ABSTRACT
Corneal visualization Scheimpflug technology(Corvis ST)is currently the most commonly used clinical device for assessing in vivo corneal biomechanics. The new parameter stress-strain index(SSI)has been a hot topic of clinical research in recent years, which not only directly reflect corneal biomaterial stiffness, but also closely correlates with the progression of certain diseases. SSI was generated based on the predictions of corneal behavior using finite element(FE)numerical modeling to simulate the effects of intraocular pressure and Corvis ST jets. The SSI algorithm does not change with central corneal thickness(CCT), intraocular pressure, or biomechanically corrected intraocular pressure(BIOP), but it is clearly associated with altered collagen fibres in the corneosclera. The principles of SSI, the relationship between age and SSI, the relationship between axial length and SSI, the relationship between myopia and SSI, and the application of SSI are summarized and concluded.
ABSTRACT
AIM: To study the characteristics of new corneal biomechanical parameters in different degrees of myopia and analyze the correlation of the new parameter stress-strain index(SSI).METHODS: A cross-sectional study was conducted on 366 adult patients(718 eyes)with different degrees of myopia who received treatment at the First Affiliated Hospital of Dali University from October 2021 to November 2021, aged 18-50 years, and the spherical equivalent(SE)was -0.50～-16.75D. The axial length(AL)of the eye was measured by IOL master, and the new corneal biomechanical parameters, central corneal thickness(CCT)and intraocular pressure(IOP)were measured by corneal visualization Scheimpflug technology(Corvis ST). The subjects were categorized into low myopia, moderate myopia and high myopia groups according to SE. The data were analyzed by ANOVA and Pearson correlation.RESULTS: The ratio of the thinnest corneal thickness to horizontal thickness change rate(ARTh)and SSI were statistically significant(P<0.001), while the remaining parameters were not statistically significant(P>0.05). SSI was positively correlated with age(r=0.102, P=0.006), SE(r=0.361, P<0.001), IOP(r=0.175, P<0.001), CCT(r=0.098, P=0.009), SPA1(r=0.182, P<0.001), negatively correlated with AL(r=-0.331, P<0.001), IR(r=-0.545, P<0.001)and had no correlation with other corneal biomechanical parameters(P>0.05).CONCLUSION: With the increase of myopia degree and the elongation of the axial length, the SSI value becomes smaller and the corneal hardness decreases. SSI may be a helpful corneal biomechanical indicator for future research on myopia.
ABSTRACT
AIM:To evaluate the changes in corneal biomechanics of patients with moderate refractive error after receiving small-incision lenticule extraction(SMILE)and femtosecond laser-assisted laser in situ keratomileusis(FS-LASIK)using the corneal visualization Scheimpflug technology(Corvis ST).METHODS:Prospective cohort study. A total of 65 moderate myopia patients(65 eyes)who were scheduled to undergo refractive surgery at the Ophthalmic Refractive Surgery Center of the Ningxia Eye Hospital from November 2020 to November 2021 were included in the study, and there were 30 eyes in the SMILE group and 35 eyes in the FS-LASIK group. The changes in corneal biomechanical parameters, including integrated radius(IR), inverse concave radius(ICR), deformation amplitude ratio 2mm(DAR2), stiffness parameter at first applanation(SP-A1), ambrosio relational thickness(ARTh)and the central curvature radius at highest concavity(HC-Radius)were observed by Corvis ST between both groups preoperatively and 1 and 3mo postoperatively.RESULTS: There were no statistical significance in biomechanical parameters between two groups of patients 1 and 3mo postoperatively(P>0.05). IR, ICR and DAR2 of each groups of patients 1 and 3mo postoperatively were significantly increased than those preoperatively, and SP-A1, ARTh and HC-Radius were significantly decreased than those preoperatively(all P<0.05). The biomechanical parameters at 1mo and 3mo postoperatively showed no statistical significance(P>0.05). In addition, a positive correlation was found between central corneal thickness(CCT)and ARTh and SP-A1 of the two groups of patients at 3mo postoperatively(FS-LASIK group: r=0.727, 0.819, SMLIE group: r=0.683, 0.434, all P<0.05), while a negative correlation was found between CCT and IR and ICR at 3mo postoperatively.(FS-LASIK group: r=-0.697, -0.622, SMLIE group: r=-0.447, -0.491, all P<0.05).CONCLUSION:For patients with moderate myopia, both SMILE and FS-LASIK can reduce corneal biomechanical stability. Both surgeries showed no significant differences in the effect on biomechanical, and the biomechanical has been stabilized at 1mo postoperatively. A correlation was found between postoperative CCT and ARTh, SP-A1, IR and ICR.
