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Mechanical Characterization of a Con...

Wang, Wei.

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Mechanical Characterization of a Convex Hydrogel Shell (Contact Lens) with Meridional Thickness Variation.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Mechanical Characterization of a Convex Hydrogel Shell (Contact Lens) with Meridional Thickness Variation./
Author:	Wang, Wei.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2017,
Description:	66 p.
Notes:	Source: Masters Abstracts International, Volume: 56-04.
Contained By:	Masters Abstracts International56-04(E).
Subject:	Biomechanics. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10260805
ISBN:	9781369806199

Mechanical Characterization of a Convex Hydrogel Shell (Contact Lens) with Meridional Thickness Variation.
Wang, Wei.

Mechanical Characterization of a Convex Hydrogel Shell (Contact Lens) with Meridional Thickness Variation. - Ann Arbor : ProQuest Dissertations & Theses, 2017 - 66 p.

Source: Masters Abstracts International, Volume: 56-04.

Thesis (M.S.)--Northeastern University, 2017.

To correct myopic and hyperopic vision, disposable hydrogel contact lenses are worn in intimate contact with the cornea of the human eye. The thin lens geometry is designed with one side matching the cornea curvature, while the opposite side is shaped to provide a corrective optical power, d, measured in diopters, D. Lenses with d = 0D are of uniform thickness and can be adopted as the baseline of the mechanical test. Myopic lenses having negative optical powers (--12D < d < 0) are thinnest at the optical axis and thicken along the meridional direction---acting like concave lenses. Conversely, hyperopic lenses having positive optical powers (0 < d < +12D) are thickest at the apex and thins out along the meridian. The degree of comfort experienced by users depends significantly on the mechanical compliance of the lens when it is mechanically deformed during daily use (e.g. blinking). It is the goal of this thesis to characterize lenses with a range of optical power. A sample lens with concave-side down resting on a rigid substrate is subject to a central load along the optical axis. The mechanical response of the applied load, F, as a function of the vertical displacement, y0, is measured by a nano-force mechanical tester, while the deformed geometry y( r, theta, &phis;) is captured by a side-view camera. Cyclic loading shows two distinct features of the lenses: (i) F(y0) and y depending predominantly on the meridional thickness variation; and (ii) significant loading--unloading hysteresis indicating the influx/efflux of the aqueous isotonic solution into/out of the hydrogel matrix. Hyperopic lenses show the least mechanical compliance, and therefore the least degree of comfort in comparison with myopic lenses, even though they are made from the same material. Additional mechanical tests are performed to measure the threshold load to trigger buckling or "flip-flop" of the lens. In addition to their implications for wearing comfort, these phenomena should provide new insights into mechanics of plate and shell, wherein the mechanical behavior of shells with variational thickness has received limited attention in the literature.

ISBN: 9781369806199Subjects--Topical Terms:

548685
Biomechanics.

Mechanical Characterization of a Convex Hydrogel Shell (Contact Lens) with Meridional Thickness Variation.
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245 1 0 $a Mechanical Characterization of a Convex Hydrogel Shell (Contact Lens) with Meridional Thickness Variation.
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300 $a 66 p.
500 $a Source: Masters Abstracts International, Volume: 56-04.
500 $a Adviser: Kai-tak Wan.
502 $a Thesis (M.S.)--Northeastern University, 2017.
520 $a To correct myopic and hyperopic vision, disposable hydrogel contact lenses are worn in intimate contact with the cornea of the human eye. The thin lens geometry is designed with one side matching the cornea curvature, while the opposite side is shaped to provide a corrective optical power, d, measured in diopters, D. Lenses with d = 0D are of uniform thickness and can be adopted as the baseline of the mechanical test. Myopic lenses having negative optical powers (--12D < d < 0) are thinnest at the optical axis and thicken along the meridional direction---acting like concave lenses. Conversely, hyperopic lenses having positive optical powers (0 < d < +12D) are thickest at the apex and thins out along the meridian. The degree of comfort experienced by users depends significantly on the mechanical compliance of the lens when it is mechanically deformed during daily use (e.g. blinking). It is the goal of this thesis to characterize lenses with a range of optical power. A sample lens with concave-side down resting on a rigid substrate is subject to a central load along the optical axis. The mechanical response of the applied load, F, as a function of the vertical displacement, y0, is measured by a nano-force mechanical tester, while the deformed geometry y( r, theta, &phis;) is captured by a side-view camera. Cyclic loading shows two distinct features of the lenses: (i) F(y0) and y depending predominantly on the meridional thickness variation; and (ii) significant loading--unloading hysteresis indicating the influx/efflux of the aqueous isotonic solution into/out of the hydrogel matrix. Hyperopic lenses show the least mechanical compliance, and therefore the least degree of comfort in comparison with myopic lenses, even though they are made from the same material. Additional mechanical tests are performed to measure the threshold load to trigger buckling or "flip-flop" of the lens. In addition to their implications for wearing comfort, these phenomena should provide new insights into mechanics of plate and shell, wherein the mechanical behavior of shells with variational thickness has received limited attention in the literature.
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