scholarly journals Corneal Biomechanical Properties after FS-LASIK with Residual Bed Thickness Less Than 50% of the Original Corneal Thickness

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Haixia Zhang ◽  
Muhammad Ahmad Khan ◽  
Di Zhang ◽  
Xiao Qin ◽  
Ding Lin ◽  
...  
Keyword(s):  
Elastic Moduli ◽  
Corneal Thickness ◽  
Tensile Tests ◽  
Biomechanical Properties ◽  
Uniaxial Tensile ◽  
Stress Region ◽  
Bed Thickness ◽  
Limit Stress ◽  
The Right ◽  
Corneal Biomechanical Properties

Background. The changes in corneal biomechanical properties after LASIK remain an unknown but important topic for surgical design and prognostic evaluation. This study aims to observe the postoperative corneal biomechanical properties one month after LASIK with amount of corneal cutting (ACC) greater than 50% of the central corneal thickness (CCT). Methods. FS-LASIK was performed in 10 left rabbit eyes with ACC being 60% (L60) and 65% (L65) of the CCT, while the right eyes (R) were the control. After 4 weeks, rabbits were executed and corneal strip samples were prepared for uniaxial tensile tests. Results. At the same strain, the stresses of L65 and L60 were larger than those of R. The elastic moduli of L60 and L65 were larger than those of R when the stress was 0.02 MPa, while they began to be less than those of R when stress exceeds the low-stress region. After 10 s relaxation, the stress of specimens L65, L60, and R increased in turn. Conclusion. The elastic moduli of the cornea after FS-LASIK with ACC greater than 50% of the CCT do not become less under normal rabbit IOP. The limit stress grows with the rise of ACC when relaxation becomes stable.

Influence of corneal biomechanical properties on IOP indices in patients with keratoconus

The Eye ◽  
2019 ◽  
Vol 21 (128) ◽  
pp. 15-19
Author(s):  
Irina Bubnova ◽  
Veronica Averich ◽  
Elena Belousova
Keyword(s):  
Disease Progression ◽  
Corneal Thickness ◽  
Central Zone ◽  
Biomechanical Properties ◽  
Resistance Factor ◽  
Corneal Resistance Factor ◽  
Mean Values ◽  
Coefficient Of Elasticity ◽  
D Values ◽  
Corneal Biomechanical Properties

Purpose: Evaluation of corneal biomechanical prop¬erties and their influence on IOP indices in patients with keratoconus. Material and methods. The study included 194 eyes with keratoconus (113 patients aged from 23 to 36 years old). Corneal refraction in central zone varied from 48.25 to 56.75 D, values of corneal thickness ranged from 279 to 558 μm. Patients were divided into 4 groups according to Amsler classification: I stage – 40 eyes; II stage – 78 eyes; III stage – 54 eyes and IV stage – 22 eyes. Standard ophthal¬mological examination was carried out including pneumo¬tonometry. IOP indices and values of biomechanical prop¬erties were evaluated by dynamic bidirectional pneumatic applanation and pneumatic impression. Results. Study of corneal biomechanical properties in patients with keratoconus showed a decrease of such biomechanical indices as corneal hysteresis (CH) on aver¬age to 8.42±1.12 mm Hg, corneal resistance factor (CRF) – to 7.45±0.96 mm Hg, coefficient of elasticity (CE) – 5.35± 0.87 mm Hg. Values of these indices strongly depended on the stage of keratoconus. In the whole sample, the aver¬age corneal compensated IOP (IOPcc) amounted to 15.08± 2.43 mm Hg, Goldman IOP (IOPg) was 11.61±2.37 mm Hg and pneumatic tonometry IOP (IOPp) was 10.13±2.94 mm Hg. IOPcc indices didn’t have any statistically significant differ¬ence in dependence on the stage of keratoconus (р>0.473), while in process of disease progression IOPg and IOPp indi¬ces showed statistically significant decrease of mean values. Conclusion. Progression of keratoconus led to a de¬crease in corneal biomechanical properties which deter¬mine reduction of such indices as IOPg and IOPp in contrast to IOPcc.

scholarly journals The changes of corneal biomechanical properties with long-term treatment of prostaglandin analogue measured by Corvis ST

