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Davies LN, Biswas S, Bullimore M, Cruickshank F, Estevez JJ, Khanal S, Kollbaum P, Marcotte-Collard R, Montani G, Plainis S, Richdale K, Simard P, Wolffsohn JS. BCLA CLEAR presbyopia: Mechanism and optics. Cont Lens Anterior Eye 2024; 47:102185. [PMID: 38796331 DOI: 10.1016/j.clae.2024.102185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2024]
Abstract
With over a billion adults worldwide currently affected, presbyopia remains a ubiquitous, global problem. Despite over a century of study, the precise mechanism of ocular accommodation and presbyopia progression remains a topic of debate. Accordingly, this narrative review outlines the lenticular and extralenticular components of accommodation together with the impact of age on the accommodative apparatus, neural control of accommodation, models of accommodation, the impact of presbyopia on retinal image quality, and both historic and contemporary theories of presbyopia.
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Affiliation(s)
- Leon N Davies
- School of Optometry, College of Health and Life Sciences, Aston University, Birmingham, UK.
| | - Sayantan Biswas
- School of Optometry, College of Health and Life Sciences, Aston University, Birmingham, UK
| | | | - Fiona Cruickshank
- Division of Pharmacy and Optometry, School of Health Sciences, Faculty of Biology, Medicine and Health, University of Manchester, UK
| | - Jose J Estevez
- Caring Futures Institute, College of Nursing and Health Sciences, Optometry and Vision Science, Flinders University, Adelaide, Australia; Flinders Centre for Ophthalmology, Eye and Vision Research, Department of Ophthalmology, Flinders University, Adelaide, Australia
| | - Safal Khanal
- Department of Optometry and Vision Science, The University of Alabama at Birmingham, USA
| | | | | | | | - Sotiris Plainis
- School of Optometry, College of Health and Life Sciences, Aston University, Birmingham, UK; Laboratory of Optics and Vision, School of Medicine, University of Crete, Greece
| | | | - Patrick Simard
- School of Optometry, Universite de Montreal, Montreal, Quebec, Canada
| | - James S Wolffsohn
- School of Optometry, College of Health and Life Sciences, Aston University, Birmingham, UK
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Schachar RA, Schachar IH, Kumar S, Feldman EI, Pierscionek BK, Cosman PC. Model of zonular forces on the lens capsule during accommodation. Sci Rep 2024; 14:5896. [PMID: 38467700 PMCID: PMC10928188 DOI: 10.1038/s41598-024-56563-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Accepted: 03/08/2024] [Indexed: 03/13/2024] Open
Abstract
How the human eye focuses for near; i.e. accommodates, is still being evaluated after more than 165 years. The mechanism of accommodation is essential for understanding the etiology and potential treatments for myopia, glaucoma and presbyopia. Presbyopia affects 100% of the population in the fifth decade of life. The lens is encased in a semi-elastic capsule with attached ligaments called zonules that mediate ciliary muscle forces to alter lens shape. The zonules are attached at the lens capsule equator. The fundamental issue is whether during accommodation all the zonules relax causing the central and peripheral lens surfaces to steepen, or the equatorial zonules are under increased tension while the anterior and posterior zonules relax causing the lens surface to peripherally flatten and centrally steepen while maintaining lens stability. Here we show with a balloon capsule zonular force model that increased equatorial zonular tension with relaxation of the anterior and posterior zonules replicates the topographical changes observed during in vivo rhesus and human accommodation of the lens capsule without lens stroma. The zonular forces required to simulate lens capsule configuration during in vivo accommodation are inconsistent with the general belief that all the zonules relax during accommodation.
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Affiliation(s)
- Ronald A Schachar
- Department of Physics, University of Texas at Arlington, Arlington, TX, USA.
| | - Ira H Schachar
- North Bay Vitreoretinal Consultants, Santa Rosa, CA, USA
| | - Shubham Kumar
- Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA, USA
| | | | - Barbara K Pierscionek
- Faculty of Health, Medicine and Social Care, Medical Technology Research Centre, Anglia Ruskin University, Chelmsford, UK
| | - Pamela C Cosman
- Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA, USA
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Pu Y, Liu Z, Ye L, Xia Y, Chen X, Wang K, Pierscionek BK. The major influence of anterior and equatorial zonular fibres on the far-to-near accommodation revealed by a 3D pre-stressed model of the anterior eye. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2023; 242:107815. [PMID: 37729794 DOI: 10.1016/j.cmpb.2023.107815] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 09/09/2023] [Accepted: 09/14/2023] [Indexed: 09/22/2023]
Abstract
PURPOSE To explore the synergistic function of the ligaments in eye, the zonular fibres, that mediate change in eye lens shape to allow for focussing over different distances. METHODS A set of 3D Finite Element models of the anterior eye together with a custom developed pre-stress modelling approach was proposed to simulate vision for distant objects (the unaccommodated state) to vision for near objects (accommodation). One of the five zonular groups was cut off in sequence creating five models with different zonular arrangements, the contribution of each zonular group was analysed by comparing results of each specific zonular-cut model with those from the all-zonules model in terms of lens shape and zonular tensions. RESULTS In the all-zonular model, the anterior and equatorial zonules carry the highest tensions. In the anterior zonular-cut model, the equatorial zonular tension increases while the posterior zonular tension decreases, resulting in an increase in the change in Central Optical Power (COP). In the equatorial zonular-cut model, both the anterior and posterior zonular tensions increase, causing a decreasing change in COP. The change in COP decreases only slightly in the other models. For vitreous zonular-cut models, little change was seen in either the zonular tension or the change in COP. CONCLUSIONS The anterior and the equatorial zonular fibres have the major influence on the change in lens optical power, with the anterior zonules having a negative effect and the equatorial zonules contributing a positive effect. The contribution to variations in optical power by the equatorial zonules is much larger than by the posterior zonules.
