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Cheng C. Tissue, cellular, and molecular level determinants for eye lens stiffness and elasticity. FRONTIERS IN OPHTHALMOLOGY 2024; 4:1456474. [PMID: 39176256 PMCID: PMC11339033 DOI: 10.3389/fopht.2024.1456474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/28/2024] [Accepted: 07/26/2024] [Indexed: 08/24/2024]
Abstract
The eye lens is a transparent, ellipsoid tissue in the anterior chamber that is required for the fine focusing of light onto the retina to transmit a clear image. The focusing function of the lens is tied to tissue transparency, refractive index, and biomechanical properties. The stiffness and elasticity or resilience of the human lens allows for shape changes during accommodation to focus light from objects near and far. It has long been hypothesized that changes in lens biomechanical properties with age lead to the loss of accommodative ability and the need for reading glasses with age. However, the cellular and molecular mechanisms that influence lens biomechanical properties and/or change with age remain unclear. Studies of lens stiffness and resilience in mouse models with genetic defects or at advanced age inform us of the cytoskeletal, structural, and morphometric parameters that are important for biomechanical stability. In this review, we will explore whether: 1) tissue level changes, including the capsule, lens volume, and nucleus volume, 2) cellular level alterations, including cell packing, suture organization, and complex membrane interdigitations, and 3) molecular scale modifications, including the F-actin and intermediate filament networks, protein modifications, lipids in the cell membrane, and hydrostatic pressure, influence overall lens biomechanical properties.
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Affiliation(s)
- Catherine Cheng
- School of Optometry and Vision Science Program, Indiana University, Bloomington, IN, United States
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2
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Donaldson PJ, Petrova RS, Nair N, Chen Y, Schey KL. Regulation of water flow in the ocular lens: new roles for aquaporins. J Physiol 2024; 602:3041-3056. [PMID: 37843390 PMCID: PMC11018719 DOI: 10.1113/jp284102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 09/28/2023] [Indexed: 10/17/2023] Open
Abstract
The ocular lens is an important determinant of overall vision quality whose refractive and transparent properties change throughout life. The lens operates an internal microcirculation system that generates circulating fluxes of ions, water and nutrients that maintain the transparency and refractive properties of the lens. This flow of water generates a substantial hydrostatic pressure gradient which is regulated by a dual feedback system that uses the mechanosensitive channels TRPV1 and TRPV4 to sense decreases and increases, respectively, in the pressure gradient. This regulation of water flow (pressure) and hence overall lens water content, sets the two key parameters, lens geometry and the gradient of refractive index, which determine the refractive properties of the lens. Here we focus on the roles played by the aquaporin family of water channels in mediating lens water fluxes, with a specific focus on AQP5 as a regulated water channel in the lens. We show that in addition to regulating the activity of ion transporters, which generate local osmotic gradients that drive lens water flow, the TRPV1/4-mediated dual feedback system also modulates the membrane trafficking of AQP5 in the anterior influx pathway and equatorial efflux zone of the lens. Since both lens pressure and AQP5-mediated water permeability (P H 2 O ${P_{{{\mathrm{H}}_{\mathrm{2}}}{\mathrm{O}}}}$ ) can be altered by changes in the tension applied to the lens surface via modulating ciliary muscle contraction we propose extrinsic modulation of lens water flow as a potential mechanism to alter the refractive properties of the lens to ensure light remains focused on the retina throughout life.
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Affiliation(s)
- Paul J. Donaldson
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Rosica S. Petrova
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Nikhil Nair
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Yadi Chen
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, University of Auckland, Auckland, New Zealand
| | - Kevin L. Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN, USA
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Petrova RS, Nair N, Bavana N, Chen Y, Schey KL, Donaldson PJ. Modulation of Membrane Trafficking of AQP5 in the Lens in Response to Changes in Zonular Tension Is Mediated by the Mechanosensitive Channel TRPV1. Int J Mol Sci 2023; 24:9080. [PMID: 37240426 PMCID: PMC10219244 DOI: 10.3390/ijms24109080] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 05/16/2023] [Accepted: 05/18/2023] [Indexed: 05/28/2023] Open
Abstract
In mice, the contraction of the ciliary muscle via the administration of pilocarpine reduces the zonular tension applied to the lens and activates the TRPV1-mediated arm of a dual feedback system that regulates the lens' hydrostatic pressure gradient. In the rat lens, this pilocarpine-induced reduction in zonular tension also causes the water channel AQP5 to be removed from the membranes of fiber cells located in the anterior influx and equatorial efflux zones. Here, we determined whether this pilocarpine-induced membrane trafficking of AQP5 is also regulated by the activation of TRPV1. Using microelectrode-based methods to measure surface pressure, we found that pilocarpine also increased pressure in the rat lenses via the activation of TRPV1, while pilocarpine-induced removal of AQP5 from the membrane observed using immunolabelling was abolished by pre-incubation of the lenses with a TRPV1 inhibitor. In contrast, mimicking the actions of pilocarpine by blocking TRPV4 and then activating TRPV1 resulted in sustained increase in pressure and the removal of AQP5 from the anterior influx and equatorial efflux zones. These results show that the removal of AQP5 in response to a decrease in zonular tension is mediated by TRPV1 and suggest that regional changes to PH2O contribute to lens hydrostatic pressure gradient regulation.
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Affiliation(s)
- Rosica S. Petrova
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, Faculty of Medical and Health Sciences, The University of Auckland, Auckland 1023, New Zealand
| | - Nikhil Nair
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, Faculty of Medical and Health Sciences, The University of Auckland, Auckland 1023, New Zealand
| | - Nandini Bavana
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, Faculty of Medical and Health Sciences, The University of Auckland, Auckland 1023, New Zealand
| | - Yadi Chen
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, Faculty of Medical and Health Sciences, The University of Auckland, Auckland 1023, New Zealand
| | - Kevin L. Schey
- Department of Biochemistry, Mass Spectrometry Research Center, Vanderbilt University, Nashville, TN 37232, USA
| | - Paul J. Donaldson
- Department of Physiology, School of Medical Sciences, New Zealand National Eye Center, Faculty of Medical and Health Sciences, The University of Auckland, Auckland 1023, New Zealand
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Design of an Automatically Controlled Multi-Axis Stretching Device for Mechanical Evaluations of the Anterior Eye Segment. Bioengineering (Basel) 2023; 10:bioengineering10020142. [PMID: 36829636 PMCID: PMC9952546 DOI: 10.3390/bioengineering10020142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Revised: 01/14/2023] [Accepted: 01/18/2023] [Indexed: 01/22/2023] Open
Abstract
The young eye has an accommodative ability involving lens shape changes to focus over different distances. This function gradually decreases with age, resulting in presbyopia. Greater insights into the mechanical properties of anterior eye structures can improve understanding of the causes of presbyopia. The present study aims to develop a multi-axis stretching device for evaluating the mechanical properties of the intact eye lens. A stretching device integrating the mechanical stretcher, motor, torque sensor and data transmission mechanism was designed and developed by 3D printing. The mechanical stretcher can convert rotation into radial movement, both at constant speeds, according to the spiral of Archimedes. The loading unit equipped with eight jaws can hold the eye sample tightly. The developed device was validated with a spring of known constant and was further tested with anterior porcine eye segments. The validation experiment using the spring resulted in stiffness values close to the theoretical spring constant. Findings from measurements with porcine eye samples indicated that the measured forces are within the ranges reported in the literature. The developed multi-axis stretching device has good repeatability during experiments with similar settings and can be reliably used for mechanical evaluations of the intact eye lens.
