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Astigmatism and eye growth: A study ...

Kee, Chea-su.

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Astigmatism and eye growth: A study on primates.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Astigmatism and eye growth: A study on primates./
作者:	Kee, Chea-su.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2003,
面頁冊數:	181 p.
附註:	Source: Dissertations Abstracts International, Volume: 65-10, Section: B.
Contained By:	Dissertations Abstracts International65-10B.
標題:	Ophthalmology. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3114657
ISBN:	9780496621460

Astigmatism and eye growth: A study on primates.
Kee, Chea-su.

Astigmatism and eye growth: A study on primates. - Ann Arbor : ProQuest Dissertations & Theses, 2003 - 181 p.

Source: Dissertations Abstracts International, Volume: 65-10, Section: B.

Thesis (Ph.D.)--University of Houston, 2003.

This item must not be sold to any third party vendors.

Purpose. Visual experience is important for normal eye growth especially during early infancy. Although astigmatism is prevalent in human infants, little is known about its etiology or its influence on early refractive development. This series of studies was undertaken to determine: (1) the prevalence of astigmatism in normal infant macaque monkeys; (2) if developing monkeys eyes are capable of growing in a way to eliminate optically imposed astigmatism; (3) the effects of optically imposed astigmatism on emmetropization; and (4) the astigmatism associated with experimentally induced spherical ametropias in macaque monkeys. Methods. The subjects were rhesus monkeys ( Macaca mulatta) that were reared with either unrestricted vision/zero-powered lenses (control group) or altered early visual experience (treatment group). Results. Experiment 1: Unlike human infants, infant monkeys showed a low prevalence of astigmatic errors. Experiment 2 : Although cylinder-lens-reared monkeys exhibited a high prevalence of ocular astigmatism, the axis of the induced astigmatism was not appropriate to compensate for the astigmatic error imposed by the treatment lenses. The astigmatism was corneal in nature, bilaterally mirror-symmetric and oblique in axis, and reversible. Experiment 3: Emmetropization in the cylinder-lens-reared monkeys appeared to be directed to one of the two principal meridians associated with the treatment lenses. The shifts in refractive error were mainly axial in nature. Experiment 4: In contrast to control monkeys, the experimental monkeys that had axial ametropias frequently developed significant amounts of astigmatism especially when their eyes exhibited relative hyperopic shifts in refractive error. The characteristics of the accompanying astigmatism were very similar to those found in cylinder-lens-reared monkeys. Conclusions. The low prevalence of astigmatism during early development suggests that astigmatism does not provide an essential cue for vision-dependent eye growth in normal infant primates. There was no evidence that macaque monkeys have an active, visually regulated "sphericalization" mechanism. However, in the presence of significant amounts of astigmatism, there was clear evidence that emmetropization was directed toward one of the two focal planes associated with the astigmatic principal meridians and not the circle of least confusion. The similarities between the astigmatic errors in our experimental monkeys and some astigmatic errors in humans suggest that vision-dependent changes in eye growth may contribute to astigmatism in humans. (Abstract shortened by UMI.).

ISBN: 9780496621460Subjects--Topical Terms:

862704
Ophthalmology.
Subjects--Index Terms:

Astigmatism

Astigmatism and eye growth: A study on primates.
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520 $a Purpose. Visual experience is important for normal eye growth especially during early infancy. Although astigmatism is prevalent in human infants, little is known about its etiology or its influence on early refractive development. This series of studies was undertaken to determine: (1) the prevalence of astigmatism in normal infant macaque monkeys; (2) if developing monkeys eyes are capable of growing in a way to eliminate optically imposed astigmatism; (3) the effects of optically imposed astigmatism on emmetropization; and (4) the astigmatism associated with experimentally induced spherical ametropias in macaque monkeys. Methods. The subjects were rhesus monkeys ( Macaca mulatta) that were reared with either unrestricted vision/zero-powered lenses (control group) or altered early visual experience (treatment group). Results. Experiment 1: Unlike human infants, infant monkeys showed a low prevalence of astigmatic errors. Experiment 2 : Although cylinder-lens-reared monkeys exhibited a high prevalence of ocular astigmatism, the axis of the induced astigmatism was not appropriate to compensate for the astigmatic error imposed by the treatment lenses. The astigmatism was corneal in nature, bilaterally mirror-symmetric and oblique in axis, and reversible. Experiment 3: Emmetropization in the cylinder-lens-reared monkeys appeared to be directed to one of the two principal meridians associated with the treatment lenses. The shifts in refractive error were mainly axial in nature. Experiment 4: In contrast to control monkeys, the experimental monkeys that had axial ametropias frequently developed significant amounts of astigmatism especially when their eyes exhibited relative hyperopic shifts in refractive error. The characteristics of the accompanying astigmatism were very similar to those found in cylinder-lens-reared monkeys. Conclusions. The low prevalence of astigmatism during early development suggests that astigmatism does not provide an essential cue for vision-dependent eye growth in normal infant primates. There was no evidence that macaque monkeys have an active, visually regulated "sphericalization" mechanism. However, in the presence of significant amounts of astigmatism, there was clear evidence that emmetropization was directed toward one of the two focal planes associated with the astigmatic principal meridians and not the circle of least confusion. The similarities between the astigmatic errors in our experimental monkeys and some astigmatic errors in humans suggest that vision-dependent changes in eye growth may contribute to astigmatism in humans. (Abstract shortened by UMI.).
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