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Query: UMLS:C0038379 (strabismus)
 9,317 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

According to Bjerrum [5] and Ammann [2], light attenuation decreases visual acuity at different rates in normals, organic and functional amblyopes. In 27 normal subjects, 19 patients with central fixating squint amblyopia and 12 with organically poor vision, we determined the visually evoked cortical potential (VECP) threshold check size, P100 latency and P2 amplitude for reversing checkerboards of variable size at different levels of luminance. After light attenuation, we found a different rate of change for VECP threshold check size in normal subjects and patients with squint amblyopia, which lessened after the fovea was occluded. With suprathreshold checks, normal subjects and patients with squint amblyopia exhibited significantly smaller amplitude/latency changes after light attenuation than patients with organically poor vision. Only patients with squint amblyopia exhibiting a visual acuity of greater than 0.2 showed smaller VECP changes than normal subjects during light attenuation. According to these findings, the different rate of change in visual acuity after light attenuation in normal subjects and patients with squint amblyopia is locus specific [7] rather than luminance specific [12, 13]. We conclude that cortical disinhibition of the parafoveal retina [20] is responsible for the preservation of visual acuity in squint amblyopia during light attenuation.
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PMID:[VECP (pattern threshold, amplitude, latency) in different light levels. A comparison between healthy eyes, organic and functional amblyopia eyes]. 185 45

Superimposition of a television program onto the black and white checkerboard stimulus used in performing the pattern visual evoked potential (P-VEP) has been found useful in testing adults and children. This study tested normal-vision children under two conditions: with the cartoon superimposition and with the standard black and white checkerboard. P100 amplitudes were decreased slightly with the superimposition, but the variability was not significantly different. Waveforms and latencies were not altered by the addition of the cartoon. The use of cartoon superimposition therefore can be helpful in maintaining attention during P-VEP testing in children, as long as the diminished amplitude characteristic is taken into account.
J Pediatr Ophthalmol Strabismus
PMID:Superimposition of a cartoon program as an aid in recording pattern visual evoked potentials in children. 368 8

Visual evoked response alterations and especially P100 latency were studied in 60 patents with amblyopia caused by strabismus. Patients were divided in two groups according to the mode of fixation of the strabismic eye. Group A included patients with eccentric fixation, and group B, patients with central fixation of the strabismic eye. In all cases visual evoked responses were recorded before and after a 6-month period during which the patients had full-time occlusion of the sound eye. In cases with eccentric fixation of the strabismic eye, P100 latency was more abnormal than in cases with central fixation. In cases where latencies are clearly abnormal before treatment, the prognosis is poor and the results after occlusion of the sound eye are unstable. In contrast, in the cases with normal or nearly normal visual evoked response latencies, the prognosis is better, and these eyes show satisfactory improvement of visual acuity.
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PMID:The prognostic value of visual evoked response latency in the treatment of amblyopia caused by strabismus. 918 49

Microelectrode recordings and optical imaging of intrinsic signals were used to define the critical period for susceptibility to monocular deprivation (MD) in the primary visual cortex of the ferret. Ferrets were monocularly deprived for 2, 7 or >14 d, beginning between postnatal day 19 (P19) and P110. The responses of visual cortical neurons to stimulation of the two eyes were used to gauge the onset, peak, and decline of the critical period. MDs ending before P32 produced little or no loss of response to the deprived eye. MDs of 7 d or more beginning around P42 produced the greatest effects. A rapid decline in cortical susceptibility to MD was observed after the seventh week of life, such that MDs beginning between P50 and P65 were approximately half as effective as those beginning on P42; MDs beginning after P100 did not reduce the response to the deprived eye below that to the nondeprived eye. At all ages, 2 d deprivations were 55-85% as effective as 7 d of MD. Maps of intrinsic optical responses from the deprived eye were weaker and less well tuned for orientation than those from the nondeprived eye, with the weakest maps seen in the hemisphere ipsilateral to the deprived eye. Analysis of the effects of 7 d and longer deprivations revealed a second period of plasticity in cortical responses in which MD induced an effect like that of strabismus. After P70, MD caused a marked loss of binocular responses with little or no overall loss of response to the deprived eye. The critical period measured here is compared to other features of development in ferret and cat.
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PMID:The critical period for ocular dominance plasticity in the Ferret's visual cortex. 1043 53

Visual experience during the critical periods in early postnatal life is necessary for the normal development of the visual system. Disruption of visual input during this period results in amblyopia, which is associated with reduced activation of the striate and extrastriate cortices. It is well known that visual input converges with other sensory signals and exerts a significant influence on cortical processing in multiple association areas. Recent work in healthy adults has also shown that task-relevant visual input can modulate neural excitability at very early stages of information processing in the primary somatosensory cortex. Here we used electroencephalography to investigate visual-tactile interactions in adults with abnormal binocular vision due to amblyopia and strabismus. Results showed three main findings. First, in comparison to a visually normal control group, participants with abnormal vision had a significantly lower amplitude of the P50 somatosensory event related potential (ERP) when visual and tactile stimuli were presented concurrently. Second, the amplitude of the P100 somatosensory ERP was significantly greater in participants with abnormal vision. These results indicate that task relevant visual input does not significantly influence the excitability of the primary somatosensory cortex, instead, the excitability of the secondary somatosensory cortex is increased. Third, participants with abnormal vision had a higher amplitude of the P1 visual ERP when a tactile stimulus was presented concurrently. Importantly, these results were not modulated by viewing condition, which indicates that the impact of amblyopia on crossmodal interactions is not simply related to the reduced visual acuity as it was evident when viewing with the unaffected eye and binocularly. These results indicate that the consequences of abnormal visual experience on neurophysiological processing extend beyond the primary and secondary visual areas to other modality-specific areas.
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PMID:Abnormal visual experience during development alters the early stages of visual-tactile integration. 2689 97