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Cheng C, Wang K, Hoshino M, Uesugi K, Yagi N, Pierscionek B. EphA2 Affects Development of the Eye Lens Nucleus and the Gradient of Refractive Index. Invest Ophthalmol Vis Sci 2022; 63:2. [PMID: 34978559 PMCID: PMC8742528 DOI: 10.1167/iovs.63.1.2] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Purpose Our studies in mouse eye lenses demonstrate that ephrin-A5 and EphA2 are needed for normal epithelial cells and lens transparency. We sought to determine whether EphA2 and ephrin-A5 are important for lens morphometrics, nucleus formation, and refractive index. Methods We performed tissue morphometric measurements, electron microscopy, Western blots, and interferometric measurements using an X-ray synchrotron beam source to measure the gradient of refractive index (GRIN) to compare mouse lenses with genetic disruption of EphA2 or ephrin-A5. Results Morphometric analysis revealed that although there is no change in the overall lens volume, there is a change in lens shape in both EphA2-/- lenses and ephrin-A5-/- lenses. Surprisingly, EphA2-/- lenses had small and soft lens nuclei different from hard lens nuclei of control lenses. SEM images revealed changes in cell morphology of EphA2-/- fiber cells close to the center of the lens. Inner EphA2-/- lens fibers had more pronounced tongue-and-groove interdigitations and formed globular membrane morphology only in the deepest layers of the lens nucleus. We did not observe nuclear defects in ephrin-A5-/- lenses. There was an overall decrease in magnitude of refractive index across EphA2-/- lenses, which is most pronounced in the nucleus. Conclusions This work reveals that Eph-ephrin signaling plays a role in fiber cell maturation, nuclear compaction, and lens shape. Loss of EphA2 disrupts the nuclear compaction resulting in a small lens nucleus. Our data suggest that Eph-ephrin signaling may be required for fiber cell membrane reorganization and compaction and for establishing a normal GRIN.
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Affiliation(s)
- Catherine Cheng
- School of Optometry, Indiana University, Bloomington, IN, United States
| | - Kehao Wang
- Beijing Advanced Innovation Centre for Biomedical Engineering, Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Engineering Medicine, Beihang University, Beijing, China
| | - Masato Hoshino
- Japan Synchrotron Radiation Research Institute (Spring-8), 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 Japan
| | - Kentaro Uesugi
- Japan Synchrotron Radiation Research Institute (Spring-8), 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 Japan
| | - Naoto Yagi
- Japan Synchrotron Radiation Research Institute (Spring-8), 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 Japan
| | - Barbara Pierscionek
- Faculty of Health, Education, Medicine and Social Care, Medical Technology Research Centre, Anglia Ruskin University, Chelmsford Campus, United Kingdom
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Cheng C. EphA2 and Ephrin-A5 Guide Eye Lens Suture Alignment and Influence Whole Lens Resilience. Invest Ophthalmol Vis Sci 2021; 62:3. [PMID: 34854885 PMCID: PMC8648058 DOI: 10.1167/iovs.62.15.3] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose Fine focusing of light by the eye lens onto the retina relies on the ability of the lens to change shape during the process of accommodation. Little is known about the cellular structures that regulate elasticity and resilience. We tested whether Eph–ephrin signaling is involved in lens biomechanical properties. Methods We used confocal microscopy and tissue mechanical testing to examine mouse lenses with genetic disruption of EphA2 or ephrin-A5. Results Confocal imaging revealed misalignment of the suture between each shell of newly added fiber cells in knockout lenses. Despite having disordered sutures, loss of EphA2 or ephrin-A5 did not affect lens stiffness. Surprisingly, knockout lenses were more resilient and recovered almost completely after load removal. Confocal microscopy and quantitative image analysis from live lenses before, during, and after compression revealed that knockout lenses had misaligned Y-sutures, leading to a change in force distribution during compression. Knockout lenses displayed decreased separation of fiber cell tips at the anterior suture at high loads and had more complete recovery after load removal, which leads to improved whole-lens resiliency. Conclusions EphA2 and ephrin-A5 are needed for normal patterning of fiber cell tips and the formation of a well-aligned Y-suture with fiber tips stacked on top of previous generations of fiber cells. The misalignment of lens sutures leads to increased resilience after compression. The data suggest that alignment of the Y-suture may constrain the overall elasticity and resilience of the lens.
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Affiliation(s)
- Catherine Cheng
- School of Optometry and Vision Science Program, Indiana University, Bloomington, Indiana, United States
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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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Wei H, Wolffsohn JS, Gomes de Oliveira O, Davies LN. An Artificial Lens Capsule with a Lens Radial Stretching System Mimicking Dynamic Eye Focusing. Polymers (Basel) 2021; 13:polym13203552. [PMID: 34685312 PMCID: PMC8540979 DOI: 10.3390/polym13203552] [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: 10/08/2021] [Accepted: 10/09/2021] [Indexed: 11/17/2022] Open
Abstract
Presbyopia is a common eye disorder among aged people which is attributed to the loss of accommodation of the crystalline lens due to the increasing stiffness. One of the potential techniques to correct presbyopia involves removing the lens substance inside the capsule and replacing it with an artificial lens. The development of such devices, e.g., accommodating intraocular lenses (AIOLs), relies on the understanding of the biomechanical behaviour of the lens capsule and the essential design verification ex vivo. To mimic the eye’s dynamic focusing ability (accommodation), an artificial lens capsule (ALC), from silicone rubber accompanied by a lens radial stretching system (LRSS) was developed. The ALC was manufactured to offer a dimension and deforming behaviour replicating the human lens capsule. The LRSS was calibrated to provide a radial stretch simulating the change of diameter of capsules during accommodating process. The biomechanical function of the ALC was addressed by studying its evolution behaviour and reaction force under multiaxial stretch from the LRSS. The study highlighted the convenience of this application by performing preliminary tests on prototypes of ophthalmic devices (e.g., AIOLs) to restore accommodation.
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Affiliation(s)
- Huidong Wei
- College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK;
- Rayner Intraocular Lenses Limited, Worthing BN14 8AQ, UK;
- Correspondence: (H.W.); (J.S.W.); Tel.: +44-(0)121-204-4140 (J.S.W.)
| | - James S. Wolffsohn
- College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK;
- Correspondence: (H.W.); (J.S.W.); Tel.: +44-(0)121-204-4140 (J.S.W.)
| | | | - Leon N. Davies
- College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK;
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Korenfeld MS, Robertson SM, Stein JM, Evans DG, Rauchman SH, Sall KN, Venkataraman S, Chen BL, Wuttke M, Burns W. Topical lipoic acid choline ester eye drop for improvement of near visual acuity in subjects with presbyopia: a safety and preliminary efficacy trial. Eye (Lond) 2021; 35:3292-3301. [PMID: 33514891 PMCID: PMC8602643 DOI: 10.1038/s41433-020-01391-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 11/15/2020] [Accepted: 12/18/2020] [Indexed: 11/30/2022] Open
Abstract
Objectives This study evaluated the safety of topical lipoic acid choline ester (UNR844, 1.5%) ophthalmic solution and its efficacy in improving distance-corrected near visual acuity (DCNVA) in subjects with presbyopia. Subjects and methods This was a prospective, randomized, double-masked, and multicentre clinical trial. Subjects with a diagnosis of presbyopia (n = 75) were randomized 2:1 to UNR844 or placebo. On days 1–7, all subjects were dosed unilaterally (twice a day, b.i.d.) in their non-dominant eye to ensure safety and tolerability prior to days 8–91 when dosing was changed to bilateral (b.i.d.). Clinical assessments, including DCNVA and adverse events (AEs), were recorded at each study visit. Patients who completed the study were recruited into a non-interventional follow-up study that monitored them until 7 months after their final UNR844 exposure. The primary endpoints were safety and the mean change in DCNVA from baseline in the study eye. Results UNR844 administration (n = 50) produced no safety concerns and was well-tolerated, with no clinically-relevant changes in best-corrected distance visual acuity, pupil size, intraocular pressure, or discontinuations due to adverse events. DCNVA improved in the study eye in the UNR844 group compared to placebo during the 91 days of treatment [UNR844 vs. placebo, mean change in LogMAR (SD); −0.159 (0.120) vs. −0.079 (0.116)]. Bilateral DCNVA improved, with 53.1% UNR844 vs. 21.7% placebo subjects gaining ≥10 letters. Improvements in DCNVA were sustained at 5 and 7 months after UNR844 dosing ceased. Conclusions These results support further development of UNR844 ophthalmic solution for the treatment of presbyopia.
