Corneal Visualization Scheimpflug Technology Research Articles

Ultrathin nonectatic cornea with normal slit‐scanning and Scheimpflug-based tomographic findings with suspicious corneal biomechanical properties

A 30-year-old man complained of bilateral defective vision due to bilateral refractive error. The uncorrected distance visual acuity (UDVA) in the right eye was 0.06, with corrected distance visual acuity (CDVA) to 1.00 by a refraction of −2.50 × −2.75 × 15, whereas the UDVA in the left eye was 0.05, with CDVA to 0.80 by a refraction of −4.75 × −2.50 × 64. Corneal tomography was performed for both eyes and showed normal corneal tomography with symmetrical bowtie, but the thinnest pachymetry was extremely low. Corneal tomography examination together with Scheimpflug-based tomography was performed after 1 year and the results were the same. Evaluation of corneal biomechanical properties was performed using corneal visualization Scheimpflug technology. It showed suspicious results, which were mainly explained by this extremely low corneal pachymetry.

Evaluation of new Corvis ST parameters in normal, Post-LASIK, Post-LASIK keratectasia and keratoconus eyes

The aim of this study was to evaluate the distribution of new Corneal Visualisation Scheimpflug Technology (Corvis ST) parameters in normal, Post-laser in situ keratomileusis (LASIK), Post-LASIK keratectasia (KE) and keratoconus (KC) eyes, and explore the diagnostic ability of these parameters in distinguishing KE from LASIK eyes. Twenty-three normal eyes, 23 LASIK eyes, 23 KE eyes and 23 KC eyes were recruited in this study. The following new Corvis ST parameters were measured: Max Inverse Radius, deformation amplitude (DA) Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Ambrosio’s relational thickness horizontal (ARTh), Integrated Radius, stiffness parameter at first applanation (SP-A1) and Corvis biomechanical index (CBI). The general linear model, linear regression model, relation analysis and receiver operating characteristic (ROC) curve were performed. The Max Inverse Radius, DA Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Integrated Radius and CBI in LASIK eyes, KE eyes and KC eyes were higher than in normal eyes, while the ARTh and SP-A1 parameters were lower than in normal eyes. The KE eyes had higher Max Inverse Radius, DA Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Integrated Radius, and lower SP-A1 value than LASIK eyes (all P < 0.05). The central corneal thickness was related to the Pachy Slope (r = −0.485), ARTh (r = −0.766), SP-A1 (r = 0.618) in KE eyes (all P < 0.05). The area under the ROC curve of Integrated Radius, Max Inverse Radius, DA Ratio Max [2 mm] and SP-A1 were above 0.800 in identifying KE from LASIK eyes. Thus, the new Corvis ST parameters were different between LASIK and KE eyes, suggesting that they might be helpful in distinguishing KE eyes from LASIK eyes. However, a further multi-center and large sample study is necessary to confirm these findings.

Corneal biomechanical properties after laser-assisted in situ keratomileusis and small-incision lenticule extraction in myopic eyes

Purpose The aim of this study was to compare the differences in corneal biomechanical changes after laser-assisted in situ keratomileusis (LASIK) and femtosecond laser small-incision lenticule extraction (SMILE) using the corneal visualization Scheimpflug technology (Corvis ST).Patients and methods This is a prospective study that included two groups of myopic patients. Group 1 included 20 eyes that underwent LASIK surgery, and group 2 included 20 eyes that underwent SMILE surgery. The corneal biomechanical properties were assessed preoperatively and three months postoperatively using the Corvis ST in both groups. The main evaluated parameters included the first and second applanation (A1 and A2) time, absolute velocity and length, highest concavity (HC) time and radius, peak (P) distance, HC deflection amplitude, deformation amplitude, and Corvis biomechanical index.Results There was no significant difference between the two groups regarding all preoperative biomechanical parameters measured by Corvis ST. At the third postoperative month, there was no significant difference between the two groups regarding A1 length or absolute velocity, whereas A1 time, A2 time, A2 length, absolute A2 velocity, and HC time were significantly lower among patients in the LASIK group than patients in the SMILE group. On the contrary, HC radius, P distance, HC deflection amplitude, deformation amplitude, and Corvis biomechanical index were significantly higher among patients in the LASIK group than patients in the SMILE group.Conclusion SMILE and LASIK procedures substantially alter the corneal biomechanical properties measured by the Corvis ST. The LASIK procedure seemed to result in less tensile strength and more compliant cornea when compared with the SMILE procedure in myopic corrections. This denotes greater reduction in biomechanical stability in the LASIK procedure than in SMILE.