2020 ◽  
Author(s):  
Na Wu ◽  
Yuhong Chen ◽  
Yaping Yang ◽  
Xinghuai Sun
Keyword(s):  
Open Angle Glaucoma ◽  
Corneal Thickness ◽  
Biomechanical Properties ◽  
Term Treatment ◽  
Prostaglandin Analogue ◽  
Corvis St ◽  
Long Term Treatment ◽  
Corneal Biomechanical Properties

Abstract Background: To investigate the corneal biomechanical changes in primary open angle glaucoma (POAG) patients treated with long-term prostaglandin analogue (PGA). Methods: 111 newly diagnosed POAG patients, including 43 high tension glaucoma (HTG) and 68 normal tension glaucoma (NTG), were measured by Corvis ST to obtain intraocular pressure (IOP), central corneal thickness (CCT) and corneal biomechanical parameters at baseline and at each follow-up visit after initiation of PGA treatment. The follow-up measurements were analyzed by the generalized estimate equation model with an exchangeable correlation structure. Restricted cubic spline was employed to estimate the dose-response relation between follow-up time and corneal biomechanics．Results: The mean follow-up time was 10.3 ± 7.02 months. Deformation amplitude (β=-0.0015, P=0.016), the first applanation velocity (AV1, β=-0.0004, P=0.00058) decreased and the first applanation time (AT1, β=0.0089, P<0.000001) increased statistically significantly with PGA therapy over time after adjusting for age, gender, axial length, corneal curvature, IOP and CCT. In addition, AT1 was lower (7.2950 ± 0.2707 in NTG and 7.5889 ± 0.2873 in HTG, P=0.00011) and AV1 was greater (0.1478 ± 0.0187 in NTG and 0.1314 ± 0.0191 in HTG, P=0.00002) in NTG than in HTG after adjusting for confounding factors.Conclusions: Chronic use of PGA probably influences the corneal biomechanical properties directly, which is to make cornea less deformable. Besides, corneas in NTG tended to be more deformable compared to those in HTG with long-term treatment of PGA.

Evaluation of Biomechanically Corrected Intraocular Pressure Measurements in Keratoconus and Forme Fruste Keratoconus

2020 ◽  
Vol 63 (6) ◽  
pp. 541-549
Author(s):  
Tomoya Nishida ◽  
Takashi Kojima ◽  
Takahiro Kataoka ◽  
Naoki Isogai ◽  
Yoko Yoshida ◽  
...  
Keyword(s):  
Intraocular Pressure ◽  
Biomechanical Properties ◽  
Control Group ◽  
Pressure Measurements ◽  
Altman Plot ◽  
Significant Difference ◽  
The Difference ◽  
The Right ◽  
Corneal Biomechanical Properties ◽  
Forme Fruste Keratoconus

<b><i>Introduction:</i></b> Although biomechanically corrected intraocular pressure (bIOP) is available, the effectiveness of intraocular pressure (IOP) correction in keratoconus and forme fruste keratoconus (FFK) eyes has not been investigated. <b><i>Objective:</i></b> Evaluation of bIOP measurements in eyes with keratoconus and FFK. <b><i>Methods:</i></b> Forty-two eyes in 21 patients with keratoconus in one eye and FFK in the fellow eye were examined (KC/FFK group; mean age 24.62 ± 8.6 years; 16 males and 5 females). The control group consisted of 62 eyes in 31 unaffected subjects (mean age 26.26 ± 3.64 years; 15 males and 16 females). The bIOP was determined using a Scheimpflug-based tonometer (Corvis Scheimpflug Technology [Corvis ST®]) after measuring the IOP with a conventional non-contact tonometer (NIOP). The agreement between NIOP and bIOP values was examined using the Bland-Altman plot. The difference between NIOP and bIOP (bIOP correction amount) was compared between keratoconus and FFK eyes. <b><i>Results:</i></b> In the control group, there were no significant differences between right and left eyes in both NIOP and bIOP values (<i>p</i> = 0.975 and <i>p</i> = 0.224, respectively). In the KC/FFK group, NIOP values were significantly lower in the keratoconus eyes (9.93 ± 1.96 mm Hg) than in the FFK eyes (12.23 ± 3.03 mm Hg; <i>p</i> = 0.0003). There was no significant difference in bIOP values between the right and left eyes of the KC/FFK group (<i>p</i> = 0.168). The bIOP correction amount was significantly increased in keratoconus eyes (3.58 ± 2.12 mm Hg) compared to in FFK eyes (1.80 ± 3.32 mm Hg; <i>p</i> = 0.011). <b><i>Conclusions:</i></b> For eyes with keratoconus and FFK, the bIOP method is effective to adjust IOP measurements based on corneal biomechanical properties.