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Affiliation(s)
- Michael S Korenfeld
- Comprehensive Eye Care Center Ltd, 901 East Third Street, Washington, MO, 63090, USA.
| | - Stella M Robertson
- Arrochar Consulting, LLC, 7045 Shadow Creek Court, Fort Worth, TX, 76132, USA
| | - Jerry M Stein
- Summer Creek Consulting, LLC, 8101 Rain Dance Trail, Fort Worth, TX, 76123, USA
| | - David G Evans
- Total Eye Care, PA, 6060 Primacy Parkway, Memphis, TN, 38119, USA
| | - Steven H Rauchman
- North Valley Eye Medical Group, 11550 Indian Hills Road, Mission Hill, CA, 91345, USA
| | - Kenneth N Sall
- Sall Research Medical Centre, 11423 87th Street, Artesia, CA, 90701, USA
| | - Subha Venkataraman
- Novartis Pharmaceutical Corporation, 1 Health Plaza, East Hanover, NJ, 07936, USA
| | - Bee-Lian Chen
- Novartis Pharmaceutical Corporation, 1 Health Plaza, East Hanover, NJ, 07936, USA
| | | | - William Burns
- Encore Vision, Inc., 1120 South Freeway, Suite 118, Fort Worth, TX, 76104, USA
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Nagashima H, Sasaki N, Amano S, Nakamura S, Hayano M, Tsubota K. Oral administration of resveratrol or lactic acid bacterium improves lens elasticity. Sci Rep 2021; 11:2174. [PMID: 33500490 PMCID: PMC7838312 DOI: 10.1038/s41598-021-81748-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 01/08/2021] [Indexed: 02/03/2023] Open
Abstract
A decrease in the elasticity of the ocular lens during aging is associated with loss of the accommodative ability of the eye, leading to presbyopia. Although near vision impairment is a social issue affecting the length of healthy life expectancy and productivity of elderly people, an effective treatment to improve near vision has not yet become available. Here we examined the effect of Enterococcus faecium WB2000, Lactobacillus pentosus TJ515, and resveratrol on lens elasticity in rats, where the stiffness of the ocular lens increases exponentially during the aging process. A combination of WB2000 and resveratrol improved lens elasticity not only in the long term but also with just short-term treatment. In addition, TJ515 decreased stiffness in the eye lens with long-term treatment. Therefore, the oral administration of WB2000 and resveratrol or TJ515 may be a potential approach for managing the progression of near vision impairment.
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Affiliation(s)
- Hayato Nagashima
- Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan
- Department of Plastic and Reconstructive Surgery, Keio University School of Medicine, Tokyo, Japan
| | - Nobunari Sasaki
- Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan
- Tsubota Laboratory, Inc., Tokyo, Japan
| | - Sachie Amano
- Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan
| | - Shigeru Nakamura
- Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan
| | - Motoshi Hayano
- Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan
- Tsubota Laboratory, Inc., Tokyo, Japan
| | - Kazuo Tsubota
- Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan.
- Tsubota Laboratory, Inc., Tokyo, Japan.
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Cheng C, Parreno J, Nowak RB, Biswas SK, Wang K, Hoshino M, Uesugi K, Yagi N, Moncaster JA, Lo WK, Pierscionek B, Fowler VM. Age-related changes in eye lens biomechanics, morphology, refractive index and transparency. Aging (Albany NY) 2019; 11:12497-12531. [PMID: 31844034 PMCID: PMC6949082 DOI: 10.18632/aging.102584] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 11/26/2019] [Indexed: 04/09/2023]
Abstract
Life-long eye lens function requires an appropriate gradient refractive index, biomechanical integrity and transparency. We conducted an extensive study of wild-type mouse lenses 1-30 months of age to define common age-related changes. Biomechanical testing and morphometrics revealed an increase in lens volume and stiffness with age. Lens capsule thickness and peripheral fiber cell widths increased between 2 to 4 months of age but not further, and thus, cannot account for significant age-dependent increases in lens stiffness after 4 months. In lenses from mice older than 12 months, we routinely observed cataracts due to changes in cell structure, with anterior cataracts due to incomplete suture closure and a cortical ring cataract corresponding to a zone of compaction in cortical lens fiber cells. Refractive index measurements showed a rapid growth in peak refractive index between 1 to 6 months of age, and the area of highest refractive index is correlated with increases in lens nucleus size with age. These data provide a comprehensive overview of age-related changes in murine lenses, including lens size, stiffness, nuclear fraction, refractive index, transparency, capsule thickness and cell structure. Our results suggest similarities between murine and primate lenses and provide a baseline for future lens aging studies.
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Affiliation(s)
- Catherine Cheng
- School of Optometry, Indiana University, Bloomington, IN 47405, USA
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Justin Parreno
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Roberta B. Nowak
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Sondip K. Biswas
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA 30303, USA
| | - Kehao Wang
- School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom
| | - Masato Hoshino
- Japan Synchrotron Radiation Research Institute (Spring-8), Sayo-cho, Sayo-gun, Hyogo, Japan
| | - Kentaro Uesugi
- Japan Synchrotron Radiation Research Institute (Spring-8), Sayo-cho, Sayo-gun, Hyogo, Japan
| | - Naoto Yagi
- Japan Synchrotron Radiation Research Institute (Spring-8), Sayo-cho, Sayo-gun, Hyogo, Japan
| | - Juliet A. Moncaster
- Department of Radiology, Boston University School of Medicine, Boston, MA 02118, USA
| | - Woo-Kuen Lo
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA 30303, USA
| | - Barbara Pierscionek
- School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom
| | - Velia M. Fowler
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
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12
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Parreno J, Cheng C, Nowak RB, Fowler VM. The effects of mechanical strain on mouse eye lens capsule and cellular microstructure. Mol Biol Cell 2018; 29:1963-1974. [PMID: 30088796 PMCID: PMC6232967 DOI: 10.1091/mbc.e18-01-0035] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The mouse eye lens was used as a model for multiscale transfer of loads. In the lens, compressive strain is distributed across specific lens tissue microstructures, including the extracellular capsule, as well as the epithelial and fiber cells. The removal of high loads resulted in complete recovery of most, but not all, microstructures. The understanding of multiscale load transfer within complex soft tissues is incomplete. The eye lens is ideal for multiscale mechanical studies because its principal function is to fine-focus light at different distances onto the retina via shape changes. The biomechanical function, resiliency, and intricate microstructure of the lens makes it an excellent nonconnective soft tissue model. We hypothesized that strain applied onto whole-lens tissue leads to deformation of specific microstructures and that this deformation is reversible following load removal. For this examination, mouse lenses were compressed by sequential application of increasing load. Using confocal microscopy and quantitative image analysis, we determined that axial strain ≥10% reduces capsule thickness, expands epithelial cell area, and separates fiber cell tips at the anterior region. At the equatorial region, strain ≥6% increases fiber cell widths. The effects of strain on lens epithelial cell area, capsule thickness, and fiber cell widths are reversible following the release from strain. However, the separation of fiber cell tips is irreversible at high loads. This irreversible separation between fiber cell tips leads to incomplete whole-lens resiliency. The lens is an accessible biomechanical model system that provides new insights on multiscale transfer of loads in soft tissues.