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Affiliation(s)
- Yutian Pu
- Key Laboratory for Biomechanics and Mechanobiology of Ministry for Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine and School of Biological Science and Medical Engineering, Beihang University, Beijing, China
| | - Ziyuan Liu
- Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, Beijing, China
| | - Lin Ye
- Faculty of Health, Education, Medicine and Social Care, Medical Technology Research Centre, Anglia Ruskin University, Bishops Hall Lane, Chelmsford, United Kingdom
| | - Yunxin Xia
- Key Laboratory for Biomechanics and Mechanobiology of Ministry for Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine and School of Biological Science and Medical Engineering, Beihang University, Beijing, China
| | - Xiaoyong Chen
- Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, Beijing, China
| | - Kehao Wang
- Key Laboratory for Biomechanics and Mechanobiology of Ministry for Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine and School of Biological Science and Medical Engineering, Beihang University, Beijing, China.
| | - Barbara K Pierscionek
- Faculty of Health, Education, Medicine and Social Care, Medical Technology Research Centre, Anglia Ruskin University, Bishops Hall Lane, Chelmsford, United Kingdom
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Schachar RA, Schachar IH, Pu Y, Kumar S, Cosman PC, Pierscionek BK, Wang K. Finite element analysis of zonular forces. Exp Eye Res 2023; 237:109709. [PMID: 37923162 DOI: 10.1016/j.exer.2023.109709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 10/28/2023] [Accepted: 10/30/2023] [Indexed: 11/07/2023]
Abstract
To determine the effect of zonular forces on lens capsule topography, a finite element (FE) analyses of lens capsules with no lens stroma and constant and variable thickness with anterior capsulotomies of 1.5 mm-6.5 mm were evaluated when subjected to equatorial (Ez), anterior (Az) and posterior (Pz) zonular forces. The lens capsule was considered in the unaccommodated state when the total initial zonular force was 0.00075 N or 0.3 N. From the total 0.00075 N zonular force, the Ez force was increased in 0.000125 N steps for a maximum force of 0.03 N and simultaneously the Az plus Pz force was reduced in 0.000125 N steps to zero. In addition, the force of all the zonules was reduced from 0.00075 N and separately from 0.3 N in 0.000125 N steps to zero. Only when Ez force was increased as Az and Pz force was reduced did the capsule topography simulate in vivo observations with the posterior capsule pole bowing posteriorly. The posterior bowing was directly related to Ez force and capsulotomy size. Whether the total force of all the zonules in the unaccommodated state was 0.00075 N or 0.3 N and reduced in steps to zero, the lens capsule topography did not emulate the in vivo observations. The FE analysis demonstrated that Ez tension increases while the Az and Pz tension decreases and that all the zonules do not relax during ciliary muscle contraction.
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Affiliation(s)
- Ronald A Schachar
- Department of Physics, University of Texas at Arlington, Arlington, TX, 76019, USA.
| | - Ira H Schachar
- North Bay Vitreoretinal Consultants, Santa Rosa, CA, 95403, USA
| | - Yutian Pu
- Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine, Beihang University, Beijing, 100191, China
| | - Shubham Kumar
- Department of Electrical and Computer Engineering, University of California San Diego, San Diego, CA, 92093, USA
| | - Pamela C Cosman
- Department of Electrical and Computer Engineering, University of California San Diego, San Diego, CA, 92093, USA
| | - Barbara K Pierscionek
- Faculty of Health, Medicine and Social Care, Medical Technology Research Centre, Anglia Ruskin University, Chelmsford, CM1 1SQ, UK
| | - Kehao Wang
- Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine, Beihang University, Beijing, 100191, China
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Characterisation and Modelling of an Artificial Lens Capsule Mimicking Accommodation of Human Eyes. Polymers (Basel) 2021; 13:polym13223916. [PMID: 34833214 PMCID: PMC8619262 DOI: 10.3390/polym13223916] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Revised: 10/29/2021] [Accepted: 11/03/2021] [Indexed: 11/17/2022] Open
Abstract
A synthetic material of silicone rubber was used to construct an artificial lens capsule (ALC) in order to replicate the biomechanical behaviour of human lens capsule. The silicone rubber was characterised by monotonic and cyclic mechanical tests to reveal its hyper-elastic behaviour under uniaxial tension and simple shear as well as the rate independence. A hyper-elastic constitutive model was calibrated by the testing data and incorporated into finite element analysis (FEA). An experimental setup to simulate eye focusing (accommodation) of ALC was performed to validate the FEA model by evaluating the shape change and reaction force. The characterisation and modelling approach provided an insight into the intrinsic behaviour of materials, addressing the inflating pressure and effective stretch of ALC under the focusing process. The proposed methodology offers a virtual testing environment mimicking human capsules for the variability of dimension and stiffness, which will facilitate the verification of new ophthalmic prototype such as accommodating intraocular lenses (AIOLs).