ABSTRACT
AIM:To investigate the correlation between corneal biomechanical parameters measured by the corneal visualization Scheimpflug Technology(Corvis ST)and corneal high-order aberrations(HOAs)in children with mild to moderate myopia.METHODS:A cross-sectional study. A total of 255 pediatric patients with myopia enrolled from April to July 2021 in Tianjin Medical University Eye Hospital were continuously collected, and all the right eyes were taken for analysis. Corneal biomechanical parameters were obtained from Corvis ST. Pentacam three-dimensional anterior segment analyzer was used to measure total corneal higher-order aberrations(RMSh), third order aberrations(RMS3)and fourth order aberrations(RMS4).RESULTS:RMS3 was positively correlated with the second applanation time(A2T)(r=0.175, P=0.009)and negatively correlated with the axis length(AL)(r=-0.155, P=0.014). RMS4 was negatively correlated with the highest concavity radius(HCR)(r=-0.165, P=0.009). RMSh was negatively correlated with HCR and AL(r=-0.152, P=0.037; r=-0.175, P=0.005).CONCLUSION:There is a correlation between corneal biomechanical parameters and HOAs in children with myopia. Cornea with higher stiffness and stronger deformation resistance has smaller RMS3, RMS4 and RMSh.
ABSTRACT
@#AIM: To investigate the corneal biomechanical parameters alteration after phacoemulsitication with 2.4mm corneal incision within 1mo by Corvist ST.<p>METHODS: A self control study was performed. Twenty-eight age related cataract patients(56 eyes), who were in accordance with the inclusion criteria, received phacoemulsification with 2.4mm corneal incision from March to September in 2019. Corneal biomechanical parameters were measured preoperatively and postoperatively on 3d, 6d and 30d by Corvis ST.<p>RESULTS: The first applanation length(A1L), the second applanation time(A2T)and corneal thickness(CCT)were significantly different between preoperation and postoperation(<i>F</i>=10.534, 11.655, 14.734; all <i>P</i><0.05). The value of A1L on 3d postoperative was significantly increased than that on the day before operation, 6d and 30d postoperative, while the A2T value was significantly reduced(<i>P</i><0.05). But there was no different in A2L and A2T between preoperation and 6d postoperative(<i>P</i>>0.05). The value of central corneal thickness(CCT)was significantly increased on 3d and 6d postoperative compared with the preoperative parameter(<i>P</i><0.05). The value of CCT got the maximum value on the 3d after surgery, and recovered to the preoperative level on the 30d after surgery. <p>CONCLUSION: Phacoemulsitication with 2.4mm corneal incision change the corneal biomechanical preoperties. The corneal biomechanical parameters are basically recovered in the 30d postoperative.
ABSTRACT
Objective To study the changes in biomechanical properties of human cornea after laser in situ keratomileusis (LASIK) and predict corneal stiffness after the LASIK surgery. Methods According to the measurement results from corneal visualization scheimpflug technology (Corvis ST), the corneal tangent stiffness coefficient (STSC) and energy absorbed area (Aabsorbed) were calculated. The change patterns of corneal stiffness and viscosity after refractive surgery were analyzed. Results The difference of corneal STSC and Aabsorbed before and after LASIK had a statistical significance (P<0.05). The obtained formula for predicting corneal stiffness after refractive surgery was: Sbefore surgery =1.055bIOPbefore surgery + 0.015CCTbefore surgery，Safter surgery =0.937Sbefore surgery +0.019CCTafter surgery. Conclusions LASIK surgery not only changes corneal thickness, but also reduces corneal stiffness and viscosity. Prediction of corneal stiffness after surgery can provide guidance for the design of clinical surgery and improve the safety of surgery.