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Affiliation(s)
- Justin Parreno
- Department of Molecular Medicine, Scripps Research Institute, La Jolla, CA 92037
| | - Catherine Cheng
- Department of Molecular Medicine, Scripps Research Institute, La Jolla, CA 92037
| | - Roberta B Nowak
- Department of Molecular Medicine, Scripps Research Institute, La Jolla, CA 92037
| | - Velia M Fowler
- Department of Molecular Medicine, Scripps Research Institute, La Jolla, CA 92037
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Webb JN, Dong C, Bernal A, Scarcelli G. Simulating the Mechanics of Lens Accommodation via a Manual Lens Stretcher. J Vis Exp 2018. [PMID: 29553512 DOI: 10.3791/57162] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The goal of this protocol is to mimic the biomechanics of physiological accommodation in a cost-efficient, practical manner. Accommodation is achieved through the contraction of the ciliary body and relaxation of zonule fibers, which results in the thickening of the lens necessary for near vision. Here, we present a novel, simple method in which accommodation is replicated by tensing the zonules connected to the lens capsule via a manual lens stretcher (MLS). This method monitors the radial stretching achieved by a lens when subjected to a consistent force and allows for a comparison of accommodating lenses, which can be stretched, to non-accommodating lenses, which cannot be stretched. Importantly, the stretcher couples to the zonules directly, and not to the sclera of the eye, thus only requiring the lens, zonules, and ciliary body rather than the entire globe sample. This difference can significantly decrease the cost of acquiring donor cadaver lenses by about 62% compared to acquiring an entire globe.
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Affiliation(s)
- Joshua N Webb
- Fischell Department of Bioengineering, University of Maryland
| | - Caroline Dong
- Fischell Department of Bioengineering, University of Maryland
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14
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Anterior lens capsule strains during simulated accommodation in porcine eyes. Exp Eye Res 2017; 168:19-27. [PMID: 29288023 DOI: 10.1016/j.exer.2017.12.008] [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: 08/23/2017] [Revised: 12/02/2017] [Accepted: 12/22/2017] [Indexed: 11/20/2022]
Abstract
Experimental protocols have been developed to measure the spatial variation of the mechanical strains induced in the lens capsule during ex vivo lens stretching. The paper describes the application of these protocols to porcine lenses. The deformations and mechanical strains developed in the anterior capsule during each experiment were determined using full field digital image correlation techniques, by means of a speckle pattern applied to the lens surface. Several speckling techniques and illumination methods were assessed before a suitable combination was found. Additional data on the cross section shape of the anterior lens surface were obtained by Scheimpflug photography, to provide a means of correcting for lens curvature effects in the determination of the strains developed in the plane of the capsule. The capsule strains in porcine lenses exhibit non-linear behaviour, and hysteresis during loading and unloading. Peripheral regions experience higher magnitude strains than regions near the lens pole. The paper demonstrates the successful application of a procedure to make direct measurements of capsule strains simultaneously with ex vivo radial lens stretching. This experimental technique is applicable to future investigations on the mechanical characteristics of human lenses.
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15
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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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16
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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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17
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Cheng C, Gokhin DS, Nowak RB, Fowler VM. Sequential Application of Glass Coverslips to Assess the Compressive Stiffness of the Mouse Lens: Strain and Morphometric Analyses. J Vis Exp 2016. [PMID: 27166880 DOI: 10.3791/53986] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The eye lens is a transparent organ that refracts and focuses light to form a clear image on the retina. In humans, ciliary muscles contract to deform the lens, leading to an increase in the lens' optical power to focus on nearby objects, a process known as accommodation. Age-related changes in lens stiffness have been linked to presbyopia, a reduction in the lens' ability to accommodate, and, by extension, the need for reading glasses. Even though mouse lenses do not accommodate or develop presbyopia, mouse models can provide an invaluable genetic tool for understanding lens pathologies, and the accelerated aging observed in mice enables the study of age-related changes in the lens. This protocol demonstrates a simple, precise, and cost-effective method for determining mouse lens stiffness, using glass coverslips to apply sequentially increasing compressive loads onto the lens. Representative data confirm that mouse lenses become stiffer with age, like human lenses. This method is highly reproducible and can potentially be scaled up to mechanically test lenses from larger animals.
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Affiliation(s)
- Catherine Cheng
- Department of Cell and Molecular Biology, The Scripps Research Institute
| | - David S Gokhin
- Department of Cell and Molecular Biology, The Scripps Research Institute
| | - Roberta B Nowak
- Department of Cell and Molecular Biology, The Scripps Research Institute
| | - Velia M Fowler
- Department of Cell and Molecular Biology, The Scripps Research Institute;
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18
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Bahrami M, Hoshino M, Pierscionek B, Yagi N, Regini J, Uesugi K. Refractive index degeneration in older lenses: A potential functional correlate to structural changes that underlie cataract formation. Exp Eye Res 2015; 140:19-27. [PMID: 26297613 DOI: 10.1016/j.exer.2015.08.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Revised: 07/20/2015] [Accepted: 08/12/2015] [Indexed: 10/23/2022]
Abstract
A major structure/function relationship in the eye lens is that between the constituent proteins, the crystallins and the optical property of refractive index. Structural breakdown that leads to cataract has been investigated in a number of studies; the concomitant changes in the optics, namely increases in light attenuation have also been well documented. Specific changes in the refractive index gradient that cause such attenuation, however, are not well studied because previous methods of measuring refractive index require transparent samples. The X-ray Talbot interferometric method using synchrotron radiation allows for measurement of fine changes in refractive index through lenses with opacities. The findings of this study on older human lenses show disruptions to the refractive index gradient and in the refractive index contours. These disruptions are linked to location in the lens and occur in polar regions, along or close to the equatorial plane or in lamellar-like formations. The disruptions that are seen in the polar regions manifest branching formations that alter with progression through the lens with some similarity to lens sutures. This study shows how the refractive index gradient, which is needed to maintain image quality of the eye, may be disturbed and that this can occur in a number of distinct ways. These findings offer insight into functional changes to a major optical parameter in older lenses. Further studies are needed to elicit how these may be related to structural degenerations reported in the literature.
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Affiliation(s)
- Mehdi Bahrami
- Faculty of Science, Engineering and Computing, Kingston University London, Kingston-upon-Thames, KT1 2EE, United Kingdom
| | - Masato Hoshino
- Japan Synchrotron Radiation Research Institute (SPring-8), Sayo, Hyogo, Japan
| | - Barbara Pierscionek
- Faculty of Science, Engineering and Computing, Kingston University London, Kingston-upon-Thames, KT1 2EE, United Kingdom.
| | - Naoto Yagi
- Japan Synchrotron Radiation Research Institute (SPring-8), Sayo, Hyogo, Japan
| | - Justyn Regini
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Kentaro Uesugi
- Japan Synchrotron Radiation Research Institute (SPring-8), Sayo, Hyogo, Japan
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19
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Nibourg LM, Sharma PK, van Kooten TG, Koopmans SA. Changes in lens stiffness due to capsular opacification in accommodative lens refilling. Exp Eye Res 2015; 134:148-54. [PMID: 25704214 DOI: 10.1016/j.exer.2015.02.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2014] [Revised: 02/17/2015] [Accepted: 02/18/2015] [Indexed: 12/19/2022]
Abstract
Accommodation may be restored to presbyopic lenses by refilling the lens capsular bag with a soft polymer. After this accommodative lens refilling prevention of capsular opacification is a requirement, since capsular opacification leads to a decreased clarity of the refilled lens. It has been hypothesized that capsular fibrosis causing the capsular opacification results in increased stiffness of the lens capsular bag, therewith contributing to a decrease in accommodative amplitude of the lens. However, the change in viscoelastic properties of refilled lenses due to capsular fibrosis has never been measured directly. In this study we examined natural lenses from enucleated porcine eyes and refilled lenses directly after refilling and after three months of culturing, when capsular fibrosis had developed, and determined their viscoelastic properties with a low load compression tester. Control refilled lenses were included in which capsular opacification was prevented by treatment with actinomycin D. We related lens stiffening to the degree of capsular opacification, as derived from the microscopic images taken with a confocal laser scanning microscope. Overall, the refilled lenses directly after refilling were softer than refilled lenses after three months of culturing, and refilled lenses treated with actinomycin D were softer compared with untreated refilled lenses. The degree of capsular opacification as assessed by microscopy corresponds to an increase in lens stiffness. This indicates that the viscoelastic properties of the refilled lens are influenced by capsular fibrosis and modulated by treatment of the lens epithelium. In conclusion, this study shows that the development of capsular fibrosis negatively affects the viscoelastic properties of isolated, cultured refilled lenses.