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Hirota M, Morimoto T, Miyoshi T, Fujikado T. Simultaneous Measurement of Objective and Subjective Accommodation in Response to Step Stimulation. Invest Ophthalmol Vis Sci 2020; 61:38. [PMID: 33252633 PMCID: PMC7705395 DOI: 10.1167/iovs.61.13.38] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose This study aimed to evaluate differences in objective and subjective accommodation dynamically and simultaneously. Methods Thirty-four pre-presbyopic healthy volunteers (mean age ± SD, 41.0 ± 3.2 years) participated in this study. Initially, the reaction time for detecting a change in the target was measured at near. Dynamic accommodation was then monocularly recorded using an open-view Shack-Hartmann aberrometer and compared with the amplitude and velocity of subjective accommodation. Results The objective amplitude of accommodation (0.97 ± 0.32 diopter [D]) was significantly greater than the subjective amplitude of accommodation (0.62 ± 0.43 D; P < 0.001). The accommodative velocity was significantly faster for the "before the accommodation" response time (0.47 ± 0.38 D/s) than the "after the accommodation" response time (0.21 ± 0.22 D/s; P = 0.007). Conclusions The human eye under the monocular condition quickly adjusts to the focal plane to clearly archive the nearby object, and the focal plane thereafter is slowly and accurately adjusted to the visual target after visual recognition.
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Affiliation(s)
- Masakazu Hirota
- Department of Applied Visual Science, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan.,Department of Orthoptics, Faculty of Medical Technology, Teikyo University, Itabashi, Tokyo, Japan
| | - Takeshi Morimoto
- Department of Applied Visual Science, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan.,Department of Advanced Visual Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
| | - Tomomitsu Miyoshi
- Department of Integrative Physiology, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
| | - Takashi Fujikado
- Department of Applied Visual Science, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan.,Special Research Promotion Group, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
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7
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The importance of parameter choice in modelling dynamics of the eye lens. Sci Rep 2017; 7:16688. [PMID: 29192148 PMCID: PMC5709469 DOI: 10.1038/s41598-017-16854-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 11/18/2017] [Indexed: 11/08/2022] Open
Abstract
The lens provides refractive power to the eye and is capable of altering ocular focus in response to visual demand. This capacity diminishes with age. Current biomedical technologies, which seek to design an implant lens capable of replicating the function of the biological lens, are unable as yet to provide such an implant with the requisite optical quality or ability to change the focussing power of the eye. This is because the mechanism of altering focus, termed accommodation, is not fully understood and seemingly conflicting theories require experimental support which is difficult to obtain from the living eye. This investigation presents finite element models of the eye lens based on data from human lenses aged 16 and 35 years that consider the influence of various modelling parameters, including material properties, a wide range of angles of force application and capsular thickness. Results from axisymmetric models show that the anterior and posterior zonules may have a greater impact on shape change than the equatorial zonule and that choice of capsular thickness values can influence the results from modelled simulations.
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8
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Mechanism of accommodation assessed by change in precisely registered ocular images associated with concurrent change in auto-refraction. Graefes Arch Clin Exp Ophthalmol 2017; 256:395-402. [PMID: 29147767 DOI: 10.1007/s00417-017-3843-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 09/27/2017] [Accepted: 11/04/2017] [Indexed: 10/18/2022] Open
Abstract
PURPOSE Our purpose was to determine the changes in anterior chamber depth (ACD) and central lens thickness (CLT) during pharmacologically induced accommodation. METHODS Following pupillary dilation with phenylephrine 10%, baseline auto-refractions and swept-source optical coherence tomographic biometric images (Zeiss IOLMaster 700) were obtained from the right eyes of 25 subjects aged 19 to 24 years. Pilocarpine 4% and phenylephrine 10% were then instilled into these right eyes. One hour later, auto-refractions and biometric imaging were repeated. Only data from eight of 25 subjects met the following stringent criteria to be included in the study analysis: pre and post-pilocarpine biometric foveal images were registerable, the images of the corneal centers were shifted by ≤100 μm, pupils >5 mm and the pharmacologically induced refractive change was ≥ -7 diopters. RESULTS The mean auto-refractive accommodative change for the eight included subjects was -12.45 diopters (± 3.45 diopters). The mean change in CLT was 81 μm (± 54 μm) and the mean change in ACD was -145 μm (± 86 μm). Superimposition of the registered pre and post-pilocarpine biometric images of the sagittal sections of the whole eye from each subject demonstrated that the position of the whole lens did not shift either anteriorly, posteriorly or vertically during pharmacologically induced accommodation. CONCLUSIONS A small increase in lens thickness was associated with a large change in accommodative amplitude and no significant change in lens position as predicted by the Schachar theory.