ABSTRACT
Study of the mechanical properties of in vivo corneal materials is an important basis for further study of corneal physiological and pathological phenomena by means of finite element method. In this paper, the elastic coefficient ( ) and viscous coefficient ( ) of normal cornea and keratoconus under pulse pressure are calculated by using standard linear solid model with the data provided by corneal visualization scheimpflug technology. The results showed that there was a significant difference of and between normal cornea and keratoconus cornea ( < 0.05). Receiver operating characteristic curve analysis showed that the area under curve (AUC) for , and their combined indicators were 0.776, 0.895 and 0.948, respectively, which indicated that keratoconus could be predicted by and . The results of this study may provide a reference for the early diagnosis of keratoconus and avoid the occurrence of keratoconus after operation, so it has a certain clinical value.
Subject(s)
Humans , Area Under Curve , Cornea , Physiology , Elasticity , Keratoconus , Pathology , ROC Curve , ViscosityABSTRACT
Objective To study the sensitivity and specificity of parameter Corvis biomechanical index (CBI)— a new biomechanical index of Corvis ST in the diagnosis of keratoconus and evaluate the role of CBI in the diagnosis of keratoconus and the change of biomechanic.Methods A diagnostic trial study was adopted,and 66 eyes from 49 keratoconic patients (keratoconus group) and 91 right eyes from 91 myopic patients (control group) from April in 2018 to August in 2018 in Henan Eye Hospital were enrolled.Pentacam and Corvis ST examinations were performed by the same operator after the basic eye examinations.Using the evaluation of diagnostic test,consistency test,and receiver operating characteristic (ROC) curve analysis,gain the outcome of the sensitivity,specificity,consistency,Youden index,and area under the ROC curve of the parameter CBI.This study protocol was approved by Ethic Committee of Henan Eye Hospital and followed the Declaration of Helsinki.Written informed consent was obtained from each patient prior to any medical examination.Results Sixty eyes were diagnosed as keratoconus by the parameter CBI of Corvis ST.Evaluation of diagnosis test:the sensitivity was 97.0％,and the specificity was 97.8％;consistency check:Kappa =0.948,P＜0.05.ROC curve analysis:the sensitivity was 98.5％,the specificity was 96.8％,Youden index was 96.3％,P＜0.000 1 and AUC was 0.996.Conclusions CBI can separate healthy eyes from keratoconic eyes with highly sensitivity and specificity,which was highly consistency with results of Rabinowitz keratoconus diagnostic criteria.CBI could be used as a new biomechanical indicator for the diagnosis of keratoconus.
ABSTRACT
Glaucoma is one of the leading causes of blindness worldwide.Various factors are related to the development and progression of glaucoma.High intraocular pressure is an important risk factor.In recent years,many studies have focused on other potential risk factors for glaucoma,such as intraocular pressure-independent factors,including vascular factors,central corneal thickness,etc.The relationship between corneal biomechanical parameters and glaucoma has been attracting more and more attentions.The corneal biomechanics measurement instruments include ocular response analyzer (ORA) and corneal visualization scheimpflug technology (Corvis-ST),which are all commonly used in clinical practice.Some studies showed that the corneas in glaucoma patients were more easily to deform.Corneal biomechanical characteristics may reflect the anatomic structure weakness of the eyeball.For example,more easily deforming of cornea results in smaller tolerance of sclera and lamina cribros to intraocular pressure,which makes the optic disc more vulnerable.This may be one of the causes of glaucomatous optic nerve damage.Corneal biomechanical parameters have a certain extent relationship with the severity of glaucoma.In order to probe into the pathogenesis of glaucoma deeply,we reviewed corneal biomechanics characteristics,application of corneal biomechanical properties measuring instruments in clinical practice and the relationships between corneal biomechanics characteristics and the development and progression of glaucoma,as well as the therapeutic effectiveness of glaucoma.
ABSTRACT
As a new biomechanical measuring instrument,corneal visualization Scheimpflug technology (Corvis ST) integrates ultra-high speed Scheimpflug technology into non-contact intraocular pressure measuring instrument.Corvis ST can dynamically record and analyze the corneal pressure form change and the biomechanical change during the morphological reduction process.With a large number of basic research and a long time accumulation of clinical data,The application of Corvis ST in ophthalmology was gradually carried out.This paper introduced the biomechanical properties of the cornea and the application of corneal biomechanical measuring instrument in ophthalmology,thereby providing a reference for related research.