Repeatability of new Corvis ST parameters and influencing factors in myopia patients

Objective To evaluate the repeatability of corneal biomechanics parameters measured by Corneal Visualization Scheimpflug Technology (Corvis ST) and explore the factors that influence the repeatability. Methods A diagnostic test study was performed.A total of 190 eyes in 95 myopia patients (34 males and 61 females) were enrolled from September to October 2017 in Henan Eye Hospital.All the subjects underwent 5 repeated examinations with the Corvis ST.The intraclass correlation coefficient (ICC), Cronbach α coefficients and repeatability coefficient (RC) were computed to evaluate repeatability of Corvis ST parameters.The multiple linear regression analysis was used to study the factors that affect the magnitude of the test-retest variability (within subject SD) of new Corvis ST parameters.This study was approved by the Ethics Committee of Henan Eye Hospital (HNEECKY-2019[5]), and written informed consent was obtained from each subject. Results Among the 39 biomechanics parameters, The ICC and Cronbach α were greater than 0.75 for 26 parameters, within 0.60-0.75 for 4 parameters, and lower than 0.60 for deflection amplitude max time (DLAMT). The ICC and Cronbach α of DA ratio max[1 mm], DA ratio max [2 mm], max inverse radius, Ambrosio's relational thickness horizontal (ARTh), biomechanical intraocular pressure (bIOP), integrated radius, stiffness parameter applanation 1 (SPA1) and Corvis biomechanical index (CBI)were all above 0.920.The multivariate regression results indicated that the within subject SD of bIOP increased with the increase of IOP (β=0.210, P=0.010). The within subjects SD of DA Ratio Max [1 mm]decreased with the increase of central corneal thickness (CCT) (β=-0.218, P=0.008). The within subjects SD of DA Ratio Max [2 mm]decreased with the increase of CCT(β=-0.295, P<0.001). The within subject SD of CBI decreased with the increase of astigmatism, axial lengths and CCT (β=-0.190、-0.148、-0.428, all P<0.05). Conclusion The Corvis ST parameters showed favorable measurement repeatability in myopia patients, especially for the new parameters.Astigmatism, axial lengths and CCT significantly affected the repeatability of CBI. Key words: Cornea; Biomechanics; Myopia; Repeatability; Test-retest variability; Influence factors

Correlation Between Anterior Chamber Volume and Corneal Biomechanical Properties in Human Eyes.

Purpose: To investigate the correlation between anterior chamber volume (ACV) and corneal biomechanical properties in healthy and primary angle closure (PAC) eyes.Methods: A total of 79 eyes from 55 participants were enrolled in this study, including 24 eyes from 17 PAC patients and 55 eyes from 38 normal subjects. Anterior chamber volume was detected via swept-source anterior segment optical coherence tomography (OCT), and the cornea biomechanical data were obtained via corneal visualization Scheimpflug technology (Corvis ST). A student's t-test, Chi-square test, Pearson's correlation coefficients, and linear regression were used in the statistical analysis.Results: Anterior chamber volume was significantly associated with a lower deformation altitude (DA) (p = 0.033), higher stiffness parameter (SP-A1) (p = 0.005), younger age (p = 0.001), and higher biomechanical intraocular pressure (bIOP) (p = 0.001). PAC patients were suspected to have a much shallower anterior chamber than healthy participants. In the PAC group, the mean ACV (p < 0.01), SP-A1 (p < 0.01), and bIOP values (p = 0.01) were significantly reduced as compared to the normal group, and DA values (p = 0.02) and age (p = 0.01) were increased as compared to the normal group.Conclusions: Bigger ACV was associated with lower DA values and age, as well as higher SP-A1 and bIOP values. Reduced corneal stiffness was more commonly found in the PAC suspects as compared to their normal counterparts, indicating a protective physiological mechanism for people with shallower anterior chambers that protects against potential elevations of IOP.

