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Zhang G, Jiang J, Wei Q, Qu C. Effects of accommodation on geometrical parameters of human lens: A systematic review and meta-analysis. Heliyon 2024; 10:e29298. [PMID: 38681553 PMCID: PMC11053204 DOI: 10.1016/j.heliyon.2024.e29298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2023] [Revised: 03/29/2024] [Accepted: 04/04/2024] [Indexed: 05/01/2024] Open
Abstract
Purpose To investigate the effects of accommodation on the geometrical parameters of human lens. Methods Eight databases from inception to November 2023 were used for the literature search: CNKI, CBM, VIP, Wan-Fang, PubMed, Web of Science, EMBASE, and the Cochrane Library. The Methodological Index for Non-randomized Studies was used to assess the risk of bias. The PRISMA were followed and the following outcomes were taken into consideration: lens diameter (LD), lens thickness (LT), anterior curvature radius (ACR), posterior curvature radius (PCR), lens center position (LCP), and total cross-sectional area (TCSA). This systematic review was registered on an international platform for registered systematic reviews and meta-analysis (INPLASY202260085). Results A total of 19 studies were included. LT increased by 0.04 mm/D (18 studies; 95% confidence interval [CI], 0.03-0.06; I2 = 96.6%; P < 0.001). At the same time, LD, ACR, and PCR decreased by 0.06 mm/D (6 studies; 95%CI, -0.07-0.05; I2 = 50.1%; P < 0.001), 0.53 mm/D (8 studies; 95%CI, -0.64-0.41; I2 = 96.5%; P < 0.001), and 0.14 mm/D (9 studies; 95%CI, -0.19-0.09; I2 = 94.7%; P < 0.001) during accommodation, respectively. Moreover, LCP shifted forward by 0.01 mm/D (3 studies; 95%CI, -0.02-0.00; I2 = 0.0%; P < 0.001), and TCSA by 0.58 mm2/D (2 studies; 95%CI, 0.41-1.57; I2 = 97.0%; P = 0.457) during accommodation. Conclusions Changes in LT, LD, ACR, PCR and LCP supported Helmholtz's theory. Different apparatuses or measurement methods influenced the measurement of lens geometrical parameters.
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Affiliation(s)
- Guanghong Zhang
- Department of Ophthalmology, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN 611731, China
- School of Medicine, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN 611731, China
- Sichuan Key Laboratory for Disease Gene Study, Chinese Academy of Sciences Sichuan Translational Medicine Research Hospital, No. 32 of the West 2nd Section of First Ring Road, Chengdu 610072, China
| | - Jun Jiang
- Department of Ophthalmology, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN 611731, China
- School of Medicine, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN 611731, China
- Sichuan Key Laboratory for Disease Gene Study, Chinese Academy of Sciences Sichuan Translational Medicine Research Hospital, No. 32 of the West 2nd Section of First Ring Road, Chengdu 610072, China
| | - Qian Wei
- Southwest Medical University, No. 319, Section 3, Zhongshan Road, Luzhou 646000, China
| | - Chao Qu
- Department of Ophthalmology, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN 611731, China
- School of Medicine, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN 611731, China
- Sichuan Key Laboratory for Disease Gene Study, Chinese Academy of Sciences Sichuan Translational Medicine Research Hospital, No. 32 of the West 2nd Section of First Ring Road, Chengdu 610072, China
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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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Zhang G, Wei Q, Lu L, Lin AL, Qu C. The evolution of mechanism of accommodation and a novel hypothesis. Graefes Arch Clin Exp Ophthalmol 2023; 261:3083-3095. [PMID: 37103620 DOI: 10.1007/s00417-023-06045-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 01/06/2023] [Accepted: 03/24/2023] [Indexed: 04/28/2023] Open
Abstract
Myopia and presbyopia are two major optometry problems facing the whole society. The mechanism of accommodation is strongly related to the treatments of myopia and presbyopia. However, the key mechanism of accommodation has puzzled us for over 400 years and is still not clear at present, leading to the stagnation of prevention and treatment of myopia and presbyopia. With the continued development of experimental technologies and equipment, the approaches to elucidate accommodation's intricacies have become more methodological and sophisticated. Fortunately, some significant progress has been made. This article is to review the evolution of the mechanism of accommodation. Helmholtz proposed a classical theory of "zonules relax during accommodation." In contrast, Schachar put forward a theory of "zonules taut during accommodation." Those hypotheses are relatively complete, but either do not fully explain everything about the accommodation mechanism or lack sufficient experimental and clinical evidence to support them. Then, some contentious issues are discussed in detail to find the truth. Finally, we proposed our hypothesis about accommodation based on the anatomy of the accommodative apparatus.
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Affiliation(s)
- Guanghong Zhang
- School of Medicine, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN611731, China
- Department of Ophthalmology, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN611731, China
- Sichuan Key Laboratory for Disease Gene Study, Chinese Academy of Sciences Sichuan Translational Medicine Research Hospital, No. 32 of the West 2nd Section of First Ring Road, Chengdu, 610072, China
| | - Qian Wei
- Southwest Medical University, No. 319, Section 3, Zhongshan Road, Luzhou, 646000, China
| | - Lei Lu
- School and Hospital of Stomatology, Wenzhou Medical University, Xueyuan West Road, Wenzhou, Zhejiang, 325027, China.
| | - Andy L Lin
- Department of Internal Medicine, UC Irvine Medical Center, 333 City Blvd. West, Suite 400, Orange, CA, 92868-3298, USA.
| | - Chao Qu
- School of Medicine, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN611731, China.
- Department of Ophthalmology, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, No. 2006, Xiyuan Ave West Hi-Tech Zone, Chengdu, CN611731, China.
