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  • 1
    Electronic Resource
    Electronic Resource
    Amblyopia occurs in retinal ganglion cells in cats reared with convergent squint without alternating fixation (1979)
    Springer
    Experimental brain research 35 (1979), S. 559-582 
    Details
    ISSN: 1432-1106
    Keywords: Strabismus ; Amblyopia ; Retinal ganglion cells ; Visual acuity ; Contrast sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The spatial resolving power, contrast sensitivity, and receptive field properties of retinal ganglion cells were studied in cats reared with either convergent or divergent squint in one eye. Sustained-X cells in the area centralis of the squinting eye of the cats with esotropia without alternating fixation showed significantly poorer spatial resolution, and reduced contrast sensitivity compared with cells in the area centralis of the normal eye. These amblyopic sustained-X cells in the area centralis of the squinting eye had receptive field characteristics similar to those found in immature cells of young kittens. They had a shallow sensitivity gradient within a relatively widespread centre zone and a weak and widespread inhibitory surround. In contrast, the sustained cells in the area centralis of the normal eye revealed a typical, well defined, small centre zone with its sensitivity gradient extremely steep and its inhibitory surround strong and confined. A minor degree of amblyopia was also found in transient Y-cells in the area centralis of the squinting eye of these cats. However, no loss of resolving power was found in the cells in the area centralis of the squinting eye of the cats with esotropia or exotropia which showed alternating fixation. Thus, amblyopia occurs in those eyes which have lost the use of the area centralis as the normal visual axis during early postnatal development, and its organic lesion is already apparent in the retinal ganglion cells — the third order neurone in the afferent visual system. It is suggested that the loss of the ability to fixate results in inadequate stimulation of the central retinal ganglion cells due to the habitual presence of blurred images at the area centralis which prevents their full development during the critical period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236772
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Properties of LGN cells in kittens reared with convergent squint: A neurophysiological demonstration of amblyopia (1976)
    Springer
    Experimental brain research 25 (1976), S. 63-77 
    Details
    ISSN: 1432-1106
    Keywords: Kitten LGN ; Single cell ; Convergent squint ; Visual acuity ; Amblyopia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The spatial resolution of LGN cells has been studied in 4–5 month old kittens raised with convergent squint surgically produced in one eye at the age of 3–4 weeks. The ‘sustained’ cells which received inputs from the central retina of the squint eye showed significantly poorer spatial resolution (determined by the highest spatial frequency of a sinusoidal grating to which a cell responded with modulated firing) than those which received inputs from the central retina of the normal eye. The spatial resolution of cells which received inputs from the peripheral retina of the squint eye was not different from that of cells receiving inputs from the peripheral retina of the normal eye. The visual latency of ‘sustained’ cells which received an input from the area centralis of the squint eye was considerably lengthened and the response showed a sluggish onset. Thus the most important clinical symptom of amblyopia, namely the reduction of foveal visual acuity, has been demonstrated in kittens raised with unilateral vonvergent squint. The results suggest that the lesion responsible for amblyopia due to squint might be a functional degeneration of the high spatial frequency tuning cells in the pathway prior to the visual cortex, i.e. in the retina or LGN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237326
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Behavioural studies of spatial vision in cats reared with convergent squint: Is amblyopia due to arrest of development? (1979)
    Springer
    Experimental brain research 34 (1979), S. 11-26 
    Details
    ISSN: 1432-1106
    Keywords: Convergent squint ; Amblyopia ; Spatial vision in cat ; Contrast sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Visual acuity and contrast sensitivity were measured behaviourally in normal adult cats and cats reared with monocular convergent squint from 3, 6, 8, 12, and 24 weeks of age. The visual acuity of the squinting eye was significantly lower than that of the non-squinting eye in cats with squint from 3, 6, and 8 weeks of age. No significant difference in acuity between eyes was found in the 12- and 24-week squinting cats and in the controls. Contrast thresholds at all spatial frequencies tested (range 0.13–2.0 c/ °) were higher in the squinting eye than in the non-squinting eye of cats with squint from 3 and 6 weeks of age, but differences were greater at the higher spatial frequencies. In the 8-week squinting cat, contrast thresholds were increased only at higher spatial frequencies. No significant differences in contrast sensitivity were found in the cat with squint from 24 weeks of age and in the controls. The degree of disturbance of spatial vision in squinting cats was most related to the age at onset of the squint, i.e., the earlier the onset, the more profound the amblyopia. The period of susceptibility extended from about 3 to 12 weeks of age. When compared with data on the development of visual acuity in kittens, the pattern of results from the present study suggests that convergent squint can arrest the development of spatial vision.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238338
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Relationship between amblyopia, LGN cell ‘shrinkage’ and cortical ocular dominance in cats (1982)
    Springer
    Experimental brain research 45 (1982), S. 243-252 
    Details
    ISSN: 1432-1106
    Keywords: Amblyopia ; Strabismus ; Penalisation ; Ocular dominance ; Perikaryal size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Six cats were reared with surgically produced squint or atropinisation of one eye during the sensitive period of development. Five cats were reared without any ocular interference but in the same environment as the experimental cats. Four of these normally reared cats provided control data for perikaryal size. When the cats were 5–8 months old, the ocular dominance distribution of cells in area 17 of the visual cortex was determined, and measurements of visual acuity of cells in the LGN receiving inputs from the area centralis were carried out. Following the neurophysiological experiments, the perikaryal sizes of LGN cells receiving fibres from the area centralis of the left and right eye were measured from Nissl stained sections of the brain of each cat. Cats which showed greater amblyopia (loss of acuity) of LGN cells driven from the area centralis of the experimental eye, showed a greater degree of apparent ‘shrinkage’ of Nissl stained LGN cells and a greater proportion of cortical cells excited by the control eye than by the experimental eye. All experimental cats showed a loss of binocularly driven cells, regardless of whether their LGN cells were amblyopic or not, and whether they had ‘shrunk’ or not. However, when LGN cell amblyopia was present, the degree of amblyopia and ‘shrinkage’ of the LGN cells were correlated with the degree of loss of binocular cells also.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235784
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Loss of spatial resolution of lateral geniculate nucleus neurones in kittens raised with convergent squint produced at different stages in development (1978)
    Springer
    Experimental brain research 31 (1978), S. 207-220 
    Details
    ISSN: 1432-1106
    Keywords: Kitten LGN ; Convergent squint ; Visual development ; Amblyopia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In twelve kittens, convergent squint was surgically produced at either 3, 6, 8, 10, 13, or 16 weeks. When these kittens reached the age of 4–8 months, the spatial resolution of ‘sustained’ cells which received inputs from the area centralis in layers A and A1 of both the left and right lateral geniculate nucleus (LGN) was measured under nitrous oxide/halothane anaesthesia, using the highest spatial frequency of a sinusoidal grating resolved by cells as a measure of cellular visual acuity. Spatial resolution of cells fed by the squinting eye's area centralis was poorest in the kittens in which the squint was produced at 3 weeks. The resolution of the cells driven by the area centralis of the squinting eye gradually improved for the kittens in which the squint was produced at progressively later stages. There was no effect of convergent squint on the resolving power of cells in the kittens in which squint was produced at 13 weeks and 16 weeks. The developmental curve of spatial resolution of LGN cells obtained from normal kittens of different ages was found to fit very closely with a plot of the spatial resolution of cells driven by the squinting eye against age at squint production. These results suggest that the loss of spatial resolution (amblyopia) in the eye with convergent squint is due to the arrest of development of spatial resolution during the sensitive period in early postnatal life. Clinical implications are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237600
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    Paper (German National Licenses)
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