scholarly journals Role of corneal biomechanical properties in predicting of speed of myopic progression in children wearing orthokeratology lenses or single-vision spectacles

2018 ◽  
Vol 3 (1) ◽  
pp. e000204 ◽  
Author(s):  
Kin Wan ◽  
Sin Wan Cheung ◽  
James S Wolffsohn ◽  
Janis B Orr ◽  
Pauline Cho
Keyword(s):  
Axial Length ◽  
Corneal Thickness ◽  
Significant Negative Correlation ◽  
Biomechanical Properties ◽  
Corneal Hysteresis ◽  
Axial Elongation ◽  
Single Vision ◽  
Length Data ◽  
Corneal Biomechanical Properties

ObjectiveTo determine the characteristics of children who were likely to progress rapidly and gain the greatest benefit from orthokeratology (ortho-k) treatment.Methods and analysisThe files of 113 children who participated in two myopia control studies and wore either ortho-k lenses (n=62) or single-vision spectacles (SVS) (n=51) were reviewed. Baseline cycloplegic subjective refraction, central corneal thickness, axial length, keratometry, intraocular pressure, corneal biomechanical properties and 24-month axial length data were retrieved and analysed.ResultsMultivariate analysis showed that there was significant negative correlation between axial elongation and baseline age and corneal hysteresis (p<0.05) in the SVS group. In the ortho-k group, only baseline age was significantly and negatively associated with axial elongation (p<0.01).ConclusionCorneal biomechanical properties and baseline age can predict the rate of axial elongation in myopic children. It may be beneficial for younger myopic children with low corneal hysteresis to commence ortho-k treatment as early as possible.

scholarly journals Corneal Biomechanical Assessment Using Corneal Visualization Scheimpflug Technology in Keratoconic and Normal Eyes

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Lei Tian ◽  
Yi-Fei Huang ◽  
Li-Qiang Wang ◽  
Hua Bai ◽  
Qun Wang ◽  
...  
Keyword(s):  
Intraocular Pressure ◽  
Corneal Thickness ◽  
Area Under The Curve ◽  
Biomechanical Properties ◽  
Corvis St ◽  
Biomechanical Assessment ◽  
Deformation Amplitude ◽  
Biomechanical Parameters ◽  
And Control ◽  
Corneal Biomechanical Properties

Purpose. To compare the corneal biomechanical properties of keratoconic patients and age-matched controls using corneal visualization Scheimpflug technology (Corvis ST).Methods. Sixty keratoconic eyes from 47 keratoconus patients and 60 normal eyes from 60 controls were enrolled in this prospective study. Tomography and biomechanical parameters of all eyes were obtained with the Pentacam and Corvis ST, respectively. Intraocular pressure was measured using a Goldmann applanation tonometer.Results.The tomography and biomechanical parameters of the keratoconic corneas were significantly different from those of the normal corneas except for the anterior chamber angle, first applanation length, the highest concavity time, and peak distance. The deformation amplitude was the best predictive parameter (area under the curve: 0.882), with a sensitivity of 81.7%, although there was a significant overlap between keratoconic and normal corneas that ranged from 1.0 to 1.4 mm. In both the keratoconus and control groups, the deformation amplitude was negatively correlated with intraocular pressure, central corneal thickness, and corneal volume at 3 and 5 mm.Conclusions. Corvis ST offers an alternative method for measuring corneal biomechanical properties. The possibility of classifying keratoconus based on deformation amplitude deserves clinical attention.