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Affiliation(s)
- Lisanne M Nibourg
- University of Groningen, University Medical Center Groningen, Dept. of Ophthalmology, Hanzeplein 1, 9713 GZ Groningen, The Netherlands; University of Groningen, University Medical Center Groningen, Laboratory for Experimental Ophthalmology, Hanzeplein 1, 9713 GZ Groningen, The Netherlands; University of Groningen, University Medical Center Groningen, W.J. Kolff Institute, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands.
| | - Prashant K Sharma
- University of Groningen, University Medical Center Groningen, W.J. Kolff Institute, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands; University of Groningen, University Medical Center Groningen, Dept. of Biomedical Engineering, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands
| | - Theo G van Kooten
- University of Groningen, University Medical Center Groningen, W.J. Kolff Institute, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands; University of Groningen, University Medical Center Groningen, Dept. of Biomedical Engineering, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands
| | - Steven A Koopmans
- University of Groningen, University Medical Center Groningen, Dept. of Ophthalmology, Hanzeplein 1, 9713 GZ Groningen, The Netherlands; University of Groningen, University Medical Center Groningen, W.J. Kolff Institute, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands
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20
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Abstract
PURPOSE To investigate porcine lenses in a lens stretcher with regard to presbyopia corrective procedures. METHODS A lens stretching device was designed, which allows to simultaneously determine all relevant geometrical and optical parameters at each stretch position. The setup was used to compare the optical and geometrical lens properties of young slaughter pigs (n = 5) with older sows (n = 7). RESULTS The change of optical power with stretching is about five times larger for young porcine lenses than for sows. For young pigs, the gradient index profile of the crystalline lens significantly contributes to the induced accommodation amplitude. CONCLUSIONS We have shown that sow lenses are a suitable model for in vitro experiments on possible treatments for presbyopia. The rapid decrease in the induced accommodation amplitude with age may be explained by a reduced change of all geometrical lens parameters, which in turn leads to a smaller contribution of the gradient index profile to accommodation.
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21
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Abstract
PURPOSE To investigate the morphology of the ciliary muscle during the act of accommodation in a population of children. METHODS Thirty children aged 6 to 12 years were enrolled. Accommodative response was measured through habitual correction. Height was measured as a control variable. Central axial length was measured with the IOLMaster. Four images of the temporal ciliary muscle were taken with the Visante Optical Coherence Tomographer at three different stimulus levels (0, 4, and 6 D) while accommodative response was monitored concurrently with the PowerRefractor. Accommodative response monitoring was time-matched to ciliary muscle image capture, and the mean was calculated for 5 s surrounding this time point. Four cycloplegic images of the temporal ciliary muscle were also taken. Ciliary muscle thickness measurements were made at the point of maximum thickness (CMTMAX) and at 1 mm (CMT1), 2 mm (CMT2) and 3 mm (CMT3) posterior to the sclera spur. RESULTS Increasing accommodative response was correlated with increases in the thickness of CMTMAX (p = <0.001) and CMT1 (p = <0.001) and decreases in the thickness of CMT3 (p = <0.001). Thicker values of CMTMAX under cycloplegic conditions were significantly correlated with values of CMTMAX (p = <0.001) and CMT1 (p = 0.001) while accommodating and approached significance in modeling CMT3 (p = 0.06). Mean axial length was correlated with the amount of thinning at CMT3 with accommodation (p = 0.002). Axial length was not significantly correlated with thickness values at CMTMAX (p = 0.7) or CMT1 (p = 0.6). CONCLUSIONS In a manner similar to previous adult studies, ciliary muscle thickness at CMTMAX and CMT1 increased with accommodation and CMT3 thinned with accommodation. Further investigation is necessary to determine whether CMT2 is a "fulcrum" point along the length of the ciliary muscle where the net change with accommodation is always zero or whether that point varies across subjects or with varying levels of accommodative effort.
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22
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Augusteyn RC, Mohamed A, Nankivil D, Veerendranath P, Arrieta E, Taneja M, Manns F, Ho A, Parel JM. Age-dependence of the optomechanical responses of ex vivo human lenses from India and the USA, and the force required to produce these in a lens stretcher: the similarity to in vivo disaccommodation. Vision Res 2011; 51:1667-78. [PMID: 21658404 DOI: 10.1016/j.visres.2011.05.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2011] [Revised: 05/16/2011] [Accepted: 05/17/2011] [Indexed: 11/25/2022]
Abstract
The purpose of this study was to study the age-dependence of the optomechanical properties of human lenses during simulated disaccommodation in a mechanical lens stretcher, designed to determine accommodative forces as a function of stretch distance, to compare the results with in vivo disaccommodation and to examine whether differences exist between eyes harvested in the USA and India. Postmortem human eyes obtained in the USA (n=46, age=6-83 years) and India (n=91, age=1 day-85 years) were mounted in an optomechanical lens stretching system and dissected to expose the lens complete with its accommodating framework, including zonules, ciliary body, anterior vitreous and a segmented rim of sclera. Disaccommodation was simulated through radial stretching of the sectioned globe by 2mm in increments of 0.25 mm. The load, inner ciliary ring diameter, lens equatorial diameter, central thickness and power were measured at each step. Changes in these parameters were examined as a function of age, as were the dimension/load and power/load responses. Unstretched lens diameter and thickness increased over the whole age range examined and were indistinguishable from those of in vivo lenses as well as those of in vitro lenses freed from zonular attachments. Stretching increased the diameter and decreased the thickness in all lenses examined but the amount of change decreased with age. Unstretched lens power decreased with age and the accommodative amplitude decreased to zero by age 45-50. The load required to produce maximum stretch was independent of age (median 80 mN) whereas the change in lens diameter and power per unit load decreased significantly with age. The age related changes in the properties of human lenses, as observed in the lens stretching device, are similar to those observed in vivo and are consistent with the classical Helmholtz theory of accommodation. The response of lens diameter and power to disaccommodative (stretching) forces decreases with age, consistent with lens nuclear stiffening.
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Affiliation(s)
- Robert C Augusteyn
- Vision Cooperative Research Centre, Brien Holden Vision Institute, Sydney, Australia.
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23
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Higher-order ocular aberrations caused by crystalline lens waterclefts. J Cataract Refract Surg 2010; 36:799-805. [PMID: 20457372 DOI: 10.1016/j.jcrs.2009.12.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Revised: 11/30/2009] [Accepted: 12/01/2009] [Indexed: 11/23/2022]
Abstract
PURPOSE To compare visual acuity and ocular higher-order aberrations (HOAs) in eyes with waterclefts, a type of crystalline lens opacity, and in normal eyes. SETTING Department of Ophthalmology, Kanazawa Medical University, Ishikawa, Japan, and Faculty of Medicine, University of Iceland, Reykjavik, Iceland. METHODS In this nested case-control study of subjects attending the third examination of the Reykjavik Eye Study in 2008, eyes with pure waterclefts and control eyes with no lenticular opacity were evaluated. All candidates had complete ophthalmic examinations and wavefront analysis. Higher-order aberrations in the watercleft group and the control group were compared. RESULTS The watercleft group comprised 30 eyes and the control group, 194 eyes. The mean corrected distance visual acuity (CDVA) in the watercleft group was statistically significantly lower than in the control group (P<.01). There was a significant relationship between CDVA and HOA in both groups. Total HOA and trefoil and coma aberrations were statistically significantly higher in the watercleft group than in the control group (P<.05). CONCLUSIONS Waterclefts significantly affected CDVA. Eyes with waterclefts had higher coma and trefoil aberrations, suggesting that the increased HOAs caused reduced visual acuity in eyes with waterclefts.
