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R Sireteanu

Publications and source records attributed to R Sireteanu.

At least 37 records · Page 2Linked to original sources
PubMed1990

Human amblyopia: structure of the visual field.

Kittens raised with different kinds of abnormal early visual experience (monocular and binocular deprivation, convergent strabismus, eye rotation, asymmetric alternating occlusion, early callosal split) show systematic deficits in the nasal visual field of the affected eye. To test whether abnormal visual experience produces similar deficits in the human visual system, we measured the monocular visual field of humans with subnormal binocular vision (strabismic and anisometropic amblyopes, strabismics with alternating fixation). Eight amblyopes were tested with a computer-assisted static perimetry (Octopus 2000). Twenty other subjects were tested with kinetic perimetry (Goldmann 940), 11 subjects with static perimetry (Goldmann 940). In some of these subjects, we measured the latency of saccades and the accuracy of visually guided pointing toward stimuli presented in the peripheral visual field. Both strabismic and anisometropic amblyopes frequently showed deficits of visual sensitivity in the central part of the visual field, but no systematic deficits in the peripheral field of the amblyopic eyes. Strabismic alternators had practically equal fields in the two eyes. Neither saccadic latency nor pointing accuracy showed a systematic impairment in the nasal visual field. The discrepancy between the field losses in strabismic humans and in cats raised with a surgically induced squint cannot be due to methodological differences, but rather to anatomical differences, or to the different origin of strabismus in the two species.

Adult↗
PubMed1990

A perspective on psychophysical testing in children.

In this paper, we show that the development of acuity in infancy is not due solely to foveal maturation, since there is a clear development of acuity in the peripheral visual field. The development of peripheral acuity, and the naso-temporal asymmetry during early development reinforce the idea that the visual loss in adult strabismic amblyopes is not due to an arrest of development, but rather to the chronic interocular suppression of the deviated eye. The Teller Acuity Card Test does not reliably detect strabismic amblyopia, and therefore should not be recommended as a screening test. However, the test is adequate for diagnosing visual losses in children with organic eye disorders and possibly anisometropia.

Adolescent↗
PubMed1989

[Visual field defects in strabismic amblyopes].

Kittens raised with different kinds of abnormal early visual experience (monocular and binocular deprivation, convergent strabismus, eye rotation, asymmetric alternating occlusion, early callosal split) show systematic deficits in the nasal field of the affected eye. Since the kittens' visual field is tested by monitoring their orienting toward visual stimuli, it is not clear whether these deficits are due to a genuine sensory loss (involving the geniculocortical pathway) or to a sensory-motor impairment (involving the projection through the visual cortex to the superior colliculus). To answer this question, the authors measured the monocular visual field of humans with subnormal binocular vision (strabismic and anisometropic amblyopes, strabismics with alternating fixation). Eight amblyopes were tested with a computerized static perimetry (Octopus 2000). Twenty other subjects were tested with static and kinetic perimetry (Goldmann 940). In some of these subjects, we also tested the latency of saccades and the accuracy of visually guided pointing toward stimuli presented in the nasal or the temporal visual field. Both strabismic and anisometropic amblyopes occasionally showed deficits of visual sensitivity in the central part of the visual field, but no systematic deficits in the peripheral visual field. Strabismic alternators had practically equal fields in the two eyes. Neither saccadic latency nor pointing accuracy showed any asymmetries between the nasal and temporal visual fields. These results seem to contradict a recent report of a nasal hemianopia in deep amblyopia (Mehdorn, 1986); taken together, these results suggest that in adult strabismic humans, a nasal field loss is the exception rather than the rule.(ABSTRACT TRUNCATED AT 250 WORDS)

Amblyopia↗
PubMed1989

[The Teller Acuity Card Test: possibilities and limits of clinical use].

The Teller Acuity Card test was used to examine 49 normal children, 77 with strabismus, 9 with anisometropia and 19 with various organic ocular diseases. The vision of some of these children was also tested with the Landolt C and fixation preference tests. A comparison of the three tests showed that strabismic amblyopia is not reliably detected with the Teller Acuity Cards. On the other hand, this test appears to be a good one for detecting loss of acuity due to ocular diseases.

Amblyopia↗
PubMed1989

Different patterns of retinal correspondence in the central and peripheral visual field of strabismics.

