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      Age distribution and associated factors of cornea biomechanical parameter stress-strain index in Chinese healthy population

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          Abstract

          Background

          To investigate the new cornea biomechanical parameter stress-strain index (SSI) in Chinese healthy people and the factors associated with SSI.

          Methods

          A total of 175 eyes from 175 participants were included in this study. Axial length was measured with the Lenstar LS-900. Pentacam measured curvature of the cornea and anterior chamber volume (ACV). Cornea biomechanical properties assessments were performed by corneal visualization Scheimpflug technology (Corvis ST). Student’s t-test, one-way ANOVA, partial least square linear regression (PLSLR) and linear mixed effects (LME) model were used in the statistical analysis.

          Results

          The mean (±SD) SSI was 1.14 ± 0.22 (range, 0.66–1.78) in all subjects and affected by age significantly after age of 35 ( P < 0.05). In LME models, SSI was significantly associated with age (β = 0.526, P < 0.001), axial length (AL) (β = − 0.541, P < 0.001), intraocular pressure (IOP) (β = 0.326, P < 0.001) and steepest radius of anterior corneal curvature (RsF) (β = 0.229, P < 0.001) but not with ACV, biomechanical corrected intraocular pressure (bIOP), flattest radius of anterior corneal curvature (RfF) or central corneal thickness (CCT) ( P > 0.05 for each).

          Conclusions

          SSI increased with age after the age of 35. In addition to age, SSI was positively correlated with RsF and IOP, while negatively correlated with AL.

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          Most cited references49

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          Corneal biomechanical properties in normal, post-laser in situ keratomileusis, and keratoconic eyes.

          To compare the biomechanical properties of normal, post-laser in situ keratomileusis (LASIK), and keratoconic corneas evaluated by corneal hysteresis and the corneal resistance factor measured with the Reichert Ocular Response Analyzer (ORA). Instituto Oftalmológico de Alicante, Vissum, Alicante, Spain. Two hundred fifty eyes were divided into 3 groups: normal (control group), post-LASIK, and keratoconus. The corneal biomechanical properties were measured with the ORA, which uses a dynamic bidirectional applanation process. The main outcome measures were intraocular pressure, corneal hysteresis, and the corneal resistance factor. The control group had 165 eyes; the LASIK group, 65 eyes; and the keratoconus group, 21 eyes. In the control group, the mean corneal hysteresis value was 10.8 mm Hg +/- 1.5 (SD) and the mean corneal resistance factor, 11.0 +/- 1.6 mm Hg. The corneal hysteresis value was lower in older eyes, and the difference between the youngest age group (9 to 14 years) and oldest age group (60 to 80 years) was statistically significant (P = .01, t test). One month after LASIK, corneal hysteresis and the corneal resistance factor decreased significantly, from 10.44 to 9.3 mm Hg and from 10.07 to 8.13 mm Hg, respectively. In the keratoconus group, the mean corneal hysteresis was 7.5 +/- 1.2 mm Hg and the mean corneal resistance factor, 6.2 +/- 1.9 mm Hg. There were statistically significant differences in both biomechanical parameters between keratoconic eyes and post-LASIK eyes (P<.001, t test). The corneal hysteresis and corneal resistance factor values were significantly lower in keratoconic eyes than in post-LASIK eyes. Future work is needed to determine whether these differences are useful in detecting keratoconus when other diagnostic tests are equivocal.
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            Collagen fibrils in the human corneal stroma: structure and aging.

            Transparency and biomechanical properties of the cornea depend on the structure and organization of collagen fibrils. The authors determined diameter, axial period, and lateral molecular spacing of collagen fibrils in human corneal stroma as a function of age. Seventeen normal human corneas were investigated in their native state by means of small-angle and wide-angle x-ray scattering. The mean radius of collagen fibrils, the axial period of collagen fibrils, and the lateral intermolecular Bragg spacing were found to be age dependent. The authors determined fibril radii of 16.1 +/- 0.5 nm in persons older than 65 years of age (n = 10) and 15.4 +/- 0.5 nm (mean +/- SD) in persons younger than 65 years (n = 7) (P 65 years) and 65.2 +/- 0.8 nm ( 65 years) and 1.499 +/- 0.013 nm (< 65 years) for the intermolecular Bragg spacing (P < 0.022). Aging is related to a three-dimensional growth of collagen fibrils in the human corneal stroma. The age-related growth of the fibril diameter was mostly a result of an increased number of collagen molecules and, in addition, to some expansion of the intermolecular Bragg spacing probably resulting from glycation-induced cross-linking. The observed expansion of the fibrils in an axial direction may result from reduction of the molecular tilting angle within collagen fibrils. The observed alterations of the collagen framework may have implications for refractive surgery and ocular tonometry achieved through related changes in the biomechanical properties of the cornea.
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              The dynamic sclera: extracellular matrix remodeling in normal ocular growth and myopia development.

              Myopia is a common ocular condition, characterized by excessive elongation of the ocular globe. The prevalence of myopia continues to increase, particularly among highly educated groups, now exceeding 80% in some groups. In parallel with the increased prevalence of myopia, are increases in associated blinding ocular conditions including glaucoma, retinal detachment and macular degeneration, making myopia a significant global health concern. The elongation of the eye is closely related to the biomechanical properties of the sclera, which in turn are largely dependent on the composition of the scleral extracellular matrix. Therefore an understanding of the cellular and extracellular events involved in the regulation of scleral growth and remodeling during childhood and young adulthood will provide future avenues for the treatment of myopia and its associated ocular complications.
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                Author and article information

                Contributors
                rwei@tmu.edu.cn
                Journal
                BMC Ophthalmol
                BMC Ophthalmol
                BMC Ophthalmology
                BioMed Central (London )
                1471-2415
                3 November 2020
                3 November 2020
                2020
                : 20
                : 436
                Affiliations
                [1 ]Tianjin International Joint Research and Development Centre of Ophthalmology and Vision Science, Postal address: 251 Fukang Road, Nankai District, Tianjin, China
                [2 ]GRID grid.412729.b, ISNI 0000 0004 1798 646X, Eye Institute and School of Optometry, , Tianjin Medical University Eye Hospital, ; Postal address: 251 Fukang Road, Nankai District, Tianjin, China
                Author information
                https://orcid.org/0000-0002-9708-0355
                Article
                1704
                10.1186/s12886-020-01704-6
                7607623
                33143686
                bb98fa5a-5f4c-4582-8ac5-e2bf2fe16492
                © The Author(s) 2020

                Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

                History
                : 12 August 2020
                : 23 October 2020
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/501100006606, Natural Science Foundation of Tianjin City;
                Award ID: 81770901
                Categories
                Research Article
                Custom metadata
                © The Author(s) 2020

                Ophthalmology & Optometry
                corvis st,corneal biomechanics,anterior segment parameters,stress-strain index,chinese population

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