PubMed · 12016188
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Douglas R Fredrick. 2002-05-18. Myopia.. https://doi.org/10.1136/bmj.324.7347.1195
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PURPOSE: To investigate the accommodation-convergence relationship during the incipient phase of presbyopia. The study aimed to differentiate between the current theories of presbyopia and to explore the mechanisms by which the oculomotor system compensates for the change in the accommodation-convergence relationship contingent on a declining amplitude of accommodation. METHODS: Using a Canon R-1 open-view autorefractor and a haploscope device, measurements were made of the stimulus and response accommodative convergence/accommodation ratios and the convergence accommodation/convergence ratio of 28 subjects aged 35-45 years at the commencement of the study. Amplitude of accommodation was assessed using a push-down technique. The measurements were repeated at 4-monthly intervals over a 2-year period. RESULTS: The results showed that with the decline in the amplitude of accommodation there is an increase in the accommodative convergence response per unit of accommodative response and a decrease in the convergence accommodation response per unit of convergence. CONCLUSIONS: The results of this study fail to support the Hess-Gullstrand theory of presbyopia in that the ciliary muscle effort required to produce a unit change in accommodation increases, rather than stays constant, with age. Data show that the near vision response is limited to the maximum vergence response that can be tolerated and, despite being within the amplitude of accommodation, a stimulus may still appear blurred because the vergence component determines the proportion of available accommodation utilised during near vision.
We have measured monocular and binocular contrast sensitivities in response to medium to high spatial frequencies of vertical sinusoidal grating patterns in normal subjects, anisometropic amblyopes, strabismic amblyopes and non-amblyopic esotropes. On binocular viewing, contrast sensitivities were slightly but significantly increased in normal subjects, markedly increased in anisometropes and esotropes with anomalous binocular single vision (BSV) and significantly reduced in esotropes and exotropes without BSV. Application of a prismatic correction to the strabismic eye in order to achieve bifoveal stimulation resulted in a significant reduction in contrast sensitivity in esotropes with and without anomalous BSV, in exotropes and in non-amblyopic esotropes. Control experiments in normal subjects with monocular viewing showed that degradative effects of the prism occurred only with high prism powers and at high spatial frequencies, thus establishing that the reduced contrast sensitivities were the consequence of bifoveal stimulation rather than optical degradation. Displacement of the image of the grating pattern by 2 deg. in normal subjects and anisometropes by a dichoptic method to simulate a small angle esotropia had no effect on the contrast sensitivities recorded through the companion eye. By contrast, esotropes showed similar reductions in contrast sensitivity to those obtained with the prism experiments, confirming a fundamental difference between subjects with normal and abnormal ocular alignments. The results have thus established a suppressive action of the fovea of the amblyopic eye acting on the companion, non-amblyopic eye and indicate that correction of ocular misalignments in adult esotropes may be disadvantageous to binocular visual performance.
Unusual ocular symptoms observed during intravenous treatment with anti-disialoganglioside antibody (Ab) in children suffering from neuroblastoma were analyzed and the results reported. Within the framework of the German Collaborative Neuroblastoma Study NB97, 85 children with high-risk neuroblastoma received anti-GD2 monoclonal antibody ch14.18 intravenously. Side effects were regularly reported to the study center. Ocular symptoms were recorded in clinical detail, duration and development over time. Symptoms of a parasympathetic deficit corresponding to internal ophthalmoplegia, i.e. mydriasis and accommodation deficit, were found in 10 patients. They were uni- or bilateral, began after the termination of Ab infusion and improved or disappeared in all surviving children. They did not reappear or worsen upon repeated Ab infusions. The pathophysiology of these disorders remains poorly understood. It is concluded that during systemic treatment with the anti-GD2 antibody ch14.18, reversible symptoms of parasympathetic denervation of the eye may occur which, however, do not warrant termination of this treatment.