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24
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Smith G, Atchison DA, Robert Iskander D, Jones CE, Pope JM. Mathematical models for describing the shape of the in vitro unstretched human crystalline lens. Vision Res 2009; 49:2442-52. [DOI: 10.1016/j.visres.2009.07.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2009] [Revised: 07/21/2009] [Accepted: 07/27/2009] [Indexed: 10/20/2022]
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25
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Reilly MA, Hamilton PD, Perry G, Ravi N. Comparison of the behavior of natural and refilled porcine lenses in a robotic lens stretcher. Exp Eye Res 2008; 88:483-94. [PMID: 19041865 DOI: 10.1016/j.exer.2008.10.021] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2008] [Revised: 09/19/2008] [Accepted: 10/30/2008] [Indexed: 11/18/2022]
Abstract
The mechanism by which the eye dynamically changes focal distance (accommodation), and the mechanism by which this ability is lost with age (presbyopia), are still contested. Due to inherent confounding factors in vivo, in vitro measurements have been undertaken using a robotic lens stretcher to examine these mechanisms as well as the efficacy of lens refilling - a proposed treatment for presbyopia. Dynamic forces, anterior and posterior curvatures, and lens thickness are all correlated for young natural and refilled porcine lenses. Comparisons are made to lenses refilled with a homogeneous polymer system. The amplitude of accommodation of the young porcine lens is very small such that it may be a suitable model for presbyopia. The behavior of refilled lenses was highly dependent on the refill volume. The volume could be tuned to maximize accommodative amplitude in the refilled lens.
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Affiliation(s)
- Matthew A Reilly
- Department of Veterans Affairs Medical Center JC, Washington University in St Louis, St Louis, MO 63110, USA.
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26
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Richdale K, Bullimore MA, Zadnik K. Lens thickness with age and accommodation by optical coherence tomography. Ophthalmic Physiol Opt 2008; 28:441-7. [PMID: 18761481 PMCID: PMC2857534 DOI: 10.1111/j.1475-1313.2008.00594.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
PURPOSE To utilize time-domain optical coherence tomography (OCT) to measure changes in the crystalline lens with age and accommodation. METHODS A cross-sectional study of pre-presbyopic and presbyopic subjects was conducted. Amplitude of accommodation was measured with the push-up test. Objective accommodation was measured with the Grand Seiko auto-refractor and a Badal lens system. Lens thickness was measured with the Zeiss Visante OCT and an internal optometer. The data were analysed using correlation coefficients, linear regression, and by calculating the average change in lens thickness per diopter change in objective accommodation. RESULTS Twenty-two subjects between the ages of 36 and 50 years completed the study. Subjective amplitude of accommodation ranged from 2.17 to 6.38 D. Objective accommodation ranged from 0.22 to 4.56 D. The mean lens thickness was 4.05+/-0.20 mm. The mean change in lens thickness for up to a 5-D accommodative stimulus ranged from 0.01 to 0.26 mm. The correlation coefficients were: age and subjective accommodation, r= -0.74; age and objective accommodation, r= -0.84; change in lens thickness and age, r= -0.65; change in lens thickness and subjective accommodation, r=0.74; change in lens thickness and objective accommodation, r=0.64; objective and subjective accommodation, r=0.82 (all p<0.01). An increase in lens thickness of 21 microm per year of age was determined by linear regression. For the subjects who showed at least 1 D of accommodative response on the Grand Seiko auto-refractor, there was an increase of 51+/-19 microm per dioptre of accommodation. CONCLUSIONS Optical coherence tomography is a non-invasive technique that can be used to quantify changes in the thickness of the crystalline lens. Subjective and objective measurements of accommodation, as well as age, were robustly correlated with the measured changes in lens thickness. Lens thickness changes with age and accommodation as measured with the Visante OCT compare well with previous findings using Scheimpflug photography and ultrasound.
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Affiliation(s)
- Kathryn Richdale
- The Ohio State University College of Optometry, 338 West 10th Avenue, Columbus, OH 43210, USA.
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27
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Dynamic multi-arm radial lens stretcher: A robotic analog of the ciliary body. Exp Eye Res 2008; 86:157-64. [DOI: 10.1016/j.exer.2007.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2007] [Revised: 10/12/2007] [Accepted: 10/16/2007] [Indexed: 11/23/2022]
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28
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Manns F, Parel JM, Denham D, Billotte C, Ziebarth N, Borja D, Fernandez V, Aly M, Arrieta E, Ho A, Holden B. Optomechanical response of human and monkey lenses in a lens stretcher. Invest Ophthalmol Vis Sci 2007; 48:3260-8. [PMID: 17591897 PMCID: PMC3429371 DOI: 10.1167/iovs.06-1376] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To quantify the forces necessary to change the shape and optical power of human and monkey lenses. METHODS Cynomolgus monkey (n = 48; age: 3.8-11 years), rhesus monkey (n = 35; age: 0.7-17 years) and human (n = 20, age 8-70 years) eyes obtained postmortem, including the lens, capsule, zonules, ciliary body, and sclera were mounted in an optomechanical lens-stretching system. Starting at zero load, the lenses were symmetrically stretched in a stepwise fashion in 0.25- or 0.5-mm steps. The load, lens diameter, inner ciliary body diameter, and lens power were measured at each step and the diameter- and power-load responses were quantified. RESULTS The diameter- and power-load responses were found to be linear in the physiologically relevant range of stretching. The average change in cynomolgus, rhesus, and human lens diameter, respectively, was 0.094, 0.109, and 0.069 mm/g in young lenses, and 0.069, 0.067, and 0.036, mm/g in older lenses. For the same lenses, the average change in lens power was -3.73, -2.83, and -1.22 D/g in young lenses and -2.46, -2.16, and -0.49 D/g in older lenses. CONCLUSIONS The force necessary to change the lens diameter and lens power increases with age in human and monkey lenses. The results agree with the Helmholtz theory of accommodation and with presbyopia theories that predict that the force required to disaccommodate the lens increases with age.
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Affiliation(s)
- Fabrice Manns
- Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida 33136, USA.
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29
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Weeber HA, van der Heijde RGL. On the relationship between lens stiffness and accommodative amplitude. Exp Eye Res 2007; 85:602-7. [PMID: 17720158 DOI: 10.1016/j.exer.2007.07.012] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2007] [Revised: 06/22/2007] [Accepted: 07/14/2007] [Indexed: 11/30/2022]
Abstract
The purpose of this study was to investigate the relationship between the stiffness of the material comprising the lens and the loss of accommodative amplitude with age. We used a validated mechanical model to determine the changes in the shape of the lens during accommodation and disaccommodation. The relative contribution of lens stiffness to loss of accommodative amplitude with age was determined by varying lens stiffness in the model. The changes in lens stiffness with age were based on the results of two recently published studies. In the first study we showed that lens stiffness increases exponentially with age, and in the second study we showed that there is a considerable stiffness gradient within the lens that changes with age. The results of both studies were incorporated in the mechanical model. The model showed that it is not the increasing stiffness of the lens with age, but rather the changing stiffness gradient that influences accommodative amplitude. The results show that the changing stiffness gradient in the lens may be responsible for almost the entire loss of accommodation with age.
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Affiliation(s)
- Henk A Weeber
- AMO Groningen, van Swietenlaan 5, 9728 NX Groningen, The Netherlands.
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30
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Abstract
Most of the optical models of the human eye use simple conic functions to represent its individual components such as corneal surfaces and the surfaces of the crystalline lens. Although a conic function provides an acceptable approximation for most anatomical eye surfaces, it also leads to a simple optical analysis of the whole eye system. To fill the gap between the classical use of conic surfaces and the use of more sophisticated functions that often invoke numerically expensive procedures in the optical analysis, a functional generalisation of the conic curve is proposed. A detailed derivation of the generalised conic function is presented for a two-dimensional (meridional) case. This is followed by a three-dimensional surface approximation. Examples are given in which the superiority of the proposed approximation over a classical conic function as well as the hyperbolic cosine approximation is evident. In particular, it is shown that for an average total corneal profile, the proposed generalisation results in a residual height error that is of an order smaller than those achieved with the conic and hyperbolic cosine approximations. In conclusion, the proposed generalised conic function can be a useful tool in eye modelling, where the simplicity of expression is often desirable.
