An Analytically Solvable Model for Biomechanical Response of the Cornea to Refractive Surgery

2001 ◽  
Vol 123 (5) ◽  
pp. 440-445 ◽  
Author(s):  
Gagik P. Djotyan ◽  
Ron M. Kurtz ◽  
Delia Cabrera Ferna´ndez ◽  
Tibor Juhasz
Keyword(s):  
Intraocular Pressure ◽  
Refractive Surgery ◽  
Solvable Model ◽  
Quantitative Modeling ◽  
Elastic Response ◽  
Ablation Zone ◽  
Biomechanical Response ◽  
Different Types ◽  
Corneal Refractive Surgery ◽  
Best Fit

An analytically solvable model that considers the elasticity of the cornea is developed for use in the current and novel corneal refractive surgery procedures. The model assumes that the cornea is a thin spheroid shell with an elastic response to intraocular pressure. The value of the Young’s modulus of the post-operative cornea and its dependence on the geometric parameters of the ablation zone are estimated employing “best-fit” approach to nomograms currently used in corneal refractive surgery. These elasticity parameters are applied for quantitative modeling of different types of refractive surgery for myopia.

Constitutive Laws for Biomechanical Modeling of Refractive Surgery

1996 ◽  
Vol 118 (4) ◽  
pp. 473-481 ◽  
Author(s):  
Michael R. Bryant ◽  
Peter J. McDonnell
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Refractive Surgery ◽  
Fiber Optic ◽  
Transverse Isotropy ◽  
Constitutive Laws ◽  
Finite Element Models ◽  
Corneal Refractive Surgery ◽  
Best Fit ◽  
Membrane Inflation

Membrane inflation tests were performed on fresh, intact human corneas using a fiber optic displacement probe to measure the apical displacements. Finite element models of each test were used to identify the material properties for four different constitutive laws commonly used to model corneal refractive surgery. Finite element models of radial keratotomy using the different best-fit constitutive laws were then compared. The results suggest that the nonlinearity in the response of the cornea is material rather than geometric, and that material nonlinearity is important for modeling refractive surgery. It was also found that linear transverse isotropy is incapable of representing the anisotropy that has been experimentally measured by others, and that a hyperelastic law is not suitable for modeling the stiffening response of the cornea.

scholarly journals Comparison of intraocular pressure measured by ocular response analyzer and Goldmann applanation tonometer after corneal refractive surgery: a systematic review and meta-analysis

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Hui Zhang ◽  
Zhengtao Sun ◽  
Lin Li ◽  
Ran Sun ◽  
Haixia Zhang
Keyword(s):  
Intraocular Pressure ◽  
Subgroup Analysis ◽  
Refractive Surgery ◽  
Meta Analysis ◽  
Mean Difference ◽  
Ocular Response Analyzer ◽  
Cochrane Library ◽  
Goldmann Applanation Tonometer ◽  
Applanation Tonometer ◽  
Corneal Refractive Surgery

Abstract Background Accurate measurement of intraocular pressure (IOP) after corneal refractive surgery is of great significance to clinic, and comparisons among various IOP measuring instruments are not rare, but there is a lack of unified analysis. Although Goldmann Applanation Tonometer (GAT) is currently the internationally recognized gold standard for IOP measurement, its results are severely affected by central corneal thickness (CCT). Ocular Response Analyzer (ORA) takes certain biomechanical properties of cornea into account and is supposed to be less dependent of CCT. In this study, we conducted the meta-analysis to systematically assess the differences and similarities of IOP values measured by ORA and GAT in patients after corneal refractive surgery from the perspective of evidence-based medicine. Methods The authors searched electronic databases (MEDLINE, EMBASE, Web of science, Cochrane library and Chinese electronic databases of CNKI and Wanfang) from Jan. 2005 to Jan. 2019, studies describing IOP comparisons measured by GAT and ORA after corneal refractive surgery were included. Quality assessment, subgroup analysis, meta-regression analysis and publication bias analysis were applied in succession. Results Among the 273 literatures initially retrieved, 8 literatures (13 groups of data) with a total of 724 eyes were included in the meta-analysis, and all of which were English literatures. In the pooled analysis, the weighted mean difference (WMD) between IOPcc and IOPGAT was 2.67 mmHg (95% CI: 2.20~3.14 mmHg, p < 0.0001), the WMD between IOPg and IOPGAT was − 0.27 mmHg (95% CI: − 0.70~0.16 mmHg, p = 0.2174). In the subgroup analysis of postoperative IOPcc and IOPGAT, the heterogeneity among the data on surgical procedure was zero, while the heterogeneity of other subgroups was still more than 50%. The comparison of the mean difference of pre- and post-operative IOP (∆IOP) was: mean-∆IOPg > mean-∆IOPGAT > mean-∆IOPcc. Conclusions IOPcc, which is less dependent on CCT, may be more close to the true IOP after corneal refractive surgery compared with IOPg and IOPGAT, and the recovery of IOPcc after corneal surface refractive surgery may be more stable than that after lamellar refractive surgery.