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Schachar RA, Mani M, Schachar IH. Image registration reveals central lens thickness minimally increases during accommodation. Clin Ophthalmol 2017; 11:1625-1636. [PMID: 28979092 PMCID: PMC5602687 DOI: 10.2147/opth.s144238] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Purpose To evaluate anterior chamber depth, central crystalline lens thickness and lens curvature during accommodation. Setting California Retina Associates, El Centro, CA, USA. Design Healthy volunteer, prospective, clinical research swept-source optical coherence biometric image registration study of accommodation. Methods Ten subjects (4 females and 6 males) with an average age of 22.5 years (range: 20–26 years) participated in the study. A 45° beam splitter attached to a Zeiss IOLMaster 700 (Carl Zeiss Meditec Inc., Jena, Germany) biometer enabled simultaneous imaging of the cornea, anterior chamber, entire central crystalline lens and fovea in the dilated right eyes of subjects before, and during focus on a target 11 cm from the cornea. Images with superimposable foveal images, obtained before and during accommodation, that met all of the predetermined alignment criteria were selected for comparison. This registration requirement assured that changes in anterior chamber depth and central lens thickness could be accurately and reliably measured. The lens radii of curvatures were measured with a pixel stick circle. Results Images from only 3 of 10 subjects met the predetermined criteria for registration. Mean anterior chamber depth decreased, −67 μm (range: −0.40 to −110 μm), and mean central lens thickness increased, 117 μm (range: 100–130 μm). The lens surfaces steepened, anterior greater than posterior, while the lens, itself, did not move or shift its position as appeared from the lack of movement of the lens nucleus, during 7.8 diopters of accommodation, (range: 6.6–9.7 diopters). Conclusion Image registration, with stable invariant references for image correspondence, reveals that during accommodation a large increase in lens surface curvatures is associated with only a small increase in central lens thickness and no change in lens position.
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Affiliation(s)
- Ronald A Schachar
- Department of Physics, University of Texas at Arlington, Arlington, TX
| | | | - Ira H Schachar
- Byers Eye Institute of Stanford University, Palo Alto, CA, USA
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10
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David G, Pedrigi RM, Humphrey JD. Accommodation of the human lens capsule using a finite element model based on nonlinear regionally anisotropic biomembranes. Comput Methods Biomech Biomed Engin 2016; 20:302-307. [PMID: 27609339 DOI: 10.1080/10255842.2016.1228907] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Accommodation of the eyes, the mechanism that allows humans to focus their vision on near objects, naturally diminishes with age via presbyopia. People who have undergone cataract surgery, using current surgical methods and artificial lens implants, are also left without the ability to accommodate. The process of accommodation is generally well known; however the specific mechanical details have not been adequately explained due to difficulties and consequences of performing in vivo studies. Most studies have modeled the mechanics of accommodation under assumptions of a linearly elastic, isotropic, homogenous lens and lens capsule. Recent experimental and numerical studies showed that the lens capsule exhibits nonlinear elasticity and regional anisotropy. In this paper we present a numerical model of human accommodation using a membrane theory based finite element approach, incorporating recent findings on capsular properties. This study seeks to provide a novel perspective of the mechanics of accommodation. Such findings may prove significant in seeking biomedical solutions to restoring loss of visual power.
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Affiliation(s)
- G David
- a Institute of Mathematics , University of the Philippines , Quezon City , Philippines
| | - R M Pedrigi
- b Department of Bioengineering , Imperial College London , London , UK
| | - J D Humphrey
- c Department of Biomedical Engineering , Yale University , New Haven , CT , USA
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11
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Wang K, Venetsanos D, Wang J, Pierscionek BK. Gradient moduli lens models: how material properties and application of forces can affect deformation and distributions of stress. Sci Rep 2016; 6:31171. [PMID: 27507665 PMCID: PMC4979009 DOI: 10.1038/srep31171] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 07/13/2016] [Indexed: 11/11/2022] Open
Abstract
The human lens provides one-third of the ocular focussing power and is responsible for altering focus over a range of distances. This ability, termed accommodation, defines the process by which the lens alters shape to increase or decrease ocular refractive power; this is mediated by the ciliary muscle through the zonule. This ability decreases with age such that around the sixth decade of life it is lost rendering the eye unable to focus on near objects. There are two opponent theories that provide an explanation for the mechanism of accommodation; definitive support for either of these requires investigation. This work aims to elucidate how material properties can affect accommodation using Finite Element models based on interferometric measurements of refractive index. Gradients of moduli are created in three models from representative lenses, aged 16, 35 and 48 years. Different forms of zonular attachments are studied to determine which may most closely mimic the physiological form by comparing stress and displacement fields with simulated shape changes to accommodation in living lenses. The results indicate that for models to mimic accommodation in living eyes, the anterior and posterior parts of the zonule need independent force directions. Choice of material properties affects which theory of accommodation is supported.
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Affiliation(s)
- Kehao Wang
- Faculty of Science Engineering and Computing, Penrhyn Road, KT1 2EE, Kingston-upon-Thames, UK
| | - Demetrios Venetsanos
- Faculty of Science Engineering and Computing, Penrhyn Road, KT1 2EE, Kingston-upon-Thames, UK
| | - Jian Wang
- Faculty of Science Engineering and Computing, Penrhyn Road, KT1 2EE, Kingston-upon-Thames, UK
| | - Barbara K Pierscionek
- Faculty of Science Engineering and Computing, Penrhyn Road, KT1 2EE, Kingston-upon-Thames, UK
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12
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Ovenseri-Ogbomo GO, Oduntan OA. Mechanism of accommodation: A review of theoretical propositions. AFRICAN VISION AND EYE HEALTH 2015. [DOI: 10.4102/aveh.v74i1.28] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Accommodation is the process by which the human eye changes its focus to see objects at varying distances from the eye. For nearly 300 years, scientists have investigated and presented various views on the mechanism of accommodation. The purpose of this review is to present both the historical and contemporary theories that underpin the process of accommodation. Keywords such as ocular accommodation, mechanism of accommodation and accommodative mechanism were used to retrieve published material on the subject. Classical propositions by Thomas Young and Hermann von Helmholtz, amongst others, are presented.