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31
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Weeber HA, Eckert G, Pechhold W, van der Heijde RGL. Stiffness gradient in the crystalline lens. Graefes Arch Clin Exp Ophthalmol 2007; 245:1357-66. [PMID: 17285335 DOI: 10.1007/s00417-007-0537-1] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2006] [Revised: 01/10/2007] [Accepted: 01/14/2007] [Indexed: 10/23/2022] Open
Abstract
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 degrees 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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Affiliation(s)
- Henk A Weeber
- AMO, Van Swietenlaan 5, 9728 NX Groningen, The Netherlands.
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32
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Erpelding TN, Hollman KW, O'Donnell M. Mapping age-related elasticity changes in porcine lenses using bubble-based acoustic radiation force. Exp Eye Res 2006; 84:332-41. [PMID: 17141220 PMCID: PMC1829319 DOI: 10.1016/j.exer.2006.10.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2006] [Revised: 09/29/2006] [Accepted: 10/05/2006] [Indexed: 10/23/2022]
Abstract
Bubble-based acoustic radiation force aims to measure highly localized tissue viscoelastic properties. In the current investigation, acoustic radiation force was applied to laser-induced bubbles to measure age-related changes in the spatial distribution of elastic properties within in vitro porcine lenses. A potential in vivo technique to map lens elasticity is crucial to understanding the onset of presbyopia and develop new treatment options. Bubble-based acoustic radiation force was investigated as a technique to measure the spatial elasticity distribution of the lens in its natural state without disrupting the lens capsule. Laser-induced optical breakdown (LIOB) generated microbubbles in a straight line across the equatorial plane of explanted porcine lenses with 1mm lateral spacing. Optical breakdown occurs when sufficiently high threshold fluence is attained at the focus of femtosecond pulsed lasers, inducing plasma formation and bubble generation. A two-element confocal ultrasonic transducer applied 6.5 ms acoustic radiation force-chirp bursts with the 1.5 MHz outer element while monitoring bubble position within the lens using pulse-echoes with the 7.44 MHz inner element. A cross-correlation method was used to measure bubble displacements and determine exponential time constants of the temporal responses. Maximum bubble displacements are inversely proportional to the local Young's modulus, while time constants are indicative of viscoelastic properties. The apparent spatial elasticity distributions in 41 porcine lenses, ranging from 4 months to 5 years in age, were measured using bubble-based acoustic radiation force. Bubble displacements decrease closer to the porcine lens center, suggesting that the nucleus is stiffer than the cortex. Bubble displacements decrease with increasing lens age, suggesting that porcine lenses become stiffer with age. Bubble-based acoustic radiation force may be well-suited as a potential in vivo technique to spatially map elastic properties of the lens and guide therapeutic procedures aimed at restoring accommodation.
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Affiliation(s)
- Todd N Erpelding
- Department of Biomedical Engineering, University of Michigan, 2200 Bonisteel Boulevard, 1107 Gerstacker Building, Ann Arbor, MI 48109-2099, USA.
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33
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Pau H. Cortical and subcapsular cataracts: significance of physical forces. Ophthalmologica 2006; 220:1-5. [PMID: 16374041 DOI: 10.1159/000089267] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2005] [Accepted: 07/01/2005] [Indexed: 11/19/2022]
Abstract
Cortical cataracts usually begin with either sharp limited clear fluid clefts, resulting in opaque spokes, or clear lamellar separations, resulting in cuneiform opacities. They do not commence prior to 45 years of age. From this age on an increase in lens nuclei hardening can be detected. Therefore, during disaccommodation in older lenses, mechanical shear stresses must develop between the soft remaining cortices and the harder nuclei. These shear stresses are significant regarding the different cortical ruptures in predisposed lenses: in a privileged radial direction (according to zonular traction) of the sharp limited cortical spokes, or in parallel microridges at the commencement of lamellar separations, as observed when a rubber surface slides against a harder object. In pure cortical cataracts the ion pump (K+ > Na+) and investigated metabolic parameters remain largely intact. Therefore, it is not surprising that, in contrast to subcapsular cataracts, subcapsular opacities do not occur. Subcapsular cataracts are known to be caused by a variety of factors: aging, diabetes, corticosteroids, iridocyclitis, or X-ray, among many others. In contrast to cortical cataracts, subcapsular cataracts were found to be closely associated with ion pump damage (Na+ > K+) and a variety of metabolic activity alterations. In subcapsular cataracts passive fluids (from the vitreous and camera anterior) enter externally through the lens capsule. This initially forms numerous free clear, secondary grey, subcapsular fluid vacuoles. If the ion pump (metabolic barrier) is more severely damaged fluids may also enter the lens nucleus (secondary grey nuclear cataract), which rarely results in intumescent cataract. In cortical and subcapsular cataracts and lens perforations the main cause of grey opalescence appears to be the result of lens proteins (water-soluble crystalline) coming into direct contact with free fluids (water). In cortical cataracts this happens in the area of sharp limited mechanical cortical ruptures (fluid clefts), and in subcapsular cataracts during passive, external fluid entry, resulting in subcapsular fluid vacuoles and opacities, and also later grey-white nuclear opacities. The importance of water contact with water-soluble lens crystallines in behalf of light scattering and turbidness also has been investigated experimentally.
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Affiliation(s)
- Hans Pau
- Department of Ophthalmology, Heinrich Heine University, Dusseldorf, Germany.
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34
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McGinty SJ, Truscott RJW. Presbyopia: the first stage of nuclear cataract? Ophthalmic Res 2006; 38:137-48. [PMID: 16397406 DOI: 10.1159/000090645] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Accepted: 11/08/2005] [Indexed: 11/19/2022]
Abstract
Presbyopia, the inability to accommodate, affects almost everyone at middle age. Recently, it has been shown that there is a massive increase in the stiffness(1) of the lens with age and, since the shape of the lens must change during accommodation, this could provide an explanation for presbyopia. In this review, we propose that presbyopia may be the earliest observable symptom of age-related nuclear (ARN) cataract. ARN cataract is a major cause of world blindness. The genesis of ARN cataract can be traced to the onset of a barrier within the lens at middle age. This barrier restricts the ability of small molecules, such as antioxidants, to penetrate into the centre of the lens leaving the proteins in this region susceptible to oxidation and post-translational modification. Major protein oxidation and colouration are the hallmarks of ARN cataract. We postulate that the onset of the barrier, and the hardening of the nucleus, are intimately linked. Specifically, we propose that progressive age-dependent hardening of the lens nucleus may be responsible for both presbyopia and ARN cataract.
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Affiliation(s)
- S J McGinty
- Save Sight Institute, Sydney, and Institute for Biomolecular Science, University of Wollongong, Wollongong, Australia
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35
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Abstract
Accommodation in humans refers to the ability of the lens to change shape in order to bring near objects into focus. Accommodative loss begins during childhood, with symptomatic presbyopia, or presbyopia that affects one's day to day activities, striking during midlife. While symptomatic presbyopia has traditionally been treated with reading glasses or contact lenses, a number of surgical interventions and devices are being actively developed in an attempt to restore at least some level of accommodation. This is occurring at a time when the underlying cause of presbyopia remains unknown, and even the mechanism of accommodation is occasionally debated. While Helmholtz' theory regarding the mechanism of accommodation is generally accepted with regard to broad issues, additional details continue to emerge. Age-related changes in anterior segment structures associated with accommodation have been documented, often through in vitro and/or rhesus monkey studies. A review of these findings suggests that presbyopia develops very differently in humans compared to non-human primates. Focusing on non-invasive in vivo human imaging technologies, including Scheimpflug photography and high-resolution magnetic resonance imaging (MRI), the data suggest that the human uveal tract acts as a unit in response to age-related increasing lens thickness and strongly implicates lifelong lens growth as the causal factor in the development of presbyopia.