- Sichuan Key Laboratory for Disease Gene Study, Chinese Academy of Sciences Sichuan Translational Medicine Research Hospital, No. 32 of the West 2nd Section of First Ring Road, Chengdu, 610072, China.
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Cornaggia A, Clerici LM, Felizietti M, Rossi T, Pandolfi A. A numerical model of capsulorhexis to assess the relevance of size and position of the rhexis on the IOL decentering and tilt. J Mech Behav Biomed Mater 2020; 114:104170. [PMID: 33144045 DOI: 10.1016/j.jmbbm.2020.104170] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Accepted: 10/23/2020] [Indexed: 10/23/2022]
Abstract
Finite element models of human crystalline capsular bag and zonular fibers are used to estimate the mechanical response of the capsule to the presence of a C-loop Intra-Ocular Lens (IOL) after cataract surgery, to assess the influence of capsulorhexis size, shape and location on IOL decentration and tilt. The model includes, in the anterior capsule, a hole with variable size, shape and position, which represents the rhexis obtained in a manual or laser-assisted manner. The IOL is not explicitly modelled, but its action is reproduced by means of a set of elastic ties, connecting the opposite sides of the bag and exerting the force corresponding to an expanded IOL. Numerical simulations show that IOL decentration and tilt are not related to the size of the rhexis. A decentered rhexis induces IOL decentration <40 μm and a tilt <12°; the combination of non-circular shape and decentering of the rhexis induces IOL decentration <47 μm. While the introduction of a circular central rhexis causes an increment of the stresses in the capsule up to 100% relative to the physiological state, the combination of rhexis decentering and non-circular shape causes an additional 10% stress change. The values of IOL decentering and IOL tilt obtained from simulations are of scarce relevance in the clinical practice.
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Affiliation(s)
- Aram Cornaggia
- Politecnico di Milano, Civil and Environmental Engineering Department, Italy
| | - Laura M Clerici
- Politecnico di Milano, Chemistry, Materials, and Chemical Engineering Department, Italy
| | - Marta Felizietti
- Politecnico di Milano, Chemistry, Materials, and Chemical Engineering Department, Italy
| | | | - Anna Pandolfi
- Politecnico di Milano, Civil and Environmental Engineering Department, Italy.
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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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Jacobs MD. Multiscale systems integration in the eye. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2009; 1:15-27. [DOI: 10.1002/wsbm.29] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Marc D. Jacobs
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
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Current world literature. Curr Opin Ophthalmol 2008; 20:69-72. [PMID: 19077831 DOI: 10.1097/icu.0b013e32831fd89f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Schachar RA, Davila C, Pierscionek BK, Chen W, Ward WW. The effect of human in vivo accommodation on crystalline lens stability. Br J Ophthalmol 2007; 91:790-3. [PMID: 17215266 PMCID: PMC1955590 DOI: 10.1136/bjo.2006.110791] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AIM To determine the effect of human in vivo accommodation on the stability of the crystalline lens. METHODS Using a dual Purkinje image (DPI) eyetracker, the phase-time difference and amplitudes of Purkinje images I (P(I)) and IV (P(1V)) were measured in 37 normal emmetropic subjects (34 women and 3 men; mean age 19.8, range 18-22 years) when they changed focus from 70 to 15 cm and simultaneously rotated their heads horizontally from side to side or made horizontal saccades between two targets 6.8 degrees apart. RESULTS When the subjects changed focus from 70 to 15 cm and rotated their heads or made eye saccades, the phase-time difference between P(I) and P(IV) decreased. During saccades, the amplitude of both P(I) and P(IV) overshoots significantly increased with focus at 15 cm; however, their ratio (P(IV) overshoot amplitude/P(I) overshoot amplitude) significantly declined. CONCLUSIONS The lens is stable during accommodation. The implications of these findings on the mechanism of accommodation are discussed.
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Affiliation(s)
- Ronald A Schachar
- University of Texas at Arlington, PO Box 601149, Dallas, TX 75229, USA.
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Schachar RA, Pierscionek BK, Abolmaali A, Le T. The relationship between accommodative amplitude and the ratio of central lens thickness to its equatorial diameter in vertebrate eyes. Br J Ophthalmol 2006; 91:812-7. [PMID: 17050574 PMCID: PMC1955594 DOI: 10.1136/bjo.2006.107524] [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] [Indexed: 11/03/2022]
Abstract
AIM To determine the relationship between accommodative amplitude and central lens thickness/equatorial lens diameter (CLT/ELD) ratio in vertebrates. METHODS Midsagittal sections of lenses from fixed, post mortem eyes from 125 different vertebrate species were photographed. Their CLT/ELD ratios were correlated with independently published measurements of their accommodative amplitudes. Using the non-linear finite element method (FEM), the efficiency of zonular traction (the absolute change in central radius of curvature per unit force [|DeltaCR|/F]) for model lenses with CLT/ELD ratios from 0.45 to 0.9 was determined. RESULTS Vertebrates with CLT/ELD ratios < or =0.6 have high accommodative amplitudes. Zonular traction was found to be most efficient for those model lenses having CLT/ELD ratios < or =0.6. CONCLUSIONS Vertebrates with lenses that have CLT/ELD ratios < or =0.6--i.e. "long oval" shapes--have the greatest accommodative amplitudes; e.g. primates, diving birds and diurnal birds of prey. Vertebrates that have oval or spherical shaped lenses, like owls and most mammals, have low accommodative amplitudes. Zonular traction was found to be most efficient when applied to model lenses with CLT/ELD ratios < or =0.6. The implications of these findings on the mechanism of accommodation are discussed.
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Affiliation(s)
- Ronald A Schachar
- Department of Physics, University of Arlington, Arlington, Texas 76019, USA.
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