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13
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Zhou XY, Wang L, Zhou XT, Yu ZQ. Wavefront aberration changes caused by a gradient of increasing accommodation stimuli. Eye (Lond) 2014; 29:115-21. [PMID: 25341432 DOI: 10.1038/eye.2014.244] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 09/02/2014] [Indexed: 12/16/2022] Open
Abstract
PURPOSE The aim of this study was to investigate the wavefront aberration changes in human eyes caused by a gradient of increasing accommodation stimuli. DESIGN This is a prospective, single-site study. METHODS Healthy volunteers (n=22) aged 18-28 years whose refraction states were emmetropia or mild myopia, with astigmatism <1 diopter (D), were included in this study. After dilating the right pupil with 0.5% phenylephrine drops, the wavefront aberration of the right eye was measured continuously either without or with 1, 2, 3, 4, 5, or 6D accommodation stimuli (WFA1000B psychophysical aberrometer). The root mean square (RMS) values of the total wavefront aberrations, higher-order aberrations, and 35 individual Zernike aberrations under different accommodation stimuli were calculated and compared. RESULTS The average induced accommodations using 1, 2, 3, 4, 5, or 6D accommodation stimuli were 0.848, 1.626, 2.375, 3.249, 4.181, or 5.085 D, respectively. The RMS of total wavefront aberrations, as well as higher-order aberrations, showed no significant effects with 1-3 D accommodation stimuli, but increased significantly under 4, 5, and 6 D accommodation stimuli compared with relaxed accommodation. Zernike coefficients of significantly decreased with increasing levels of accommodation. CONCLUSION Higher-order wavefront aberrations in human eyes changed with increased accommodation. These results are consistent with Schachar's accommodation theory.
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Affiliation(s)
- X-Y Zhou
- Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, China
| | - L Wang
- Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, China
| | - X-T Zhou
- 1] Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, China [2] Key Laboratory of Myopia, Ministry of Health, Shanghai, China
| | - Z-Q Yu
- 1] Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, China [2] Key Laboratory of Myopia, Ministry of Health, Shanghai, China
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14
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Giovanzana S, Schachar RA, Talu S, Kirby RD, Yan E, Pierscionek BK. Evaluation of equations for describing the human crystalline lens. JOURNAL OF MODERN OPTICS 2013. [DOI: 10.1080/09500340.2013.782432] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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15
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Schachar RA. Finite element analysis and the Schachar mechanism of accommodation. J Cataract Refract Surg 2011; 37:979. [PMID: 21511174 DOI: 10.1016/j.jcrs.2011.03.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2011] [Indexed: 11/19/2022]
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16
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Pedrigi RM, Humphrey JD. Computational model of evolving lens capsule biomechanics following cataract-like surgery. Ann Biomed Eng 2010; 39:537-48. [PMID: 20665113 DOI: 10.1007/s10439-010-0133-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Accepted: 07/14/2010] [Indexed: 10/19/2022]
Abstract
Cataract surgery is an invasive procedure whereby lens fibers are removed through a permanent central hole, or capsulorhexis, in the surrounding lens capsule and replaced with an artificial intraocular lens (IOL). Remnant lens epithelial cells subsequently transdifferentiate to a more contractile and synthetic wound-healing phenotype, which causes significant structural and mechanical adaptations of the residual lens capsule. The goal of this study is to present a computational model capable of capturing salient features of the biomechanical evolution of the lens capsule following cataract-like surgery. The model is shown to predict marked long-term increases in thickness and stiffness of the lens capsule nearest the edge of the capsulorhexis comparable to reported measurements. Such models represent a first step toward understanding better the long-term interactions between the residual lens capsule and implanted IOL, thus initiating a new paradigm for the design of improved IOLs, including those having an accommodative feature.
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Affiliation(s)
- R M Pedrigi
- Department of Bioengineering, Royal School of Mines, Imperial College London, London, SW7 2AZ, UK.
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Pedrigi R, Dziezyc J, Humphrey J. Altered mechanical behavior and properties of the human anterior lens capsule after cataract surgery. Exp Eye Res 2009; 89:575-80. [DOI: 10.1016/j.exer.2009.06.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2009] [Revised: 05/26/2009] [Accepted: 06/02/2009] [Indexed: 11/27/2022]
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Abstract
Debate regarding the mechanisms of how the eye changes focus (accommodation) and why this ability is lost with age (presbyopia) has recently been rejoined due to the advent of surgical procedures for the correction of presbyopia. Due to inherent confounding factors in both in vivo and in vitro measurement techniques, mechanical modeling of the behavior of the ocular lens in accommodation has been attempted to settle the debate. However, a paucity of reliable mechanical property measurements has proven problematic in the development of a successful mechanical model of accommodation. Instrumented microindentation was utilized to directly measure the local elastic modulus and dynamic response at various locations in the lens. The young porcine lens exhibits a large modulus gradient with the highest modulus appearing at the center of the nucleus and exponentially decreasing with distance. The loss tangent was significantly higher in the decapsulated lens and the force waveform amplitude decreased significantly upon removal of the lens capsule. The findings indicate that localized measurements of the lens’ mechanical properties are necessary to achieve accurate quantitative parameters suitable for mechanical modeling efforts. The results also indicate that the lens behaves as a crosslinked gel rather than as a collection of individual arched fiber cells.
