Evaluation of Corneal Biomechanical Changes After Collagen Crosslinking in Patients with Progressive Keratoconus by Ocular Response Analyzer

Küçümen, Raciha Beril; Şahan, Berna; Yildirim, Canan Aslı Utine; Çiftçi, Faruk

doi:10.4274/tjo.56750

Cited by 10 publications

(7 citation statements)

References 32 publications

(37 reference statements)

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“… 36 , 37 In another study evaluating biomechanical changes with ORA before and after CXL, p2area, which is the most valuable predictive parameter in progression, was reported to be the parameter that best demonstrates biomechanical changes after CXL, but there was no significant change in CRF and CH values. 38 In a study by Küçümen et al 39 examining changes in CRF and CH after CXL, no statistically significant change was observed in CH in the early or late postoperative period, while the change in CRF showed early significance that disappeared in the late postoperative period.…”

Section: Discussionmentioning

confidence: 97%

Superiority of Baseline Biomechanical Properties over Corneal Tomography in Predicting Keratoconus Progression

Erol¹,

Atalay²,

Özalp³

et al. 2021

tjo

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Objectives: To determine corneal biomechanical and tomographic factors associated with keratoconus (KC) progression. Materials and Methods: This study included 111 eyes of 111 KC patients who were followed-up for at least 1 year. Progression was defined as the presence of progressive change between the first two consecutive baseline visits in any single parameter (A, B, or C) ≥95% confidence interval or two parameters ≥80% confidence interval for the KC population evaluated by the Belin ABCD progression display. The eye with better initial tomographic findings was chosen as the study eye. Analyzed Pentacam parameters were maximum keratometry (Kmax), minimum pachymetry (Kmin), central corneal thickness, thinnest corneal thickness, 90° vertical anterior and posterior coma data in Zernike analysis, and Belin Ambrosio Enhanced Ectasia Display Final D value. Corneal hysteresis (CH) and corneal resistance factor (CRF) were analyzed together with the waveform parameters obtained with Ocular Response Analyzer (ORA). Factors related to KC progression were evaluated using t-tests and logistic regression tests. Statistical significance was accepted as p<0.05. Results: There were 44 (mean age: 27.1±8.5 years, female: 25) and 67 (mean age: 31.1±9.1 years, female: 36) patients in the progressive and non-progressive groups, respectively. Although Pentacam parameters along with CH and CRF were similar between the two groups, ORA waveform parameter derived from the second applanation signal p2area was statistically significantly lower in the progressive group (p=0.02). Each 100-unit decrease in p2area increased the likelihood of keratoconus progression by approximately 30% in the logistic regression analysis (β=0.707, p=0.001, model r2=0.27). Conclusion: Parameters derived from the second applanation signal of ORA may be superior to conventional ORA parameters and corneal tomography in predicting KC progression.

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Section: Discussionmentioning

confidence: 97%

Superiority of Baseline Biomechanical Properties over Corneal Tomography in Predicting Keratoconus Progression

Erol¹,

Atalay²,

Özalp³

et al. 2021

tjo

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“…Another limitation of this study is that when we simulate ORA measurements, we calculated CH and CRF according to Eq (5) and (6), which may be not the real relation of ORA parameters and P 1 , P 2 . While the relationship has not been determined at present, researches have reported that experimental CH and CRF are linear positive correlation with the calculated CH and CRF [29] and our aim was to find the correlation between ORA parameters and corneal biomechanical parameters qualitatively. Therefore, it is feasible to calculate CH and CRF by Eq (5) and (6).…”

Section: Discussionmentioning

confidence: 98%

“…As corneal topography is measured at a specific intraocular pressure IOP and is distinct from the unloaded shape that would be obtained at an IOP of 0 mm Hg, the undeformed state was solved by a custom finite element model at first. The variation of central corneal coordinate along the air-puff force during the measurements was extracted (Figure 3(b)) to get the two applanation pressures ( P 1 and P 2 ) and ORA parameters (CH and CRF) were calculated according to the following equations [29]:T17CH=P1−P2CRF=P1−0.7P2…”

