Diurnal rhythms and eye growth in chicks.
Item
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Title
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Diurnal rhythms and eye growth in chicks.
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Identifier
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AAI9707136
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identifier
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9707136
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Creator
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Nickla, Debora Lee.
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Contributor
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Adviser: Josh Wallman
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Date
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1996
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Animal Physiology
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Abstract
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To explore the possibility that ocular diurnal rhythms are involved in the regulation of ocular growth and its control by the retina, I examined several ocular rhythms (axial length, choroid thickness, proteoglycan synthesis and intraocular pressure) in normal eyes, form-deprived eyes (which are elongating twice as rapidly as normal), and eyes recovering from deprivation myopia (which have slowed elongation). In addition, I examined the efficacy of visual manipulations on deprivation myopia as a function of time of day.;The principal findings are: (1) Visual manipulations that decrease eye growth are most effective during the night. (2) Eyes in all three conditions show diurnal fluctuations in axial length. In normal and form-deprived eyes, elongation is greatest in the morning and least in the evening. (3) Eyes in all three conditions show diurnal fluctuations in choroidal thickness. In normal and form-deprived eyes, the choroid thins in the morning and thickens in the evening, hence the axial and choroidal rhythms are approximately anti-phase to one another. (4) In recovering eyes, the axial and choroidal rhythms are shifted, so that they are now in phase. (5) Intraocular pressure shows a diurnal rhythm in normal eyes, being high during the day and low at night. This rhythm persists in constant darkness. However, in form-deprived eyes the rhythm becomes desynchronized with respect to the light/dark cycle. (6) The phase difference between the rhythms in axial length and intraocular pressure predicts the rate of ocular growth. (7) There is a diurnal rhythm in proteoglycan synthesis in the sclera, being higher during the day than during the night. This rhythm persists in culture for at least 3 cycles.;We propose that the phase relationships between these rhythms determine the rate of ocular growth. Specifically, we argue first, that the synthesis of scleral extracellular matrix, as reflected by proteoglycan synthesis, is an important correlate of ocular elongation. Second, that it is stimulated by the daily intraocular pressure changes, especially at certain times of day; third, that proteoglycan synthesis is inhibited by daily increases in choroidal thickness, again in a phase-dependent manner.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
