Early visual experience shapes the representation of auditory space in the forebrain gaze fields of the barn owl.
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Auditory spatial information is processed in parallel forebrain and midbrain pathways. Sensory experience early in life has been shown to exert a powerful influence on the representation of auditory space in the midbrain space-processing pathway. The goal of this study was to determine whether early experience also shapes the representation of auditory space in the forebrain. Owls were raised wearing prismatic spectacles that shifted the visual field in the horizontal plane. This manipulation altered the relationship between interaural time differences (ITDs), the principal cue used for azimuthal localization, and locations of auditory stimuli in the visual field. Extracellular recordings were used to characterize ITD tuning in the auditory archistriatum (AAr), a subdivision of the forebrain gaze fields, in normal and prism-reared owls. Prism rearing altered the representation of ITD in the AAr. In prism-reared owls, unit tuning for ITD was shifted in the adaptive direction, according to the direction of the optical displacement imposed by the spectacles. Changes in ITD tuning involved the acquisition of unit responses to adaptive ITD values and, to a lesser extent, the elimination of responses to nonadaptive (previously normal) ITD values. Shifts in ITD tuning in the AAr were similar to shifts in ITD tuning observed in the optic tectum of the same owls. This experience-based adjustment of binaural tuning in the AAr helps to maintain mutual registry between the forebrain and midbrain representations of auditory space and may help to ensure consistent behavioral responses to auditory stimuli. (+info)
The effects of spectacle wear in infancy on eye growth and refractive error in the marmoset (Callithrix jacchus).
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We made a comprehensive study, involving observations on 45 marmosets, of the effects on ocular growth and refraction of wearing spectacles from the ages of 4-8 weeks. This period was within the period early in life when the eye grows rapidly and refraction changes from hyperopia to its adult value of modest myopia. In one series of experiments we studied the effect of lenses of powers -8, -4, +4 and +8D fitted monocularly. In another series of experiments we studied the effect of lenses of equal and opposite powers fitted binocularly, with the two eyes alternately occluded, so as to give an incentive to use both eyes, and in particular to accommodate, for at least part of each day, through the negative lens. The vitreous chamber of eyes that wore negative lenses of -4D or -8D, combined with alternate occlusion, elongated more rapidly than that of the fellow eye (negative lens eye-positive lens eye, 0.21 +/- 0.03 mm (S.E.M.), P < 0.01 and 0.25 +/- 0.06 mm, P < 0.05, respectively) and became relatively more myopic (2.8 +/- 0.26D, P < 0.01 and 2.4 +/- 0.61D, P < 0.05 respectively). Eyes that wore -4D lenses monocularly elongated more rapidly and became myopic than fellow eyes. Eyes that wore +4D or +8D lenses were less strongly affected: animals that wore +8D lenses monocularly (without alternate occlusion) developed a slight relative hyperopia (0.99 +/- 0.21D, P < 0.01), with the more hyperopic eyes also slightly shorter (0.09 +/- 0.05 mm) than their fellow eyes, but eyes wearing +4D lenses were not significantly different from their fellow eyes. Animals that wore -8D lenses monocularly (without alternate occlusion) developed a slight relative hyperopia after three weeks of lens-wear (0.85 +/- 0.26D, P < 0.05). These were the only eyes that responded in a non-compensatory direction to the optical challenge of spectacle wear, and we interpret this effect as one due to visual deprivation. After the removal of lenses, the degree of anisometropia slowly diminished in those groups of animals in which it had been induced, but in the three groups in which the largest effects had been produced by lens-wear the overall mean anisometropia (0.68 +/- 0.24D, P < 0.01) and vitreous chamber depth (VCD) discrepancy (0.09 +/- 0.03 mm, P < 0.01) were still significant at the end of the experiments, when the animals were 273 days old. The reduction of anisometropia in these groups was associated with an increase in the rate of elongation of the vitreous chamber in the eyes that had previously grown normally i.e. the less myopic eyes grew more rapidly than their fellow eyes: in the seven weeks following lens-wear these eyes became more myopic and longer than normal eyes (refraction P < 0.001; VCD P < 0.001). Control experiments showed that occlusion of one eye for 50% of the day had no effect on eye growth and refraction, and therefore that alternate occlusion itself had no effect. (+info)
Rehabilitation of children with cataracts.
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Over a period of 10 years, 160 children with cataracts underwent operation at the University of Tennessee Medical Center, Memphis. The surgical, optical, and psychosocial rehabilitation of these patients was analyzed and studied. The optical rehabilitation included patients with glasses, intraocular lens implants, epikeratophakia, and contact lenses. Seventy three of these patients were chosen at random and reevaluated as to visual outcome, and 46 were subjected to a psychosocial test to evaluate their quality of life and their rehabilitation. Eighteen of these were also given a psychosocial test to evaluate the quality of life enjoyed by these children at an older age following treatment for the cataract. Surgical, optical, and psychosocial rehabilitation of such children is also discussed. This is the first report of the psychological evaluation of such children. The further needs of these children as they approach adulthood are discussed in detail. (+info)
Functional visual loss in amblyopia and the effect of occlusion therapy.