We tested the state of retinal correspondence at different positions in the visual field of ten observers with strabismic and/or anisometropic amblyopia, four strabismic subjects with alternating fixation and three normal controls. Correspondence was evaluated by the subjective displacement of dichoptic stimuli; to estimate the displacement, we used red-green filters, Bagolini striated glasses, polarizing filters and a phase-difference haploscope. Strabismic observers (amblyopes and alternators) frequently showed variations in the angle of anomaly (ie, the amount of shift of space coordinates in the squinting eye) between different regions of the visual field. Correspondence tended to be closer to normal in the central field and more anomalous in the periphery. These findings cannot be explained by the progressive loss of localization sensitivity with increasing eccentricity. We suggest that the different patterns of retinal correspondence in the central and peripheral visual field of some strabismic observers might be due to a mechanism of selective stabilization of binocular connections in the peripheral visual field, where the larger corresponding areas overcome a limited misalignment of the eyes. In the central visual field, normal correspondence is preserved, and diplopia has to be prevented by interocular suppression.

Adolescent↗
PubMed1989

Monocular geometry is selectively distorted in the central visual field of strabismic amblyopes.

Strabismic amblyopia is associated with a distorted perception of visual space. The aim of our study was to investigate the monocular space perception of strabismic observers at several locations in the central and peripheral visual field. We tested nine observers with strabismic and/or anisometropic amblyopia, two strabismic subjects with alternating fixation and two normal control subjects. The task was to align a light stimulus with two vertically arranged reference marks. Testing conditions included three separations of the references along the vertical meridian (10 degrees, 20 degrees and 40 degrees) as well as several presentation sites of the vertical references in the nasal and temporal peripheral visual field (5 degrees, 10 degrees and 20 degrees from fixation). Performance with the amblyopic eye was clearly impaired as compared to the nonamblyopic eye. For alignment along the vertical meridian, all amblyopic eyes showed increased uncertainty in their position judgements. Most of the squinting eyes of amblyopes also displayed a systematic lateral displacement of the test stimulus in relation to the reference marks, in the most extreme case up to almost 7 degrees. Usually, larger errors were found with wider separations of the reference marks. In the peripheral field, the differences between the amblyopic and the nonamblyopic eye diminished or disappeared. Thus, monocular geometry appears to be selectively impaired in the central visual field of the deviated eye of strabismic amblyopes. These spatial distortions might be related to the different states of binocular correspondence in the central vs. peripheral visual field, shown by some strabismic amblyopes.

Amblyopia↗
PubMed1987

Binocular luminance summation in young kittens and adult strabismic cats.

Normal adult cats show a 35% increase in pupil diameter when one eye is illuminated and the other occluded, rather than when both eyes are illuminated. Young kittens show significantly less binocular luminance summation than adult cats (14%). Since these kittens also show a significantly reduced pupillary response to luminance decrements, the postnatal development of binocular luminance summation reflects an increase in pupillary motility, rather than a development of binocular function. Binocular luminance summation is much reduced in esotropic cats (6%), but not in exotropic cats (33%). This finding casts doubts on the usefulness of binocular luminance summation as a measure of binocular function.

Aging↗
PubMed1987

Binocular luminance summation in humans with defective binocular vision.

Subjects with no functional binocularity (no stereopsis and no peripheral fusion) show much less binocular summation of the pupillary response (about 12%) than normal subjects (29%). However, summation is occasionally quite high in clinically stereoblind subjects. The reasons could be the simultaneous use of nonoverlapping fields of the two eyes in large-angle exotropes, peripheral fusion (common in microstrabismus), a mosaic of inputs from the two eyes in different parts of the visual field (often seen in strabismic alternators), or the incomplete suppression of the deviated eye in subjects with double images. These results suggest that the binocular summation of the pupillary response can be used as a test for the simultaneous use of the two eyes, rather than as an index of functional binocularity and stereopsis.

Adult↗
PubMed1986

The relation of monocular optokinetic nystagmus to peripheral binocular interactions.

Human observers with deficient foveal stereopsis often show characteristic abnormalities of monocular optokinetic nystagmus (OKN). The present study examined the effect of binocular interactions in the peripheral visual field on these OKN deficits. A variety of binocular functions (binocular acuity summation, interocular suppression, motion-in-depth) were assessed at various positions throughout the visual field in subjects with deficient or no foveal stereopsis and related to monocular OKN deficits seen with different stimulus field sizes. Extent and location of peripheral binocular interactions accurately predicted the changes in monocular OKN observed with different field sizes. This indicates that the effects of early developmental conditions on cortical and subcortical binocularity, responsible for the deficits of stereopsis and OKN, show very close functional parallels. The results further suggested that monocular OKN deficits and peripheral acuity profiles are determined before the age of 5 yr.

