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Biomedical subjects

U Yinon

Publications and source records attributed to U Yinon.

At least 55 records · Page 3Linked to original sources
PubMed1984

Eyelid closure effects on the refractive error of the eye in dark- and in light-reared kittens.

Kittens reared in the dark with their eyelids sutured postnatally on one side have developed hypermetropia in the closed eye (average: +2.75 D for the horizontal meridian). This was significantly different (0.01 greater than p greater than 0.005) from the results of the open eye (+1.67 D; 180 degrees). The closed eye of light-reared kittens had similar refractive error (+0.33 D) to that of their open eye (+0.50 D), and to that of kittens light-reared with both eyes open (+0.75 D). Axial length of the closed eye in the dark-reared kittens and its corneal refractive power were smaller in comparison to the results for the open eye. It was concluded that in kittens lid closure during development in the dark induces hypermetropia.

Animals↗
PubMed1984

The optical effects of eyelid closure on the eyes of kittens reared in light and dark.

Monocular closure surgically performed during development by suturing the eyelids induced less hyperopia in the closed eye of light reared kittens (+0.95 Diopters) in comparison to the closed eyes of lid sutured dark reared kittens (+2.61 D). The normal control cats were also slightly hypermetropic (+0.69 D). While a certain proportion of myopic eyes was found in the monocularly closed light reared kittens and in the normal control cats, no one eye was myopic either in the operated or nonoperated dark reared kittens. Lid suture was found to considerably increase the hyperopia also in adult cats. The incidence of astigmatism was 47.0% for the closed eye in the lid sutured light reared kittens and 64.7% for their open eyes; for the lid sutured dark reared kittens the proportions were 45.4% and 54.5%, respectively. The incidence of astigmatism was 20.2% for the eyes of the normal control cats. Axial length of the closed eye of light (19.00 mm) and of dark (19.45 mm) reared kittens was smaller in comparison to that of the normal control cats (20.38 mm). The corneal curvature of the closed eyes of light (8.09 mm) and of the dark (8.64 mm) reared kittens was flatter than in the normal controls (7.11 mm). It is concluded that lid closure in kittens has a corneal effect, accentuating the tendency for hypermetropia naturally occurring in the dark. In the light lid closure results in an imbalanced combination of the corneal and the (axial?) visual deprivation effects, causing a considerable variability in the refractive error with a tendency for cancellation of the naturally occurring hyperopia.

Animals↗
PubMed1984

Myopia induction in animals following alteration of the visual input during development: a review.

In this review the effects of changes in the quality of the visual environment on the development of myopia during eye growth in various mammalian and avian species are described. The effect of changes in the light/dark cycle on myopia development has been studied only in the avian eye, mainly that of the domestic fowl. In the eyes of chicks reared from hatching to maturity under continuous illumination, the following findings were reported: myopia, astigmatism, increases in axial length and equatorial width, shallow anterior chamber, increase in corneal diameter, reduction of corneal curvature, increased intra-ocular pressure (IOP), low outflow facility, reduction in aqueous space, buphthalmos, macrophthalmos and glaucoma. The above mentioned changes were consistent in the majority of the studies. In a few experiments where a change in one of the above mentioned parameters was not found, no tendency for the opposite condition was reported. When the illumination level of the visual environment was changed in the avian eye there was an increase in the total size of the eye as well as exophthalmos. Other parameters were not examined. It is quite possible that myopia and eye enlargement in avians are caused by entirely different processes than myopia and eye enlargement in mammals since they can be induced either by changes in the diurnal rhythm or by low intensity light. The involvement of the pineal gland in the control of eye growth in avians is therefore possible. The effect of continuous dark rearing was studied in the avian and in the mammalian eye. In developing chicks reared in continuous darkness some enlargement of the eye took place, but a condition of hyperopia was found as opposed to the expected myopia. This result is in agreement with the results of experiments performed on monkeys and cats reared from infancy to adulthood in complete darkness. The effect of near vision conditions during growth was studied in monkeys, cats and chicks confined to small chambers, cages or rooms. A slight myopia was usually obtained in all of the above species but the incidence of myopia increased consistently in the experimental animals compared to the normal controls. The effect of optically restricting the visual field during growth was studied in chicks. Using special occluders, the eyes of the chicks were exposed only to the frontal fields of vision. This manipulation induced a considerably high myopia and an increase in the axial length of the eye and in the depth of the anterior chamber. Removal of the occluders resulted in a reversal of the induced myopia.(ABSTRACT TRUNCATED AT 400 WORDS)