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PURPOSE: The aim of this study was to define the nature of functional visual loss in amblyopia and to identify those subjects whose amblyopia is chiefly due to one or more of the following deficits: abnormal contour interaction, abnormal eye movements, abnormal contrast perception, or positional uncertainty. METHODS: Fifty amblyopic children with a mean age of 5.6+/-1.3 years were referred from diverse sources. In addition to routine orthoptic and optometric evaluation the principal visual deficits in the amblyopic eye of each subject were identified using the following measures of visual acuity: high contrast linear, single optotype, repeat letter and low contrast linear, plus Vernier and displacement thresholds. These measures were repeated as the children underwent a prescribed occlusion therapy regime, after parental consent. RESULTS: All amblyopic subjects demonstrated a functional loss in each of the tests used, and occlusion therapy appeared to improve all aspects of the amblyopia. High contrast visual acuity was not always the primary deficit in visual function, and when amblyopic subjects were divided according to their primary visual loss, this visual function was found to show the greatest improvement with treatment. CONCLUSIONS: These results suggest that to successfully identify the primary visual deficit and monitor the success of occlusion therapy it is necessary to assess other aspects of visual function in amblyopia. (+info)
Refractive associations with cataract: the Blue Mountains Eye Study.
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PURPOSE: To assess the relationship between myopia and age-related cataract in a defined older population. METHODS: A cross-sectional study of 3654 people aged 49 to 97 years was conducted in the Blue Mountains near Sydney, Australia, from 1992 through 1994. General medical, eye, and refractive history and information about confounders were collected by questionnaire. Participants had a detailed determination of refraction, and the spherical equivalent refraction of each eye was calculated. The Wisconsin Cataract Grading System was used in masked grading of slit lamp and retroillumination lens photographs, to assess presence and severity of nuclear, cortical, and posterior subcapsular (PSC) cataract. Data from both eyes were analyzed by the generalized estimating equation method, adjusting for cataract risk factors. RESULTS: Included in the analysis were 7308 eyes. A history of wearing distance glasses, excluding eyes with current hyperopic refraction, was used as a proxy for myopia. Subjects who had worn distance glasses were more likely to have nuclear cataract (odds ratio [OR] 1.3; confidence interval [CI] 1.0-2.1). After stratification by age at first wearing distance glasses, this relationship remained only for people who first wore distance glasses after age 40 years (OR 1.3; CI 1.0-1.8), which suggested a myopic refractive shift from developing nuclear opacity and was supported by the weak association found between current myopic refraction and nuclear cataract (OR 1.3; CI 1.0-1.6). Eyes with onset of myopia before age 20 years had the greatest PSC cataract risk (OR 3.9; CI 2.0-7.9). This was supported by the finding of an association between current myopic refraction and PSC cataract (OR 2.5; CI 1.6-4.1). PSC cataract was inversely associated with hyperopia (OR 0.6; CI 0.4-0.9). Refraction-related increasing odds were found between PSC cataract and myopia: low myopia (OR 2.1; CI 1.4-3.5), moderate myopia (OR 3.1; CI 1.6-5.7), and high myopia (OR 5.5; CI 2.8-10.9). High myopia was associated with PSC, cortical, and late nuclear cataract. CONCLUSIONS: Early-onset myopia (before age 20 years) may be a strong and independent risk factor for PSC cataract. The findings suggest the possibility of a dose response between levels of myopia and PSC cataract. Nuclear cataract was associated with presumed acquired myopia, whereas high myopia was associated with all three types of cataract. (+info)
Treatment of photosensitive epilepsy using coloured glasses.