Comparison of Intraocular Pressure Correction Programs in Pentacam after Corneal Refractive Surgery

2013 ◽  
Vol 54 (1) ◽  
pp. 26 ◽  
Author(s):  
Lian Hua Hong ◽  
Min Kyu Lee ◽  
Chang Won Park ◽  
Dong Jin Chang ◽  
Ying Jun Li ◽  
...  
Keyword(s):  
Intraocular Pressure ◽  
Refractive Surgery ◽  
Pressure Correction ◽  
Corneal Refractive Surgery

scholarly journals Intraocular Pressure After Corneal Refractive Surgery

2018 ◽  
Vol 72 (3) ◽  
pp. 341
Author(s):  
Valbon Ajazaj ◽  
Gazmend Kacaniku ◽  
Minir Asani ◽  
Afrim Shabani ◽  
Ermal Dida
Keyword(s):  
Intraocular Pressure ◽  
Refractive Surgery ◽  
Corneal Refractive Surgery

scholarly journals Correlation between central corneal thickness and intraocular pressure in various age groups

2010 ◽  
Vol 138 (5-6) ◽  
pp. 279-286 ◽  
Author(s):  
Ivan Marjanovic ◽  
Djordje Kontic ◽  
Paraskeva Hentova-Sencanic ◽  
Vujica Markovic ◽  
Marija Bozic
Keyword(s):  
Intraocular Pressure ◽  
Refractive Surgery ◽  
Central Corneal Thickness ◽  
Corneal Thickness ◽  
Age Groups ◽  
The Third ◽  
Significant Difference ◽  
Applanation Tonometer ◽  
Corneal Refractive Surgery ◽  
Piezoelectric Pressure Sensor

Introduction The Pascal Dynamic Contour Tonometer (DCT) is an ophthalmic investigational device which directly calculates the dynamic pulsatile fluctuations in intraocular pressure (IOP) using a piezoelectric pressure sensor embedded in the devices tip. Objective The aim of this study was to compare IOP results obtained with Goldmann applanation tonometer (GAT), and their correlation with central corneal thickness (CCT) in patients of various age groups. Methods We studied 37 patients (17 male and 20 female), divided into three age groups: younger than 40 years; 40-60 years old, and older than 60 years. In the first and second group there were patients rarely and in the third mostly diagnosed and medicamentously compensated glaucoma. In topical anesthesia, first we measured CCT, with ultrasound pachimeter, then IOP with DCT and GAT. Results Statistically significant difference between measurements of IOP with the DCT and GAT appeared in all groups: I mean diff. -1.71?}1.27 mm; p<0.0001; II mean diff. -1.19?}1.06 mm; p<0.0001; III mean diff. -1.69?}1.67 mm; p<0.0001. CCT was in indirect correlation with the values of IOP measured both with the DCT and GAT in the first and third, while it was in the direct correlation with these values in the second group. Conclusion CCT had no influence on IOP measurements both with the DCT and GAT in none of the groups. The DCT cannot replace GAT, but it is a reliable device for the measurement of IOP particularly in corneal deformations (keratoconus, after corneal refractive surgery, corneal scars, etc.). .

scholarly journals Comparison of intraocular pressure measured by ocular response analyzer and Goldmann applanation tonometer after corneal refractive surgery: a systematic review and meta-analysis

2019 ◽  
Author(s):  
Hui Zhang ◽  
Zhengtao Sun ◽  
Lin Li ◽  
Ran Sun ◽  
Haixia Zhang
Keyword(s):  
Intraocular Pressure ◽  
Subgroup Analysis ◽  
Refractive Surgery ◽  
Meta Analysis ◽  
Ocular Response Analyzer ◽  
Cochrane Library ◽  
Measuring Instruments ◽  
Goldmann Applanation Tonometer ◽  
Applanation Tonometer ◽  
Corneal Refractive Surgery

Abstract Background: Accurate measurement of intraocular pressure (IOP) after corneal refractive surgery is of great significance to clinic, and comparisons among various IOP measuring instruments are not rare, but there is a lack of unified analysis. GAT is currently the internationally recognized gold standard for IOP measurement, while ORA is said to take into account the biomechanical properties of cornea. In this study, we conducted this meta-analysis to systematically assess the differences and similarities of IOP values measured by ORA and GAT in patients after corneal refractive surgery from the perspective of evidence-based medicine. Methods: The authors searched electronic databases (MEDLINE, EMBASE, Web of science, Cochrane library and Chinese electronic databases of CNKI and Wanfang) from Jan 2005 to Jan 2019, studies describing IOP comparisons measured by GAT and ORA after corneal refractive surgery were included. Quality assessment, subgroup analysis, meta-regression analysis and publication bias analysis were applied in succession. Results: Among the 273 literatures initially retrieved, 8 literatures (13 groups of data) with a total of 724 eyes were included in the meta-analysis, and all of which were English literatures. In the pooled analysis, the weighted mean difference (WMD) between IOPcc and IOPGAT was 2.67 mmHg (95% CI: 2.20~3.14 mmHg, p < 0.0001), the WMD between IOPg and IOPGAT was -0.27 mmHg (95% CI: -0.70~0.16 mmHg, p = 0.2174). In the subgroup analysis of postoperative IOPcc and IOPGAT, the heterogeneity among the data on surgical procedure was zero, while the heterogeneity of other subgroups was still more than 50%. The comparison of mean-∆IOP is: mean-∆IOPg > mean-∆IOPGAT > mean-∆IOPcc. Conclusions: IOPcc may be more close to the true IOP after corneal refractive surgery compared with IOPg and IOPGAT, and the recovery of IOPcc after corneal surface refractive surgery may be more stable than that after lamellar refractive surgery. Keywords: corneal refractive surgery; intraocular pressure; ocular response analyzer; Goldmann applanation tonometer; meta-analysis;