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Affiliation(s)
- Susan A Strenk
- Department of Surgery, Robert Wood Johnson Medical School-University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08855, USA
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36
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Weeber HA, Eckert G, Soergel F, Meyer CH, Pechhold W, van der Heijde RGL. Dynamic mechanical properties of human lenses. Exp Eye Res 2005; 80:425-34. [PMID: 15721624 DOI: 10.1016/j.exer.2004.10.010] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2004] [Accepted: 10/20/2004] [Indexed: 11/17/2022]
Abstract
The purpose of this study was to determine the shear compliance of human crystalline lenses as a function of age and frequency. Dynamic mechanical analysis was performed on 39 human lenses, ranging in age from 18 to 90 years, within the frequency range of 0.001-30 Hz. The lenses were stored at -70 degrees C before being measured. The influence of freezing on the mechanical properties was determined using pairs of porcine lenses, with one lens measured directly after enucleation and the other after freezing. The measurement method had a repeatability standard deviation of 4 and 6% for the storage and loss compliance, respectively. The reproducibility standard deviation was 31 and 33% for the storage and loss compliance respectively. On average, freezing increased the storage compliance by 8% and increased the loss compliance by 32%, both depending slightly on age and frequency. The human lenses exhibited a distinct viscoelastic behavior. The storage and loss compliance depended strongly on age and decreased a factor 1000 over a lifetime. Dynamic mechanical analysis has proven to be a successful technique for characterizing the mechanical properties of the human crystalline lens. The shear compliance decreases exponentially with age.
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Affiliation(s)
- Henk A Weeber
- Applied Research, AMO Groningen b.v., P.O. Box 901, 9700 NX, Groningen, The Netherlands.
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37
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Manns F, Fernandez V, Zipper S, Sandadi S, Hamaoui M, Ho A, Parel JM. Radius of curvature and asphericity of the anterior and posterior surface of human cadaver crystalline lenses. Exp Eye Res 2004; 78:39-51. [PMID: 14667826 DOI: 10.1016/j.exer.2003.09.025] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The purpose of this study was to measure the shape of the anterior and posterior surface of human cadaver lenses in situ using a corneal topography system. Measurements were performed on 13 pairs of eyes using the PAR Corneal Topography System (PAR-CTS). The age of the donors ranged from 46 to 93 years, with an average age of 76.4 years. Anterior lens topography was measured after excision of the cornea and iris. Posterior lens topography was measured after sectioning the posterior segment and adherent vitreous. The PAR-CTS files providing raw surface height were exported for analysis. In each surface, 18 meridians separated by 10 degrees were fitted using conic sections to obtain values of the apical radius of curvature (R) and shape factor (p). The average apical radius of curvature and asphericity were R=10.15+/-1.39mm and p=4.27+/-1.39 for the anterior surface and R=-6.25+/-0.79mm and p=-0.64+/-1.85 for the posterior surface. A significant variation of the radius of curvature and shape factor as a function of the meridian angle (lens astigmatism) was found in some lenses. Contrary to previous findings, the anterior lens surface was found to steepen toward the periphery.
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Affiliation(s)
- Fabrice Manns
- Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami School of Medicine, 1638 NW 10th Avenue, Miami, FL 33136, USA.
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38
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Abstract
Data on geometric and material properties of the human lens derived from various published sources are used to construct axisymmetric, large displacement, finite element models of the accommodating lens of subjects aged 11, 29 and 45 years. The nucleus, cortex, capsule and zonule are modelled as linearly elastic materials. The numerical model of the 45-year lens is found to be significantly less effective in accommodating than the 29-year lens, suggesting that the modelling procedure is capable of capturing at least some of the features of presbyopia. The model of the 11-year lens shows some anomalous behaviour, and reasons for this are explored.
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Affiliation(s)
- H J Burd
- Department of Engineering Science, University of Oxford, Parks Road, OX1 3PJ, Oxford, UK.
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39
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Murthy SK, Ravi N. Hydrogels as potential probes for investigating the mechanism of lenticular presbyopia. Curr Eye Res 2001; 22:384-93. [PMID: 11600940 DOI: 10.1076/ceyr.22.5.384.5493] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
PURPOSE To synthesize and characterize hydrogels with viscoelastic properties comparable to those of the natural lens. METHODS Hydrogels were synthesized in water by free-radical polymerization of the monomer poly(ethyleneglycol)-monomethacrylate. Three different molecular weights of poly(ethyleneglycol)-dimethacrylates were used as crosslinkers. For each crosslinker used, five different monomer-to-crosslinker weight ratios were utilized while the total mass of the reactants was kept constant. In another series, the concentration of the reactants was varied while the weight ratio of monomer to crosslinker was kept constant at 95 : 5. The percent optical transmission, equilibrium water content, moduli (elastic, shear, storage, and loss), and retardation time constant of the hydrogels were determined. In addition, endocapsular polymerization was performed in the capsular bag of porcine eyes. RESULTS The hydrogels examined exhibited the following ranges for viscoelastic properties: elastic modulus, 1.33-2.37 x 10(4) Pa; shear modulus, 3.35-6.72 x 10(3) Pa; storage modulus, 1.65-6.24 x 10(4) Pa. For any given hydrogel, raising its crosslinker's weight ratio increased its moduli and decreased its equilibrium water content and optical transmission. For any given monomer-to-crosslinker weight ratio, increasing the molecular weight of the crosslinker reversed these trends. Reactant concentrations increased the elastic modulus and decreased the equilibrium water content. The hydrogels formed ex vivo (in the evacuated capsular bag of porcine eyes) allowed for the clear and undistorted viewing of objects. CONCLUSIONS Hydrogels that exhibit physical and mechanical properties comparable to those of the natural lens were successfully identified, synthesized, and characterized, and the feasibility of endocapsular polymerization was demonstrated.
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Affiliation(s)
- S K Murthy
- Department of Surgery, Veterans Affairs Medical Center, Ophthalmology Service, St. Louis, MO 63106, USA
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40
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Glasser A, Campbell MC. Biometric, optical and physical changes in the isolated human crystalline lens with age in relation to presbyopia. Vision Res 1999; 39:1991-2015. [PMID: 10343784 DOI: 10.1016/s0042-6989(98)00283-1] [Citation(s) in RCA: 252] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
The biometric, optical and physical properties of 19 pairs of isolated human eye-bank lenses ranging in age from 5 to 96 years were compared. Lens focal length and spherical aberration were measured using a scanning laser apparatus, lens thickness and the lens surface curvatures were measured by digitizing the lens profiles and equivalent refractive indices were calculated for each lens using this data. The second lens from each donor was used to measure resistance to physical deformation by providing a compressive force to the lens. The lens capsule was then removed from each lens and each measurement was repeated to ascertain what role the capsule plays in determining these optical and physical characteristics. Age dependent changes in lens focal length, lens surface curvatures and lens resistance to physical deformation are described. Isolated lens focal length was found to be significantly linearly correlated with both the anterior and posterior surface curvatures. No age dependent change in equivalent refractive index of the isolated lens was found. Although decapsulating human lenses causes similar changes in focal length to that which we have shown to occur when human lenses are mechanically stretched into an unaccommodated state, the effects are due to nonsystematic changes in lens curvatures. These studies reinforce the conclusion that lens hardening must be considered as an important factor in the development of presbyopia, that age changes in the human lens are not limited to the loss of accommodation that characterizes presbyopia but that the lens optical and physical properties change substantially with age in a complex manner.
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Affiliation(s)
- A Glasser
- College of Optometry, University of Houston, TX 77204, USA.
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