ABSTRACT
Objective To explore the corneal biomechanical characteristics change in cataractous eyes before and after phacoemulsification using corneal visualization Scheimpflug technology (Corvis ST) and evaluate the influence of 3 mm clear corneal incision on corneal biomechanics.Methods A self-control study was performed.Thirty-six eyes of 36 patients who received phacoemulsification were enrolled in Tianjin Eye Hospital from March to May 2015.The first/second applanation time,the first/second applanation length,the first/second applanation velocity,the highest concavity time,the highest concavity radius,peak distance (PD),deformation amplitude (DA),intraocular pressure,corrected intraocular pressure and central corneal thickness(CCT) were measured in preoperation,postoperative 1 week and postoperative 1 month.This study protocal was approved by Ethic Committee of Tianjin Eye Hospital,and written informed consent was obtained from each patient prior to any medical examination.Results The first/second applanation length,intraocular pressure,corrected intraocular pressure,PD,DA and CCT were significantly different among preoperation,postoperative 1 week and postoperative 1 month (F =3.42,5.24,4.21,3.82,3.91,4.03,3.62;all at P＜0.05).Compared with the preoperative parameters,the first applanation length value was increased,and the second applanation length was reduced;the intraocular pressure and corrected intraocular pressure were elevated,and PD and DA values were increased,and the CCT was thicked in 1 week postoperative,with significant differences between the two time points (all at P＜0.05).Compared with the postoperative 1 week,the first applanation length value was reduced,and the second applanation length value was increased;the intraocular pressure and corrected intraocular pressure were lowed,and PD and DA values were smaller,and the CCT was thinner in postoperative 1 month,showing significant differences between the two time points (all at P ＜ 0.05).The first applanation length,the second applanation length,the intraocular pressure,corrected intraocular pressure,PD,DA and CCT in postoperative 1 month returned to the preoperative levels (all at P ＞ 0.05).Conclusions Corneal biomechanical properties occur change in the early stage after phacoemulsification and return to normal in postoperative 1 month.
ABSTRACT
Objective To compare the corneal biomechanical properties between keratoconic eyes and normal eyes by using corneal visualization Scheimpflug technology (Corvis ST),and to evaluate the diagnostic value of corneal biomechanical parameters based on Corvis ST in keratoconus.Methods A prospective cases-control study was performed.Twenty-four keratoconic eyes from 17 patients and 40 normal eyes (right eye) from 40 participants were enrolled from October to December in Peking University First Hospital.Anterior segment parameters and refractive diopters were obtained with Topography (TMS-4) and mydriatic refraction.Biomechanical parameters were assessed with Corvis ST.Independent sample t-test and Wilcoxon rank sum test were used to compare the parameters of the two groups.The receiver operating characteristic (ROC) curves were plotted to distinguish keratoconus from the normal cornea.Diagnostic efficacies of all parameters were analyzed and some parameters were used as independent variables to establish a Logistic regression model.Results Maximum deformation amplitude of highest concavity (HCDA),maximum corneal velocity during the second applanation (Vout) and distance between both non-deformed peaks (PD) in the keratoconus group were higher than those in the normal control group,and first applanation time (A1T),cord length of first applanation (ALL),cord length of second applanation (A2L),radius value of central concave curvature at highest concavity (HCR) were lower than those in the normal control group,with significant differences between the two groups (all at P＜0.05).Maximum corneal velocity during the first applanation (Vin),second applanation time (A2T) and time taken to reach highest concavity (HCT) were insignificantly different between the two groups (all at P＞0.05).Many parameters had diagnostic values in keratoconus assessed by ROC analysis.HCR was the most efficient parameter showed by ROC evaluation (area under the curve was 0.927,sensitivity was 95.8％,specificity was 82.5％).The Logistic model were established with two independent variables,HCR (OR=0.205) and central corneal thickness (CCT) (OR=0.970).The forecast model of keratoconus diagnosis was established as follows:Logistic (P) =23.47-1.59×HCR-0.30×CCT.Diagnostic sensitivity and specificity were enhanced by using this model,the sensitivity was 95.8％,and the specificity was 95.0％.Conclnsions It is useful to evaluate the corneal biomechanical properties with Corvis ST.HCR is an efficient auxiliary testing index of diagnosis or screening of keratoconus.