Accommodation, Ocular↗
PubMed1982

The hemispheric dominance of cortical cells in the absence of direct visual pathways.

Unit recording was carried out in the visual cortex of split chiasm and optic tract-sectioned adult cats. From the proportions of the visually responsive and unresponsive cells found in each hemisphere of the operated cats it was concluded that the indirect pathway via the corpus callosum becomes visually inactive under these conditions. However, the direct geniculocortical pathway remains visually active. Thus, it was assumed that unilateral or bilateral elimination of the decussating pathway has a crucial effect on the amount of interhemispheric callosal transfer of basic visual functions.

Animals↗
PubMed1982

Central gating of developmental plasticity in kitten visual cortex.

1. In nine 4-week-old, dark-reared kittens we sutured one eye closed and rotated the other surgically. The kittens then grew up in a normally lighted animal colony with adequate room to play.2. For about two weeks after surgery their visual-motor co-ordination did not differ from that of kittens with conventional monocular deprivation; then severe disturbance of visually guided behaviour became progressively more apparent until, after another two to three weeks, all the kittens stopped responding to most visual stimuli entirely. At that point their behaviour in an unfamiliar environment closely resembled that of binocularly deprived cats exposed to light for the first time.3. Four weeks (n = 3) and 6 months (n = 6) after surgery, we examined the visual cortex with single-unit recordings, and with evoked potentials elicited by electrical stimuli and patterned lights. We obtained the single-unit recordings from 586 neurones of the striate cortex in both hemispheres, both ipsi- and contralateral to the deprived eye.4. The single-unit recordings and the evoked potentials showed a clear relation between the kitten's abnormal visual behaviour and the functioning of the striate cortex. Only about half the normal percentage of cells responded to light, and most of those which did react had abnormal receptive field properties: they responded only sluggishly even when the light stimuli were aligned optimally.5. We also evoked cortical potentials with phase alternating square wave gratings of variable contrast and spatial frequency. The amplitude of the potentials indicated that contrast-sensitivity was reduced at all spatial frequencies.6. In the kittens tested 4 weeks after surgery, ocular dominance had shifted toward the open rotated eye but this shift was considerably less pronounced than in control kittens monocularly deprived for a comparable period of time.7. In the kittens tested 6 months after surgery fewer cells than normal were binocular; ocular dominance had not shifted towards the open eye.8. Numerous control experiments indicated that these abnormalities did not result from transitory immobilization of the eye alone nor from lesions of the retina or of the optic nerve.We infer that a central mechanism prevents the inappropriate signals from the rotated eye from influencing the consolidation of central pathways.

Animals↗
PubMed1982

Evidence for long-term functional plasticity in the visual cortex of adult cats.