scholarly journals Strain Distribution of Intact Rat Rotator Cuff Tendon-to-Bone Attachments and Attachments With Defects

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Ryan C. Locke ◽  
John M. Peloquin ◽  
Elisabeth A. Lemmon ◽  
Adrianna Szostek ◽  
Dawn M. Elliott ◽  
...  
Keyword(s):  
Area Under The Curve ◽  
Tensile Tests ◽  
Biomechanical Properties ◽  
Defect Group ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Transverse Strain ◽  
Intact Group ◽  
Deformation Patterns ◽  
Insight Into

Abstract This study aimed to experimentally track the tissue-scale strains of the tendon–bone attachment with and without a localized defect. We hypothesized that attachments with a localized defect would develop strain concentrations and would be weaker than intact attachments. Uniaxial tensile tests and digital image correlation were performed on rat infraspinatus tendon-to-bone attachments with defects (defect group) and without defects (intact group). Biomechanical properties were calculated, and tissue-scale strain distributions were quantified for superior and inferior fibrous and calcified regions. At the macroscale, the defect group exhibited reduced stiffness (31.3±3.7 N/mm), reduced ultimate load (24.7±3.8 N), and reduced area under the curve at ultimate stress (3.7±1.5 J/m2) compared to intact attachments (42.4±4.3 N/mm, 39.3±3.7 N, and 5.6±1.4 J/m2, respectively). Transverse strain increased with increasing axial load in the fibrous region of the defect group but did not change for the intact group. Shear strain of the superior fibrous region was significantly higher in the defect group compared to intact group near yield load. This work experimentally identified that attachments may resist failure by distributing strain across the interface and that strain concentrations develop near attachment defects. By establishing the tissue-scale deformation patterns of the attachment, we gained insight into the micromechanical behavior of this interfacial tissue and bolstered our understanding of the deformation mechanisms associated with its ability to resist failure.

Ocular Response Analyser — a New Diagnostic Tool to Measure Corneal Biomechanical Properties and Intraocular Pressure

1970 ◽  
Vol 12 (3) ◽  
pp. 159-168
Author(s):  
Arulmozhi Varman ◽  
Muthuraman Chockalingam
Keyword(s):  
Intraocular Pressure ◽  
Diagnostic Tool ◽  
Pressure Measurement ◽  
Corneal Thickness ◽  
Biomechanical Properties ◽  
Ocular Diseases ◽  
Wide Range ◽  
Corneal Biomechanical Properties ◽  
Ocular Response Analyser

Corneal biomechanical properties have been known to influence the outcome of ocular measurements and procedures for a wide range of ocular diseases. The assessment of corneal biomechanical properties has been a challenge and, for this reason, measurement of the geographical parameters of the cornea, namely corneal thickness and topography, has formed the mainstay of understanding the basis of various ocular pathologies. A newly marketed instrument, the Reichert ocular response analyser has been developed to improve the accuracy of intraocular pressure measurement by uniquely measuring and integrating corneal biomechanical data into its intraocular pressure estimates.

scholarly journals Applications of Scheimpflug Imaging in Glaucoma Management: Current and Potential Applications

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Alexander T. Nguyen ◽  
Tiffany Liu ◽  
Ji Liu
Keyword(s):  
Intraocular Pressure ◽  
Image Reconstruction ◽  
Central Corneal Thickness ◽  
Corneal Thickness ◽  
Anterior Segment ◽  
Three Dimensional ◽  
Biomechanical Properties ◽  
Scheimpflug Imaging ◽  
Potential Applications ◽  
Corneal Biomechanical Properties

Scheimpflug photography is the basis for a variety of imaging devices that are highly versatile. The applications of Scheimpflug imaging are wide in scope, spanning from evaluation of corneal ectasia to quantifying density in nuclear sclerotic cataracts. The potential uses for Scheimpflug-based devices are expanding and a number of them are relevant in glaucoma. In particular, they can provide three-dimensional image reconstruction of the anterior segment which includes assessment of the iridocorneal angle. Photographic analyses allow also for a noncontact method of estimating central corneal thickness (CCT) and intraocular pressure (IOP), as well as the study of various corneal biomechanical properties, which may be useful for stratifying glaucoma risk.

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