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A recently introduced optometric technique, colorimetry, enables the perceptual effects of ophthalmic tints to be evaluated subjectively, optimized, and then prescribed in tinted spectacles. The new technique is beneficial in reducing visual stress in patients with dyslexia and migraine. We describe an open trial designed to ascertain: (1) whether the colorimetry assessment, as it is now given, is safe for the investigation of photosensitive patients in optometry clinics where colorimetry equipment is most readily available, but where EEG control is not practical; (2) what proportion of patients with photosensitive epilepsy is likely to benefit to the extent already described in individual cases; (3) whether a tint selected by colorimetry could be shown to reduce the incidence of paroxysmal epileptiform EEG activity in response to flicker and patterns, thereby validating the subjective methods and corroborating the reported seizure reduction. Twenty-four females and nine males (aged 12-43 years) took part. All the patients had suffered visually-provoked seizures, had exhibited a photoparoxysmal response on at least one previous EEG recording, and had received a diagnosis of photosensitive epilepsy. Twenty-two were currently experiencing seizures. A further EEG was recorded in all except seven cases: a routine resting record, followed by hyperventilation. Colorimetry was performed after hyperventilation and before photic stimulation. Twenty-three (70%) reported beneficial effects during colorimetry and were prescribed glasses. There was a preponderance of lenses with a rose or purple colour, in contrast to patients with dyslexia. Seventeen of the 23 patients were available at follow-up, an average of 2.4 years later. Thirteen (57%) reported benefits, and said they were still using the lenses. In six of the 13 the benefits were pronounced, including a reduction of dizziness from fluorescent lighting, elimination of aura when using computer screens etc. Only in three cases was there a reduction in seizures that could reasonably be attributed to the use of lenses; in two of these cases no medications were prescribed, and in the third the medications remained unchanged for four years, two before and two after the introduction of the glasses. In an additional four cases a reduction in seizures was observed but medication had been changed. There was a modest reduction in EEG photosensitivity with the coloured lenses but also to an equivalent or lesser extent with grey in all of the eight patients examined in this way. One patient had seizures during colorimetry, but the seizures were not accompanied by scalp EEG changes. (+info)
Effect of adaptation to telescopic spectacles on the initial human horizontal vestibuloocular reflex.
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Gain of the vestibuloocular reflex (VOR) not only varies with target distance and rotational axis, but can be chronically modified in response to prolonged wearing of head-mounted magnifiers. This study examined the effect of adaptation to telescopic spectacles on the variation of the VOR with changes in target distance and yaw rotational axis for head velocity transients having peak accelerations of 2,800 and 1,000 degrees /s(2). Eye and head movements were recorded with search coils in 10 subjects who underwent whole body rotations around vertical axes that were 10 cm anterior to the eyes, centered between the eyes, between the otoliths, or 20 cm posterior to the eyes. Immediately before each rotation, subjects viewed a target 15 or 500 cm distant. Lighting was extinguished immediately before and was restored after completion of each rotation. After initial rotations, subjects wore 1.9x magnification binocular telescopic spectacles during their daily activities for at least 6 h. Test spectacles were removed and measurement rotations were repeated. Of the eight subjects tolerant of adaptation to the telescopes, six demonstrated VOR gain enhancement after adaptation, while gain in two subjects was not increased. For all subjects, the earliest VOR began 7-10 ms after onset of head rotation regardless of axis eccentricity or target distance. Regardless of adaptation, VOR gain for the proximate target exceeded that for the distant target beginning at 20 ms after onset of head rotation. Adaptation increased VOR gain as measured 90-100 ms after head rotation onset by an average of 0.12 +/- 0.02 (SE) for the higher head acceleration and 0.19 +/- 0.02 for the lower head acceleration. After adaptation, four subjects exhibited significant increases in the canal VOR gain only, whereas two subjects exhibited significant increases in both angular and linear VOR gains. The latencies of linear and early angular target distance effects on VOR gain were unaffected by adaptation. The earliest significant change in angular VOR gain in response to adaptation occurred 50 and 68 ms after onset of the 2,800 and 1,000 degrees /s(2) peak head accelerations, respectively. The latency of the adaptive increase in linear VOR gain was approximately 50 ms for the peak head acceleration of 2,800 degrees /s(2), and 100 ms for the peak head acceleration of 1,000 degrees /s(2). Thus VOR gain changes and latency were consistent with modification in the angular VOR in most subjects, and additionally in the linear VOR in a minority of subjects. (+info)
Effect of spectacles on changes of spherical hypermetropia in infants who did, and did not, have strabismus.
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AIM: To explore why emmetropisation fails in children who have strabismus. METHODS: 289 hypermetropic infants were randomly allocated spectacles and followed. Changes in spherical hypermetropia were compared in those who had strabismus and those who did not. The effect of wearing glasses on these changes was assessed using t tests and regression analysis. RESULTS: Mean spherical hypermetropia decreased in both eyes of "normal" children (p<0.001). The consistent wearing of glasses impeded this process in both eyes (p<0.007). In the children with strabismus, there were no significant changes in either eye, irrespective of treatment (p>0. 05). CONCLUSIONS: In contrast with normal infants, neither eye of those who had strabismus emmetropised, irrespective of whether the incoming vision was clear or blurred. It is suggested that these eyes did not "recognise" the signal of blurred vision, and that they remained long sighted because they were destined to squint. Hence, the children did not squint because they were long sighted, and glasses did not prevent them squinting. (+info)