1. Vision was investigated with behavioural and electrophysiological techniques in three groups of cats: (a) two normally raised kittens in which one eye was rotated at an age of 3 months, (b) three adult cats in which one eye had been rotated and the other closed 6 months prior to recording, (c) two adult cats in which first one eye had been rotated and the other closed and subsequently, after one year, the rotated eye had been closed and the normal eye re-opened. The latter two cats were investigated 6 and 12 months after reverse suture, respectively. All adult cats were at least 2 years old when operated on for the first time.2. Behavioural analysis revealed that the kittens of the first group no longer used the rotated eye for fixation, visuo-motor behaviour being impaired when tested through this eye. Binocularity was found to be disrupted to nearly the same extent as in kittens made strabismic at the beginning of the critical period. In addition, ocular dominance was shifted towards the normal eye.3. The adult cats in the second group developed a virtually complete neglect of the visual modality subsequent to a period of severely disturbed visuo-motor behaviour.4. These behavioural abnormalities were associated with clear alterations in the functional state of striate cortex. Only 47% of the recorded cells could be driven with light, the majority of these reactive neurones yielding only sluggish responses to optimally aligned stimuli. The ocular dominance distribution showed a significant reduction of binocular cells but gave no indication of a shift in ocular dominance towards either of the two eyes. Moreover, contrast sensitivity as assessed with pattern-evoked potentials was significantly reduced.5. The remaining two animals that were reverse sutured after the visual neglect had developed showed complete behavioural recovery when tested through the re-opened normal eye. However, this recovery was not instantaneous and occurred only after the cats had been forced to use their visual sense.6. Behavioural recovery was paralleled by an increase of cortical reactivity to normal levels and by a marked increase in binocularity. This gain increase of excitatory transmission was, however, selective for neurones dominated by the normal eye, leading to a bias in ocular dominance towards this eye.7. The observed modifications in the functional state of striate cortex indicate that reversible changes in the gain of excitatory transmission can still occur beyond the end of the classical critical period. These long-lasting changes in synaptic efficiency appear to follow the rules postulated by Hebb for adaptive synaptic connexions.

Animals↗
PubMed1982

Orientation disparity and plasticity of cortical cells in kittens following surgical rotation of the eye.

We have studied the effect of surgically induced monocular rotation of the eye on cells in visual area 17 of normal kittens (N = 420 cells) and of kittens monocularly deprived (N = 296 cells) at early (1-1.5 months) or late (3 months) ages. The receptive fields of cortical neurons in monocularly deprived kittens of the early operated group were abnormal in shape, a condition which is reflected by the high proportions of cells missing orientation (46.9%) and direction (47.7%) specificity when driven through the rotated eye. In addition, many cells (46%) were visually inactive in these kittens. The proportions of the above cell groups were less pronounced in the operated kittens with binocular vision and in all late operated kittens, indicating a specific effect of the rotation itself. In the early operated kittens with binocular vision, the rotation resulted in 35.9% binocular cells in the hemisphere contralateral and 40.0% in the hemisphere ipsilateral to the rotated eye. The results for the monocularly deprived early operated kittens were 42.8% and 21.5% respectively. Thus, the rotation was effective in limiting the influence of the deprivation to only the contralateral hemisphere. The distribution of the cells in accordance with their receptive field orientations following correction for the surgical rotation shows a considerable disturbance to orientation specificity, as reflected by the wide range of angular disparities found for the binocular cells. While for three kittens (28 cells) a tendency toward the zero line was found, for four kittens (28 cells) we could not prove, it indicating that a compensation for the interocular difference surgically induced is not seen.

Adaptation, Physiological↗
PubMed1982

The effects of early visual experience followed by prolonged dark rearing on visual cortex cells of cats.

Five groups of kittens (N = 13) were dark reared for 9.5-20 months following normal binocular exposure of 0-85 days after natural eye opening and 1 month of monocular deprivation. For comparison, kittens monocularly deprived (MD) for 10 months (N = 2) and normal adult cats (N = 13) served as controls. The ocular dominance distribution of cortical cells showed a clear (although small) bias in the first group of kittens which received the minimal exposure. A striking effect was obtained in the proportion of visually unresponsive cells (55.1%) in this first group of cats. Concerning orientation and direction selectivity, the highest proportions of nonselective cells, 16.1% and 33.3%, were obtained in the first two groups of cats respectively. It was concluded that periods of monocular deprivation shorter than that used in the present study (4 weeks) and without any previous visual experience would be ineffective if followed by a year or more of total absence of visual experience. Prolonged dark rearing therefore, masks the effect of prior monocular deprivation to a large extent. In addition, the results emphasize the fact that the age factor is more important than the duration of the monocular visual experience.