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Affiliation(s)
- Matthew Reilly
- Department of Veterans Affairs, 915 North Grand Boulevard, St. Louis, MO 63106; Department of Energy, Environmental, and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63110
| | - Nathan Ravi
- Department of Veterans Affairs, 915 North Grand Boulevard, St. Louis, MO 63106; Department of Energy, Environmental, and Chemical Engineering, and Department of Ophthalmology and Visual Sciences, Washington University in St. Louis, St. Louis, MO 63110
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19
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Schachar RA, Fygenson DK. Topographical changes of biconvex objects during equatorial traction: an analogy for accommodation of the human lens. Br J Ophthalmol 2007; 91:1698-703. [PMID: 16837546 PMCID: PMC2095551 DOI: 10.1136/bjo.2006.094888] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/13/2006] [Indexed: 11/03/2022]
Abstract
AIM To assess and compare the changes in shape of encapsulated biconvex structures undergoing equatorial traction with those changes reported in the human lens during accommodation. METHODS Equatorial traction was applied to several different biconvex structures: air, water, and gel filled mylar and rubber balloons and spherical vesicles. In the vesicles, traction was applied externally, using optical tweezers, or from within, by the assembly of encapsulated microtubules. The shape changes were recorded photographically and the change in central radius of curvature of water filled mylar balloons was quantified. RESULTS Whenever an outward equatorial force was applied to the long axis of long oval biconvex objects, where the minor to major axis ratio was =0.6, the central surfaces steepened and the peripheral surfaces flattened. Similar changes in the shape of the lens have been reported during human in vivo accommodation. CONCLUSIONS All biconvex structures that have been studied demonstrate similar shape changes in response to equatorial traction. This effect is independent of capsular thickness. The consistent observation of this physical change in the configuration of biconvex structures in response to outward equatorial force suggests that this may be a universal response of biconvex structures, also applicable to the human lens undergoing accommodation.
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Affiliation(s)
- R A Schachar
- Department of Physics, University of Texas at Arlington, Arlington, Texas, USA.
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20
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Pedrigi RM, David G, Dziezyc J, Humphrey JD. Regional mechanical properties and stress analysis of the human anterior lens capsule. Vision Res 2007; 47:1781-9. [PMID: 17467027 DOI: 10.1016/j.visres.2007.03.014] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2006] [Revised: 01/25/2007] [Indexed: 10/23/2022]
Abstract
The lens capsule of the eye functions, in part, as a deformable support through which the ciliary body applies tractions that can alter lens curvature and corresponding refractive power during the process of accommodation. Although it has long been recognized that characterization of the mechanical properties of the lens capsule is fundamental to understanding this physiologic process as well as clinical interventions, prior data have been limited by one-dimensional testing of excised specimens despite the existence of multiaxial loading in vivo. In this paper, we employ a novel experimental approach to study in situ the regional, multiaxial mechanical behavior of both normal and diabetic human anterior lens capsules. Furthermore, we use these data to calculate material parameters in a nonlinear stress-strain relation via a custom sub-domain inverse finite element method (FEM). These parameters are then used to predict capsular stresses in response to imposed loads using a forward FEM model. Our results for both normal and diabetic human eyes show that the anterior lens capsule exhibits a nonlinear pseudoelastic behavior over finite strains that is typical of soft tissues, and that strains are principal relative to meridional and circumferential directions. Experimental data and parameter estimation suggest further that the capsule is regionally anisotropic, with the circumferential direction becoming increasingly stiffer than the meridional direction towards the equator. Although both normal and diabetic lens capsules exhibited these general characteristic behaviors, diabetic capsules were significantly stiffer at each distension. Finally, the forward FEM model predicted a nearly uniform, equibiaxial stress field during normalcy that will be perturbed by cataract surgery. Such mechanical perturbations may be an underlying modulator of the sustained errant epithelial cell behavior that is observed well after cataract surgery and may ultimately contribute to opacification of the posterior lens capsule.
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Affiliation(s)
- R M Pedrigi
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
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21
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Abolmaali A, Schachar RA, Le T. Sensitivity study of human crystalline lens accommodation. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2007; 85:77-90. [PMID: 17005291 DOI: 10.1016/j.cmpb.2006.08.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2006] [Revised: 08/22/2006] [Accepted: 08/24/2006] [Indexed: 05/12/2023]
Abstract
A nonlinear axisymmetric finite element method (FEM) analysis was employed to determine the critical geometric and material properties that affect human accommodation. In this model, commencing at zero, zonular traction on all lens profiles resulted in central lenticular surface steepening and peripheral surface flattening, with a simultaneous increase in central lens thickness and central optical power. An age-related decline in maximum zonular tension appears to be the most likely etiology for the decrease in accommodative amplitude with age.