Amblyopia↗
PubMed1985

The development of visual acuity in very young kittens. A study with forced-choice preferential looking.

The development of visual acuity was studied longitudinally in young kittens, using a modification of the forced-choice preferential looking method (FPL) devised by Teller et al. [Vision Res. 14, 1433-1439 (1974)] for human infants. Acuity, defined as the spatial frequency which yields 70% correct responses by a naive observer, shows a 16-fold increase between 2 and 10 weeks of age. At comparable ages, acuity evaluated by this method falls short of the acuity values obtained with the mumping stand or with electrophysiological methods. FPL acuity estimated with a more lenient criterion (58%) comes close to the resolution of the highest-resolving single cells in the striate cortex. These results suggest that the preferential looking procedure provides a method that can be used in kittens over a wide age range, including ages at which it is impossible to use the jumping stand method.

Aging↗
PubMed1985

Forced-choice preferential looking acuity in very young kittens: a model for human development.

The development of visual acuity was studied longitudinally in young kittens, using a modification of the forced-choice preferential looking method (FPL). Acuity, defined as the spatial frequency which yields 70% correct responses by a naive observer, shows a 16-fold increase between 2 and 10 weeks of age. Acuity evaluated this way falls short of the acuity values obtained with the jumping stand or with electrophysiological methods. Acuity estimated with a criterion just above chance comes close to the resolution of the highest-resolving single cells in the striate cortex.

Aging↗
PubMed1984

The development of peripheral visual acuity in human infants. A preliminary study.

In 74 infants, we tested the resolution of gratings centered at 10 degrees in the peripheral visual field. The estimation of acuity was based on the direction of the first saccade from a fixation stimulus toward a peripheral grating stimulus. We also tested the development of the infants' "best acuity", using a method of forced-choice preferential looking (68 infants). Peripheral acuity developed dramatically in the first months of life and reached a plateau at about 4 months. By contrast, "best acuity" continued to increase significantly during the second half of the first year of age. At all ages, peripheral acuity was lower than the resolution evaluated with the same stimuli under free-viewing conditions. We conclude that, in spite of the known immaturity of the fovea in newborns (Abramov et al. 1982), even the youngest infants we tested (2 months old) showed a functional superiority of the central over the peripheral visual field.

Child Development↗
PubMed1982

Binocular vision in strabismic humans with alternating fixation.

Grating acuity, interocular suppression and binocular interaction were evaluated at different positions in the visual field of strabismic humans with alternating fixation. In all cases, the suppression of the deviated eye was most intense in a region corresponding to the fovea of the fixating eye, but reduced or absent in the periphery. In addition, suppression was found in part of the peripheral visual field of the fixating eye. For most subjects, the monocular properties of both eyes were normal. However, for one subject with a strong preference for one of the eyes, visual acuity and luminance detection were selectively impaired in the chronically suppressed regions of the non-preferred eye. Regardless of which eye was currently used for fixation, the visual information available to the subject came from both eyes. In parts of the visual field, the two eyes tended to replace each other. In the far periphery, and especially in the upper and lower hemifield, signals from the two eyes were often combined in a binocular perception of depth.

Amblyopia↗
PubMed1982

The development of the kitten's visual field.

We tested the monocular visual field of 16 kittens aged 13-56 days, by observing their unreinforced visual orienting. At 13-14 days the kittens oriented toward stimuli out of 45 degrees in the nasal field. Until 7-8 weeks, performance was significantly poorer in the nasal field than in the temporal field. This delayed development of the nasal field may be related to the relatively slow development of the uncrossed retino-geniculate projection and of the pathway through the visual cortex to the superior colliculus.

Aging↗
PubMed1982

Human amblyopia: consequence of chronic interocular suppression.

In human strabismic amblyopes, visual acuity is selectively impaired in the central part of the visual field of the deviated eye. The acuity loss is usually asymmetric and depends on the direction and magnitude of the interocular misalignment. By contrast, in anisometropic amblyopes, the loss of acuity extends symmetrically in both the nasal and the temporal fields of the defocussed eye. Binocular interaction, including stereopsis, is selectively lost in the central part of the visual field of both strabismic and anisometropic amblyopes, but preserved in the periphery. For both groups of subjects, the areas of acuity and binocularity loss correlate well with the regions of interocular suppression. These findings support the idea that amblyopia arises at a central locus in the visual system, as a consequence of chronic interocular suppression.

Amblyopia↗