Numerical modelling of the accommodating lens

Burd, H. J.; Judge, S. J.; Cross, Janelle A.

doi:10.1016/s0042-6989(02)00094-9

Cited by 144 publications

(191 citation statements)

References 26 publications

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“…This could be done by mechanical calculations. Burd et al [8] already included a nucleus in their mechanical model, while preliminary investigations, also based on the finite elements method, have demonstrated that the accommodative amplitude is very sensitive to the relative stiffness of the nucleus [38]. Future research efforts could concentrate on the physiological mechanisms that are responsible for the changes in lens stiffness.…”

Section: Discussionmentioning

confidence: 99%

Stiffness gradient in the crystalline lens

Weeber

Eckert

Pechhold

et al. 2007

Graefes Arch Clin Exp Ophthalmol

141

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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Section: Discussionmentioning

confidence: 99%

Stiffness gradient in the crystalline lens

Weeber

Eckert

Pechhold

et al. 2007

Graefes Arch Clin Exp Ophthalmol

141

147

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“…Subsequent molecular combing studies carried out in our laboratories on isolated microfibrils from vertebrate tissues, however, suggested that the Young's modulus of microfibrils was two orders of magnitude greater (78-96 MPa) than that of elastin (Sherratt et al 2003). From these observations we suggested that fibrillin microfibrils act to reinforce the elastic fibre and that a relatively high Young's modulus allows microfibrils, which comprise the ciliary zonules, to transmit forces between the lens and the ciliary muscle (Burd et al 2002;Sherratt et al 2003). In a subsequent study, Megill and co-workers calculated a stiffness of about 0.9 MPa for the fibrillin-containing elastic fibres in the mesoglea of the hydromedusa Polyorchis penicillatus (Megill et al 2005).…”

Section: Structure and Functionmentioning

confidence: 93%

Tissue elasticity and the ageing elastic fibre

Sherratt

2009

AGE

270

189

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The ability of elastic tissues to deform under physiological forces and to subsequently release stored energy to drive passive recoil is vital to the function of many dynamic tissues. Within vertebrates, elastic fibres allow arteries and lungs to expand and contract, thus controlling variations in blood pressure and returning the pulmonary system to a resting state. Elastic fibres are composite structures composed of a cross-linked elastin core and an outer layer of fibrillin microfibrils. These two components perform distinct roles; elastin stores energy and drives passive recoil, whilst fibrillin microfibrils direct elastogenesis, mediate cell signalling, maintain tissue homeostasis via TGFβ sequestration and potentially act to reinforce the elastic fibre. In many tissues reduced elasticity, as a result of compromised elastic fibre function, becomes increasingly prevalent with age and contributes significantly to the burden of human morbidity and mortality. This review considers how the unique molecular structure, tissue distribution and longevity of elastic fibres pre-disposes these abundant extracellular matrix structures to the accumulation of damage in ageing dermal, pulmonary and vascular tissues. As compromised elasticity is a common feature of ageing dynamic tissues, the development of strategies to prevent, limit or reverse this loss of function will play a key role in reducing age-related morbidity and mortality.

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“…Most parameters needed for the sketches of the lenses were obtained or calculated from information available in the literature (4,5,12,25,28). Stepwise description of the construction from the available data is shown below.…”

Section: Calculation Of Volumes On the Theoretical Human Lensmentioning

confidence: 99%

Volume change of the ocular lens during accommodation

Gerometta¹,

Zamudio²,

Escobar³

et al. 2007

American Journal of Physiology-Cell Physiology

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tion, mammalian lenses change shape from a rounder configuration (near focusing) to a flatter one (distance focusing). Thus the lens must have the capacity to change its volume, capsular surface area, or both. Because lens topology is similar to a torus, we developed an approach that allows volume determination from the lens cross-sectional area (CSA). The CSA was obtained from photographs taken perpendicularly to the lenticular anterior-posterior (A-P) axis and computed with software. We calculated the volume of isolated bovine lenses in conditions simulating accommodation by forcing shape changes with a custom-built stretching device in which the ciliary body-zonulae-lens complex (CB-Z-L) was placed. Two measurements were taken (CSA and center of mass) to calculate volume. Mechanically stretching the CB-Z-L increased the equatorial length and decreased the A-P length, CSA, and lens volume. The control parameters were restored when the lenses were stretched and relaxed in an aqueous physiological solution, but not when submerged in oil, a condition with which fluid leaves the lens and does not reenter. This suggests that changes in lens CSA previously observed in humans could have resulted from fluid movement out of the lens. Thus accommodation may involve changes not only in capsular surface but also in volume. Furthermore, we calculated theoretical volume changes during accommodation in models of human lenses using published structural parameters. In conclusion, we suggest that impediments to fluid flow between the aquaporin-rich lens fibers and the lens surface could contribute to the aging-related loss of accommodative power.lens volume calculation; intralenticular fluid movement; presbyopia; mammalian lens THE EYE IS ABLE TO FORM a clear image on the retina from objects situated within a wide range of distances due to a process called accommodation. In higher vertebrates, including humans, accommodation results from changes in crystalline lens shape and surface radii of curvature (13).When the ciliary muscle is relaxed and flattened against the sclera, the zonulae adjoining the ciliary body and the lens capsule are under tension and thus pulling eccentrically on the lens equator. This action causes the lens to adopt a relatively flattened shape with a larger equatorial diameter and a shorter A-P length, which allows focusing on virtual infinity (zero accommodation). When an individual focuses on a near object, the ciliary muscle contracts (shortening its distance to the lens equator), the zonulae relax, and the lens as a whole adopts a relatively rounded shape, which is its normal tendency. Physically, these changes in lens shape inevitably must involve changes in either capsular surface area or lens volume, or both.Classic theories of lenticular accommodation suggest that the volume of the intraocular crystalline lens remains constant during the accommodation process (16,17,30). No empirical studies have demonstrated that the volume actually stays constant. Because of the physical principle mentioned abov...

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Numerical modelling of the accommodating lens

Cited by 144 publications

References 26 publications

Stiffness gradient in the crystalline lens

Stiffness gradient in the crystalline lens

Tissue elasticity and the ageing elastic fibre

Volume change of the ocular lens during accommodation

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