ABSTRACT
AIM:To explore the corneal biomechanical properties of the elderly with different axial length ( AL) and corneal curvature by corneal visualization Scheimpflug Technology ( Corvis ST) .?METHODS: Cross - sectional study. A total of 161 patients ( 297 eyes ) undergoing phacoemulsification were collected in this study. They were divided into 22-24mm, 24-26mm, more than 26mm groups according to axial length ( 190 eyes, 54 eyes and 53 eyes, respectively). Those of whom axial length was 22-24mm and the corneal curvature was 42-44D were divided into male and female groups ( 44 eyes and 49 eyes, respectively). Those of whom axial length was 22-24mm were divided into 42-44D group, more than 44D group according to corneal curvature ( 88 eyes, 102 eyes, respectively ) . Corvis ST was used to measure the biomechanical parameters of the cornea. The differences in the parameters between different groups were analyzed using the independent-samples t test or one-way analysis of variance and correlation analyses were performed using Pearson correlation analysis.?RESULTS:When comparing the corneal biomechanical parameters, no statistically significant differences were found between male and female groups (P>0. 05). The first applanation length and second applanation length among different corneal curvatures were statistically significant (P<0. 05). There was statistical significance on the difference of the second applanation velocity, deformation amplitude, central cornea thickness, intraocular pressure in different AL groups (P<0. 05). The axial length was positively correlated with deformation amplitude, intraocular pressure ( r=0. 429, 0. 278; P < 0. 001 ), but there was negative linear correlation between the patient's axial length and central cornea thickness, the second applanation velocity ( r=-0. 291, -0. 415;P<0. 001).?CONCLUSION: The corneal curvature and ocular axial length may be the factors affecting the corneal biomechanical characteristics. The longer axial length, the thinner corneal thickness, the more easily the corneal is deformed, and with the increase of the axial length, intraocular pressure also increases.
ABSTRACT
Background Keratoconus is a chronic and progressive non-inflammatory ectatic disorder characterized by corneal thinning and irregular corneal topography,and its pathgenesis is a hot topic.A suitable animal model of keratoconus is still lacking,which limits the progress of relevant research.Corneal ectasia is a main anatomical basis of keratoconus,so we assume that keratoconus model could be constructed by simulating corneal ectasia.Objective This study was to investigate the influence of collagenase type Ⅱ on biomechanical responses detected by corneal visualization Scheimpflug technology (Corvis ST) and the feasibility of construction of rabbit model of corneal ectasia using coliagenase type Ⅱ.Methods This study protocol was approved by Ethic Committee of Peking University First Hospital and followed the Statement about experimental animal use and care from Association for Research in Vision and Ophthalmology (ARVO).Keratectasia models were established in 10 right eyes of 10 New Zealand white rabbits by soaking 8 mm-diameter central cornea using collagenase type Ⅱ solution prepared by PBS solution containing 15％ dextran (200 μl of 5 mg/ml) for 30 minutes after epithelial debridement,and only 200 μl PBS solution containing 15％ dextran was used in the same way in the left eyes as controls.The average corneal curvature (Km) and central corneal thickness (CCT) were measured with hand-held electronic corneal curvature meter and corneal ultra-sonic pachymetry respectively before modeling and 14 days after modeling.Corneal biomechanical parameters and intraocular pressure were measured in vivo by using Corvis ST at day 14 after modeling.The rabbits were sacrificed at day 14 after modeling,and corneal sections were prepared for hematoxylineosin staining and transmission electron microscopic examination.Results There were no significant differences in Km and C CT between model group and control group before modeling (Km:[48.28±2.29] D vs.[48.82± 1.63] D;CCT:[356.50± 19.13] μm vs.[356.20±21.66] μm;both at P＞0.05).The Km increased to (48.87±2.27) D and CCT decreased to (340.40±19.84)μm at day 14 after modeling,which were significantly different from (46.86±1.47) D and (367.80±23.38)μm (both at P＜0.01).The maximal deformation amplitude of model group and control group was (1.25±0.07) mm and (1.15 ±0.13) mm,respectively,showing a considerable difference between them (t=2.65,P＜0.05).No significant differences were found in applanation 1/2 time,applanation 1/2 length,applanation velocity,radius of curvature and peak distance between the two groups (all at P＞0.05).The morphology and ultrastructure examinations revealed that the arrangement of collagen fibers was loose and disorder and the interfiber space was enlarged in comparison with control group.Conclusions Collagenase type Ⅱ can lower corneal biomechanical properties.Soaking of cornea with collagenase type Ⅱ may be a potential way to establish a keratectasia animal model.
