours in squinting cats. Both findings can be interpreted as an adaptive modification of the central visual system to alleviate the selective doubling of the vertical contours caused by strabismus.

Amblyopia↗
PubMed1978

Psychophysical and neurophysiological investigations of the effects of early visual deprivation in the cat.

Cats can locate objects with their monocularly deprived eye best in the monocular segment of their visual field. In contrast they show a marked deficit towards the midline and an almost total failure in the binocular segment contralateral to the deprived eye. This correlates well with the relative frequency of units in the superior colliculus activated by that eye. The performance of the cat in a pattern discrimination task is three times better with the normal eye than with the deprived eye if the patterns have to be detected on a background of visual noise. This correlates well with the loss of units in the visual cortex activated by the deprived eye. There is no loss of visual acuity in the units in lamina A of the lateral geniculate body, but in lamina A1 visual acuity is reduced to half the normal value due to monocular deprivation.

Action Potentials↗
PubMedDate not supplied

Distortions in two-dimensional visual space perception in strabismic observers.

Amblyopic subjects were asked to memorize circles of different radii (2, 4 and 6 degrees), and then to reconstruct them monocularly with each eye, point by point (12 points per circle). The resulting two-dimensional maps of visual space showed considerable distortions, including expansion, shrinkage and torsion of specific regions of the visual field of the amblyopic eye, but not the normal eye. Based on the differences between the two eyes, we computed complex two-dimensional patterns (gratings, checkerboards, optotypes, written text, natural scenes) as "seen" monocularly with the amblyopic eye. These reconstructed patterns were then compared with drawings of the same patterns observed through the amblyopic eyes of the same subjects. The reconstructed patterns only partially reflected the actual perception for the amblyopic eyes. The compensation of complex, globally-extended scenes in comparison to the distortions obtained by local, punctate settings probably reflects cooperative interactions occurring at higher brain levels.

Adult↗
PubMedDate not supplied

Eye alignment and cortical binocularity in strabismic kittens: a comparison between tenotomy and recession.

Interocular alignment was assessed by corneal light reflex photography in 15 normal and 26 strabismic kittens. Strabismus was induced at 3-4 weeks of age by severing one extraocular muscle (tenotomy), by cutting and reinserting the muscle at another position on the ocular globe (recession), or by combining recession of the medial rectus muscle with resection of the lateral rectus muscle of the same eye. Nineteen strabismic and five normal kittens were followed longitudinally from 12 days to about 6 months of age. Three out of six longitudinally followed tenotomized cats and six out of the 13 recessed cats conserved their postoperative ocular deviation throughout the testing period ("large-angle strabismics"). Three tenotomized and seven recessed cats showed a transient deviation for 1-2 weeks after surgery, after which the interocular deviation diminished to values found in normal cats ("microstrabismic" cats). Both recessed-resected cats showed a transient interocular deviation. In spite of their different developmental histories, all cats showed a clear breakdown of binocularity in area 17. Large-angle strabismics showed a dominance of the non-operated eye, while in microstrabismic cats, both eyes were equally effective in driving cortical cells. It thus appears that a transient strabismus is sufficient to produce a reduction of binocularity in area 17.

Animals↗