An Analysis on the Change Rule of Eyeball's Biological Parameters of Different Types in the Refraction State and Vision Before and After Refraction

2018 ◽  
Vol 8 (9) ◽  
pp. 1881-1885
Author(s):  
Jiang Yingmei ◽  
Jin Tao ◽  
Yang Xueqi ◽  
Dai Xiaoli ◽  
Jin Ri ◽  
...  
Keyword(s):  
Refractive Surgery ◽  
Operation Mode ◽  
Frontal Surface ◽  
Surface Appearance ◽  
Lens Thickness ◽  
Refractive Power ◽  
Different Types ◽  
Before And After ◽  
Corneal Refractive Surgery

The ametropia is the most widespread eye disease for the humans. Wherein, the myopia is the commonest ophthalmological reason influencing the distant vision. The excimer laser corneal refractive surgery has always been an operation mode most widely used in myopic correction operations for a number of years. The laser assisted in-situ keratomi (LASIK) mainly transforms the frontal surface appearance of the cornea to change the corneal refraction power, and its correction effect is influenced by a great many factors such as regression and hydration of cornea. Thus, a lot of surgeons would combine own experience in conducting LASIK myopic correction. The myopic regression would affect the foreseeability, operation effect and stability of corneal refractive surgery, which results in reduction of the patients' visual quality in turn. The pathogenesis still needs further study. The change of lens thickness does not only lead to change in depth of central anterior chamber, but also would cause the change in refractive power of lens, thereby influencing the whole dioptric system of the eyeball. The previous research on postoperative regression was mostly focused on the corneal refraction, while few efforts were put in the changes of lens thickness and refractive power after LASIK.

scholarly journals Comparison of intraocular pressure measured by ocular response analyzer and Goldmann applanation tonometer after corneal refractive surgery: a systematic review and meta-analysis

2019 ◽  
Author(s):  
Hui Zhang ◽  
Zhengtao Sun ◽  
Lin Li ◽  
Ran Sun ◽  
Haixia Zhang
Keyword(s):  
Intraocular Pressure ◽  
Subgroup Analysis ◽  
Refractive Surgery ◽  
Meta Analysis ◽  
Mean Difference ◽  
Ocular Response Analyzer ◽  
Cochrane Library ◽  
Goldmann Applanation Tonometer ◽  
Applanation Tonometer ◽  
Corneal Refractive Surgery

Abstract Background: Accurate measurement of intraocular pressure (IOP) after corneal refractive surgery is of great significance to clinic, and comparisons among various IOP measuring instruments are not rare, but there is a lack of unified analysis. Although Goldmann Applanation Tonometer (GAT) is currently the internationally recognized gold standard for IOP measurement, its results are severely affected by central corneal thickness (CCT). Ocular Response Analyzer (ORA) takes certain biomechanical properties of cornea into account and is supposed to be less dependent of CCT. In this study, we conducted the meta-analysis to systematically assess the differences and similarities of IOP values measured by ORA and GAT in patients after corneal refractive surgery from the perspective of evidence-based medicine. Methods: The authors searched electronic databases (MEDLINE, EMBASE, Web of science, Cochrane library and Chinese electronic databases of CNKI and Wanfang) from Jan. 2005 to Jan. 2019, studies describing IOP comparisons measured by GAT and ORA after corneal refractive surgery were included. Quality assessment, subgroup analysis, meta-regression analysis and publication bias analysis were applied in succession. Results: Among the 273 literatures initially retrieved, 8 literatures (13 groups of data) with a total of 724 eyes were included in the meta-analysis, and all of which were English literatures. In the pooled analysis, the weighted mean difference (WMD) between IOPcc and IOPGAT was 2.67 mmHg (95% CI: 2.20~3.14 mmHg, p < 0.0001), the WMD between IOPg and IOPGAT was -0.27 mmHg (95% CI: -0.70~0.16 mmHg, p = 0.2174). In the subgroup analysis of postoperative IOPcc and IOPGAT, the heterogeneity among the data on surgical procedure was zero, while the heterogeneity of other subgroups was still more than 50%. The comparison of the mean difference of pre- and post-operative IOP (∆IOP) was: mean-∆IOPg > mean-∆IOPGAT > mean-∆IOPcc. Conclusions: IOPcc, which is less dependent on CCT, may be more close to the true IOP after corneal refractive surgery compared with IOPg and IOPGAT, and the recovery of IOPcc after corneal surface refractive surgery may be more stable than that after lamellar refractive surgery.

Sign in / Sign up

Export Citation Format

Share Document