ABSTRACT
@#AIM: To investigate the changes of corneal biomechanical properties before and after femtosecond laser assisted LASIK(FS-LASIK)using Corneal Visualisation Scheimpflug Technology(Corvis ST)and Ocular Response Analyzer(ORA), and the correlation with other myopic parameters. <p>METHODS:Sixty three patients(63 eyes)who had myopic femtosecond laser assisted LASIK(FS-LASIK)were enrolled in the study. The right eye of each patient was analyzed in this study. The corneal biomechanical parameters pre-operative and 1mo post-operative was measured with the Corvis ST(Oculus, Wetzlar, Germany)and ORA(Reichert, Buffalo, New York, USA). Comparison of the biomechanical property values before and after surgery was peformed using Paired <i>t</i>-test or Mann-Whitney <i>U</i>. Pearson or Spearman correlations were used to evaluate the relationship between parameters.<p>RESULTS: The postoperative 1<sup>st</sup> A-time, Vin, 2<sup>nd</sup> A length, Vout, HC time and Radius demonstrate significant decreases comparing with preoperative values(<i>P</i>=0.00, <i>P</i>=0.00, <i>P</i>=0.00, <i>P</i>=0.00, <i>P</i>=0.00, <i>P</i>=0.00 respectively). The postoperative 2<sup>nd</sup> A-time, DA and PD significantly increases(<i>P</i>=0.00, <i>P</i>=0.00, <i>P</i>=0.00), however, the 1<sup>st</sup> A length had no significant difference after surgery. The CH and CRF were significantly lower after FS-LASIK(<i>P</i>=0.00, <i>P</i>=0.00). A statistically significant correlation coefficient was found between preoperative central corneal thickness(CCT)with postoperative-preoperative changes of 1<sup>st</sup> A-time, 2<sup>nd</sup> A-time, DA and Radius respectively(<i>P</i>=0.01, <i>P</i>=0.04, <i>P</i>=0.03, <i>P</i>=0.01). <p>CONCLUSION:There were significantly changes of corneal biomechanical properties after FS-LASIK surgery. The changes of corneal biomechanical properties after FS-LASIK can be reflected by some parameters of Corvis ST and ORA. The mainly influence of corneal biomechanical alteration was possibly correlation with corneal thickness.
ABSTRACT
Cornea is a very important component of the human eyeball wall.It maintains the physiological structure of eyeball and provides protection for eye content and it is an important part of refractive media.As human inhomogeneous viscoelastic material, the cornea possesses many biomechanical properties such as the elastic, viscosity and non linear elastic.Currently, ocular response an-alyzer and corneal visualization scheimpflug technology are often used in vivo measurement and analysis to assist in the diagnosis and treatment of clinical diseases such as keratoconus, and to assess the feasibility and prognosis of refractive surgery.The latest progress of corneal biomechanical measurement and its clinical application are reviewed in this paper.
ABSTRACT
Cornea is the major refractive components of the eye. As a viscoelastic tissue, cornea exhibits complicated biomechanical properties: non - linear elasticity, anisotropy and viscoelasticity. The biomechanical properties play an important role in keeping the normal structureand function. Changes in biomechanical properties are always earlier than the clinical symptoms. So quantitative measurement of the biomechanical properties benefits the early diagnosis and treatment of diseases. Different methods to measure the biomechanical properties of cornea were reviewed in detail, including classic ex vivo destructive tests, commercially available in vivo measuring methods and other emerging methods with the potential for clinical application but not validated for in vivo measurement. The operating principles, advantages as well as limitations of these methods were also described.