Model of the accommodative mechanism in the human eye

Koretz, Jane F.; Handelman, G. H.

doi:10.1016/0042-6989(82)90028-1

Cited by 78 publications

(31 citation statements)

References 15 publications

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“…Coleman 1970;Koretz and Handelman 1982), but at that time this view did not gain much acceptance within the ophthalmologic community. If we follow the evidences listed above and propose that the zonular apparatus is arranged in such a way that the resultant of the tensile forces is directed at some angle posteriorly to the equatorial plane, the role of vitreous cannot be omitted, or otherwise, the process of accommodation would contradict experimental observations (Svetlova and Koshitz 2001).…”

Section: Introductionmentioning

confidence: 92%

Aspects of eye accommodation evaluated by finite elements

Ljubimova

Eriksson

Bauer

2007

Biomech Model Mechanobiol

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Axisymmetric nonlinear finite models of accommodation incorporating the posteriorly sloped force and vitreous effects have been studied by means of their effectiveness in mechanical and optical performances. All materials were assumed to be linearly elastic, vitreous and lens matrices were incompressible. The present model is subjected to certain indicated shortcomings, however, the behavior of the model is predictable, reasonable and favourably consistent with different published data, supporting the Helmholtz theory of accommodation.

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Section: Introductionmentioning

confidence: 92%

Aspects of eye accommodation evaluated by finite elements

Ljubimova

Eriksson

Bauer

2007

Biomech Model Mechanobiol

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“…The young and soft crystalline lens is easy to deform, while the old lens is stiff, hard and unable to be deformed [3,18,31,32]. While some authors represent the stiffness of the lens using a single value for the whole lens [2,24], e.g. the Young's modulus, it has been shown that the stiffness of the lens varies, depending on the location within the lens where stiffness is measured [20].…”

Section: Introductionmentioning

confidence: 99%

Stiffness gradient in the crystalline lens

Weeber

Eckert

Pechhold

et al. 2007

Graefes Arch Clin Exp Ophthalmol

140

147

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Background While the overall stiffness of the lens has been measured in a number of studies, the knowledge about the stiffness distribution within the lens is still limited. The purpose of this study was to determine the stiffness gradient in the human crystalline lens. A secondary purpose was to determine whether the stiffness gradient depends on age. Methods The local dynamic stiffness was measured in 10 human crystalline lenses (age range: 19 to 78 years). The lenses were stored at −70°C before being measured. The influence of freezing on the mechanical properties has been determined in a previous study. A small oscillating probe was used to measure the local dynamic shear modulus as a measure of lens stiffness. The measurements were taken in the cross-sectional plane through the lens equator. Results The local dynamic shear modulus varied with location for all tested lenses. The central stiffness of the oldest lens (78 years) was 10 4 times higher than the youngest (19 years) lens. The equatorial stiffness of the oldest lens was 10 2 times higher than the youngest lens. For the older lenses, the centre was 5.8-210 times stiffer than the periphery, as opposed to earlier results described by Fisher (1971), who found that the periphery was up to 3 times softer than the centre for lenses younger than 70-years-old. For the three youngest lenses (19 to 49 years), the periphery was 2.2-16.6 times stiffer than the centre. Conclusions The dynamic stiffness of the crystalline lens varies with location within the lens. The stiffness gradient depends on the age of the lens. The results of the 10 lenses indicate that the stiffness of both centre and periphery increase with age, but at a different rate.

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“…The pathophysiology of presbyopia is multifactorial, involving age-related anatomical and physiological changes in the choroid, ciliary body, vitreous, lens capsule, and lens fibers. [14][15][16][17][18][19] Although the exact extent to which each of these tissues contributes to presbyopia is unknown, it is commonly accepted that age-related changes in the lens might play a major role in presbyopia. The human lens increases in size (volume) and modulus with advancing age.…”

Section: Introductionmentioning

confidence: 99%

Refilling of Ocular Lens Capsule with Copolymeric Hydrogel Containing Reversible Disulfide

2004

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Polymer solutions can fill any potential irregular cavity using minimally invasive techniques and thus have potential uses in ophthalmology. We prepared acrylamide hydrogels containing disulfide bonds by free radical polymerization in aqueous ethanol. The hydrogels were liquefied using dithiothreitol to yield water-soluble acrylamide copolymers containing pendant thiol (-SH) groups. The weight average molecular weights of the copolymers ranged from 1.43 x 10(5) to 9.22 x 10(5) daltons by GPC. Ellman's analysis and Raman spectroscopy confirmed the presence of -SH. The aqueous solutions of these purified thiol-containing copolymers were oxidized with 3,3'-dithiodipropionic acid or air to reform the hydrogels. The moduli of the reformed hydrogels ranged from 0.27 to 1.1 kPa depending on concentration and thiol content. Rapid endocapsular gelation yielded optically clear gel within the lens capsular bag. This technique now enables us to validate methods to determine the biomechanics of the lens and its role in accommodation.

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Model of the accommodative mechanism in the human eye

Cited by 78 publications

References 15 publications

Aspects of eye accommodation evaluated by finite elements

Aspects of eye accommodation evaluated by finite elements

Stiffness gradient in the crystalline lens

Refilling of Ocular Lens Capsule with Copolymeric Hydrogel Containing Reversible Disulfide

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