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Affiliation(s)
- A Abolmaali
- Department of Civil and Environmental Engineering, University of Texas at Arlington, TX 76019, USA
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22
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Schachar RA, Abolmaali A, Le T. Insights into the age-related decline in the amplitude of accommodation of the human lens using a non-linear finite-element model. Br J Ophthalmol 2006; 90:1304-9. [PMID: 16854823 PMCID: PMC1857424 DOI: 10.1136/bjo.2006.100347] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/05/2006] [Indexed: 11/04/2022]
Abstract
AIM To understand the effect of the geometric and material properties of the lens on the age-related decline in accommodative amplitude. METHODS Using a non-linear finite-element model, a parametric assessment was carried out to determine the effect of stiffness of the cortex, nucleus, capsule and zonules, and that of thickness of the capsule and lens, on the change in central optical power (COP) associated with zonular traction. Convergence was required for all solutions. RESULTS Increasing either capsular stiffness or capsular thickness was associated with an increase in the change in COP for any specific amount of zonular traction. Weakening the attachment between the capsule and its underlying cortex increased the magnitude of the change in COP. When the hardness of the total lens stroma, cortex or nucleus was increased, there was a reduction in the amount of change in COP associated with a fixed amount of zonular traction. CONCLUSIONS Increasing lens hardness reduces accommodative amplitude; however, as hardness of the lens does not occur until after the fourth decade of life, the age-related decline in accommodative amplitude must be due to another mechanism. One explanation is a progressive decline in the magnitude of the maximum force exerted by the zonules with ageing.
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MESH Headings
- Accommodation, Ocular/physiology
- Adult
- Aging/pathology
- Aging/physiology
- Elasticity
- Finite Element Analysis
- Humans
- Lens Capsule, Crystalline/anatomy & histology
- Lens Capsule, Crystalline/physiology
- Lens Cortex, Crystalline/anatomy & histology
- Lens Cortex, Crystalline/physiology
- Lens Nucleus, Crystalline/anatomy & histology
- Lens Nucleus, Crystalline/physiology
- Lens, Crystalline/anatomy & histology
- Lens, Crystalline/physiology
- Middle Aged
- Models, Biological
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Affiliation(s)
- R A Schachar
- Department of Physics, University of Texas at Arlington, Arlington, TX, USA.
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23
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Schachar RA, Kamangar F. Computer image analysis of ultrasound biomicroscopy of primate accommodation. Eye (Lond) 2006; 20:226-33. [PMID: 15818391 DOI: 10.1038/sj.eye.6701838] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
PURPOSE To assess and correct images of the eye for movements that can confound the evaluation of the presence, direction, and magnitude of intraocular movement of the crystalline lens equator during centrally induced ciliary muscle contraction (accommodation). METHOD Ultrasound biomicroscopic (UBM) video images of a cynomologus monkey crystalline lens were obtained from an independent source. The images, prior to, during, and following electrical stimulation of the Edinger-Westphal (EW) nucleus were compared for evidence of movement of the crystalline lens equator. Extraocular eye movements were assessed by use of objective computer imaging analysis techniques. RESULTS Extraocular eye movements were identified and reduced by using objective computer imaging analysis techniques to register and realign the corneal images. Highly significant corrections are required to effect corneal realignment. Analysis of paired and registered images from this data source indicates that any movements of the primate lens equator are not detectable when maximum accommodation was induced by EW stimulation. CONCLUSION The displacement of the edge of the primate crystalline lens equator during electrically induced contraction of the ciliary muscle is a small displacement phenomenon, only analysable after confounding extraocular movements are removed from the compared images.
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Affiliation(s)
- R A Schachar
- Department of Physics, University of Texas at Arlington, Arlington, TX, USA.
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24
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Chien CHM, Huang T, Schachar RA. Analysis of human crystalline lens accommodation. J Biomech 2006; 39:672-80. [PMID: 16023655 DOI: 10.1016/j.jbiomech.2005.01.017] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2004] [Accepted: 01/10/2005] [Indexed: 11/18/2022]
Abstract
The behavior of the human crystalline lens during accommodation is analytically studied. The lens is modeled as a closed axisymmetrical membrane shell of varying thickness enclosing an incompressible liquid. To simulate zonular tension associated with lenticular accommodation, an axisymmetrical radial force or displacement is imposed around the shell equator. Two second-order, simultaneous, nonlinear governing differential equations are derived. Numerical results, obtained from the investigation of human lens profiles of three independently published MRI images and a drawing of a microphotograph, demonstrate that when zonular traction within the physiological force range of the ciliary muscle is exerted, both central lens thickness and central optical power increase. Qualitatively, these increases are independent of lens shape. However, the magnitude of these changes is dependent on the initial profile of the lens and is enhanced by the "natural" variation in capsular thickness. Only when a pulling force significantly exceeds the force capacity of the ciliary muscle does the lens flatten and its central thickness and optical power decrease.
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Affiliation(s)
- Chang-Hai M Chien
- Department of Civil and Environmental Engineering, University of Texas at Arlington, Arlington, TX 76019, USA
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25
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Hermans EA, Dubbelman M, van der Heijde GL, Heethaar RM. Estimating the external force acting on the human eye lens during accommodation by finite element modelling. Vision Res 2006; 46:3642-50. [PMID: 16750240 DOI: 10.1016/j.visres.2006.04.012] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2006] [Revised: 03/31/2006] [Accepted: 04/17/2006] [Indexed: 11/20/2022]
Abstract
Using new geometric information on the shape of the lens that has recently become available, a finite element model has been developed in order to estimate the forces that act on the lens during accommodation for a typical 29-year-old human eye. To investigate the influence of the anterior, posterior and central zonular fibres insertion regions, three models with different configurations were built. All three configurations appeared to be capable of inducing the required accommodative changes in the lens. Based on material properties from the literature, the estimated summed net force for each of the three models was approximately 0.08 N.