Section: Methodsmentioning

confidence: 99%

The Mechanical Interpretation of Ocular Response Analyzer Parameters

Xiao

Zhang

et al. 2019

BioMed Research International

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Purpose. Ocular Response Analyzer (ORA) is one of the most widely used devices in clinic, while the mechanical interpretations of parameters obtained from ORA have not been understood completely. The aim of this research is to explore the mechanical interpretation of ORA parameters. Methods. Rabbits aged 3-24 months were measured with ORA in vivo and corneal strips uniaxial tensile tests to get ORA parameters and corneal biomechanical parameters (corneal elastic modulus, relaxation time, and relaxation limit). The mechanical interpretation of ORA parameters was cognized preliminarily by analyzing the correlation between ORA parameters and corneal biomechanical parameters. On the other hand, finite element method was applied to simulate ORA measurements with different corneal biomechanical parameters to obtain quantitative relationship between ORA parameters and corneal biomechanical parameters further. Results. Biomechanical experimental results showed that Corneal Resistance Factor (CRF) was correlated with corneal elastic modulus and relaxation limit significantly, while the significant correlations between Corneal Hysteresis (CH) and corneal biomechanical parameters were not observed. Results of finite element analysis showed that both CH and CRF were correlated with corneal elastic modulus, relaxation limit, and relaxation time significantly. Besides, corneal elastic modulus was positively correlated with upslop1 and upslop2 and negatively correlated with w2. Conclusions. For all ORA parameters, CH, CRF, the upslope, and the width of the peaks are parameters which may reflect corneal elastic properties. It is viable to cognize mechanical interpretation of ORA parameters by the comparisons of the data from ORA and biomechanical tests of rabbits with different ages and the simulations of ORA based on finite element methods. Further studies are needed to confirm the mechanical interpretation.

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“…B12) and the UVA undergo a photochemical reaction with environmental oxygen and generate free oxygen radicals. This reaction is responsible for the formation of additional covalent bonds between the collagen fibrils in the stroma with the result of reinforcing the structure of corneal stroma influencing its biomechanical function [19]. The literature reports few data about the possible modification of mechanical behaviour of corneal tissue due the induced injury and also due to the treatment of the lesion with the riboflavin/UV-A corneal phototherapy.…”

Section: Introductionmentioning

confidence: 99%

Mechanical behaviour of healthy versus alkali-lesioned corneas by a porcine organ culture model

et al. 2021

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Background Cornea is a composite tissue exhibiting nonlinear and time-dependent mechanical properties. Corneal ulcers are one of the main pathologies that affect this tissue, disrupting its structural integrity and leading to impaired functions. In this study, uniaxial tensile and stress-relaxation tests are developed to evaluate stress-strain and time-dependent mechanical behaviour of porcine corneas. Results The samples are split in two groups: some corneas are analysed in an unaltered state (healthy samples), while others are injured with alkaline solution to create an experimental ulcer (lesioned samples). Furthermore, within each group, corneas are examined in two conditions: few hours after the enucleation (fresh samples) or after 7 days in a specific culture medium for the tissue (cultured samples). Finally, another condition is added: corneas from all the groups undergo or not a cross-linking treatment. In both stress-strain and stress-relaxation tests, a weakening of the tissue is observed due to the imposed conditions (lesion, culture and treatment), represented by a lower stiffness and increased stress-relaxation. Conclusions Alkali-induced corneal stromal melting determines changes in the mechanical response that can be related to a damage at microstructural level. The results of the present study represent the basis for the investigation of traditional and innovative corneal therapies.

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Evaluation of Corneal Biomechanical Changes After Collagen Crosslinking in Patients with Progressive Keratoconus by Ocular Response Analyzer

Cited by 10 publications

References 32 publications

Superiority of Baseline Biomechanical Properties over Corneal Tomography in Predicting Keratoconus Progression

Superiority of Baseline Biomechanical Properties over Corneal Tomography in Predicting Keratoconus Progression

The Mechanical Interpretation of Ocular Response Analyzer Parameters

Mechanical behaviour of healthy versus alkali-lesioned corneas by a porcine organ culture model

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