Aging↗
PubMed1980

Monocular deafferentation effects on responsiveness of cortical cells in adult cats.

Following chronic (2-3 months) unilateral eye enucleation in cats, an increase was found in the proportion of diffuse (5.4%), orientation bias (8.3%) and non-oriented (9.6%) receptive fields of cortical cells above the normal level. A reduction in small size receptive fields (< 0.8 sq. degrees) and in cells with the smallest (< 22.5 degrees) range of orientation was found in chronic cats in comparison to normal cats. Acute cats (enucleation 1 day before recording were either intermediately between chronic and normal cats, or were similar to the latter. The small differences found in receptive field organization, the relative absence of inactive cells and the normal organization of the orientation columns do not indicate a substantial change in the visual properties resulting from deafferentation.

Afferent Pathways↗
PubMed1978

Chronic asymmetry in the extraocular muscles of adult cats: stability in binocularity of cortical neurons.

During the first 2 weeks following unilateral severance of the 6 extraocular eye muscles in adult cats, the operated eye is partially immobile as shown by electrooculographic (EOG) recordings of horizontal eye movements. Although the motility of the operated eye improves with time (mainly in terms of amplitude but also with regard to direction and frequency of movements), it does not reach (up to 2 months) the level of the normal eye. Unit recording was done in visual cortex area 17 of these cats while paralyzed, either immediately (acute group, 5 cats), or 3-60 days (chronic group, 6 cats) following the operation. The number of visually inactive cells was slightly higher in the operated cats (13.8%) than in normal cats (8.3%), but the number of nonoriented cells or cells with disorganized receptive fields was similar in both groups of cats. The proportion of binocularly activated cells in the operated cats, especially in the chronic group (greater than 10 days after the operation, 71.2% of 153 cells), was similar to that of the normal control cats (72.8% of 236 cells). No ocular dominance shift was found when either the operated eye was compared to the normal one or the ipsilateral eye to the contralateral one. It was concluded that distortion of afferent proprioceptive input from the extraocular eye muscles to visual centers has no effect on binocularity of cortical neurons in adult cats.

Animals↗
PubMed1978

On the question of neuronal plasticity in the mature visual cortex.

In adult cats one eye was surgically immobilized by sectioning the eye muscles, or inverted by 180 degrees rotation, or pattern-deprived by suturing the eyelids for 1-12 weeks. Orientation and direction selectivity of cortical cells and binocularity were preserved; no shift in the ocular dominance distribution toward either eye was found. The visual cortex of adult cats is therefore not susceptible to changes in the content of the visual input.

Age Factors↗
PubMed1977

Inverted vision surgically induced in experienced cats: physiology of the primary cortex.

The physiological effects of inversion of vision were studied in the visual cortex of five adult cats following 180 degrees surgical rotation of one eye for 2-3 months. The other eye was closed in order to prevent binocular conflicting visual input in the period between eye inversion and unit recording. The distribution of neurons according to their ocular dominance was very slightly different from that of normal cats. The retinotopic map was stable in that respect that receptive fields were spatially located in their expected position in accordance with the inversion induced; they reversed positions when maps of the two eyes were compared. Directional selectivity was also preserved; the preferred directions of binocularly activated units were found to be in opposition when responses from the normal and the inverted eyes were compared.

Adaptation, Physiological↗
PubMed1977

Effect of visual environment on refractive error of cats.

33 eyes of 18 cats raised in cages or in small rooms under conditions of near vision were compared with 22 eyes of 11 street cats. Refraction of the caged cats showed that three quarters of them were myopic (average:-0.8 D) while 87.5 percent of the street cats were hypermetropic (average: +1.4 D). The antero-posterior diameter was practically equal in both groups (20.4 mm) and in both myopic and hypermetropic eyes. The site of the permanent refractive changes is suggested to be the lens.

Animals↗