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Affiliation(s)
- E A Hermans
- Department of Physics and Medical Technology, VU University Medical Centre, Amsterdam, The Netherlands.
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26
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Glasser A, Wendt M, Ostrin L. Accommodative changes in lens diameter in rhesus monkeys. Invest Ophthalmol Vis Sci 2006; 47:278-86. [PMID: 16384974 PMCID: PMC2915931 DOI: 10.1167/iovs.05-0890] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Some debate surrounds the accommodative mechanism in primates, particularly whether the lens equatorial diameter increases or decreases during accommodation. This study has been undertaken to measure the relationship between changes in lens diameter and refraction during accommodation in rhesus monkeys. METHODS Photorefraction was used to measure accommodation, and goniovideography was used to measure accommodative changes in lens diameter in the iridectomized eyes of two rhesus monkeys. Accommodation was stimulated through the full amplitude available to each eye by stimulation of the Edinger-Westphal nucleus of the brain. Dynamic measurement of refractive changes followed by dynamic measurements of changes in lens diameter for the same stimulus current amplitudes allow the relationship between refraction and lens diameter to be determined. RESULTS Lens diameter decreased relatively linearly during accommodation by 0.055 mm/diopter (D), resulting in an overall decrease in lens diameter of approximately 7% of the unaccommodated lens diameter for approximately 12 D of accommodation. CONCLUSIONS The rhesus monkey lens diameter decreases systematically with the refractive change during accommodation in accordance with the Helmholtz accommodative mechanism and in contrast to the accommodative mechanism originally proposed by Tscherning.
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Affiliation(s)
- Adrian Glasser
- College of Optometry, University of Houston, Houston, Texas 77204-2020, USA.
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27
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Schachar RA. Central surface curvatures of postmortem- extracted intact human crystalline lenses: implications for understanding the mechanism of accommodation. Ophthalmology 2004; 111:1699-704. [PMID: 15350325 DOI: 10.1016/j.ophtha.2004.03.033] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2004] [Accepted: 03/05/2004] [Indexed: 11/16/2022] Open
Abstract
PURPOSE To measure the radii of curvature of postmortem, whole, encapsulated human crystalline lenses, free of all zonular attachments, and to calculate their corresponding optical powers. DESIGN Experimental study. PARTICIPANTS Thirty human crystalline lenses from donors with a mean age of 33.6+/-14.4 years. METHODS Intact clear human crystalline lenses were obtained within an average of 21 hours of death. The lenses were removed from the eye by the contributing eye bank and shipped in Optisol-GS, a physiologic preservative storage medium. These lenses, with intact capsules, were freed of all zonular attachments. The lenses were stored at 7 degrees C and were maintained in the same storage medium during the period that they were held for evaluation. Using a portable Keratron Scout corneal topographer (Eyequip, Ponte Vedra Beach, FL) fixed to an optical bench, the radii of curvatures of the anterior and posterior surfaces of the crystalline lens were measured daily for 10 days after receipt of the tissue. The capsules of the crystalline lenses remained intact, and the lenses were clear throughout the study. Measurements were made at room temperature after removing the lens from storage. Eight repetitions of the topography were made from each surface on each day to determine the accuracy and stability of the measurement. Profile photographs were taken daily to establish the central crystalline lens thickness. The corresponding optical power of each physiologically maintained crystalline lens was calculated. MAIN OUTCOME MEASURES The main outcome measures were the central anterior radius of curvature, the central posterior radius of curvature, the central thickness of each crystalline lens, and the amount of change in these parameters over 10 days. RESULTS The means +/- standard deviations of the central anterior and posterior radii of curvatures of the 30 adult lenses were 10.5+/-0.6 mm and 7.1+/-1.0 mm, respectively. The mean +/- standard deviation of the central thickness, as measured from profile photographs, was 3.9+/-0.5 mm. These mean measurements remained stable for up to 5 days after receipt of the tissue. The mean and standard deviation of the calculated optical power of these postmortem, physiologically maintained, intact human crystalline lenses from donors with a mean age of 33.6 years was 19.8+/-1.7 diopters. CONCLUSIONS Lenses free of zonular tension are at an optical power that would be associated with optimal distance acuity.
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29
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Chien CHM, Huang T, Schachar RA. A mathematical expression for the human crystalline lens. ACTA ACUST UNITED AC 2003. [DOI: 10.1007/s12019-003-0028-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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30
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Schachar RA, Lewis FL. Error tolerance in Helmholtzian Accommodation. Ophthalmology 2003; 110:2066-7; author reply 2067. [PMID: 14522798 DOI: 10.1016/s0161-6420(03)00910-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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31
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Lee DB. Error tolerance in helmholtzian accommodation: Author reply. Ophthalmology 2003. [DOI: 10.1016/s0161-6420(03)00911-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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Schachar RA. Regarding the surgical reversal of presbyopia (SRP) surgery for presbyopia, vol 108, number 12, December 2001, 2161-2. Ophthalmology 2003; 110:872-3; author reply 873. [PMID: 12750072 DOI: 10.1016/s0161-6420(02)01854-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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33
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Marmer RH. Presbyopia, accommodation, and mature catenary. Ophthalmology 2002; 109:1415; author reply 1416-8. [PMID: 12153785 DOI: 10.1016/s0161-6420(02)01137-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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