Evaluation of the sensitivity and specificity of corneal visualization scheimpflug technology biomechanical index in the diagnosis of keratoconus

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. Key words: Corneal visualization scheimpflug technology; Corneal biomechanics; Keratoconic diagnosis; Corvis biomechanical index; Sensitivity; Specificity

Study on corneal biomechanical properties of suspicious keratoconus patients in corneal topography

Objective: To explore the characteristics and significance of corneal biomechanics in patients with suspicious total deviation value in Belin/Ambrosio Enhanced Ectasia Display of Pentacam corneal topography. Methods: In this cross-sectional study, 206 patients (325 eyes) with myopia or myopic astigmatism were collected from refractive surgery center of Tianjin Eye Hospital. Among them, 110 males(213 eyes) and 96 females (153 eyes) were aged (22.68±5.20) years. 57 patients (71 eyes) with a total deviation value of 1.6-3.0 in the Pentacam corneal topography were included in the suspicious group, and 149 patients (254 eyes) of<1.6 were included in the control group. The values of the first applanation time (A1-Time), first applanation length (A1-Length), first applanation velocity (A1-Velocity), second applanation time (A2-Time), second applanation length (A2-Length), second applanation velocity(A2-Velocity), highest concavity time (HC-time), highest concavity deformation amplitude (DA), highest concavity peak distance (PD), highest concavity radius (HC-Radius, RoC), intraocular pressure were measured using the corneal visualization Scheimpflug technology. The total deviation value in Belin/Ambrosio Enhanced Ectasia Display were measured with a Pentacam. The biomechanical parameters of the suspicious group were compared with the normal group by the two independent samples t test and the identity regression analyses. The data correlation was performed using Pearson linear correlation analysis. Results: Compared with the D normal group, the K1, K2 and Km of D suspicious group were significantly increased (P<0.001). A1-Velocity [(0.152±0.015) m/s] and DA[(1.050±0.090) mm] were significantly increased (t=4.348, 2.708; P<0.001, 0.007), while the CCT, A1-Length, A2-Length and RoC were significantly decreased (P<0.01) in suspicious group. In suspicious group, there was a significant correlation between A1-Time, A1-Length, A2-Length, A2-Velocity, IOP and CCT(r=0.305, 0.324, 0.238, 0.346, 0.316; P<0.05). There was a significant correlation between the anterior surface refractive power K1 and the A1-Length (r=-0.361, P=0.002), and there was a significant correlation between the A1-Length, RoC and anterior surface refractive power K2 (r=-0.369, -0.242; P=0.002, 0.043). There was a significant correlation between anterior surface refractive power Km and A1-Length (r=-0.373, P=0.001). After adjusting the confounding factors between two groups by the identity regression analyses, the A1-Length (P=0.003), A1-Velocity (P<0.001) and DA (P=0.002) were still significant differences. Conclusions: In total deviation value suspicious group, the corneal thickness was thinner, corneal curvature became steeper and the corneal biomechanical properties were weaker. It is important to screen keratoconus before corneal refractive surgery and choose a reasonable surgical procedure to reduce corneal dilatation after refractive surgery. (Chin J Ophthalmol,2019, 55: 442-447).

Evaluation of corneal elastic modulus based on Corneal Visualization Scheimpflug Technology

BackgroundCorneal biomechanical properties are important for the diagnosis of corneal diseases, individualized design and prognosis of corneal surgery. Clinical available devices such as Ocular Response Analyzer (ORA) and Corneal Visualization Scheimpflug Technology (Corvis ST) can provide corneal biomechanics related parameters, while corneal elastic modulus cannot be extracted directly from them at present. The aim of this study is to suggest a method to determine corneal elastic modulus based on the results of Corvis ST test according to Reissner’s theory on the relation between stress and small displacement in shallow spherical shell.ResultsFive rabbits (10 eyes) and 10 healthy humans (20 eyes) were measured with Corvis ST to obtain the normal range of corneal elastic modulus. Results showed Corneal elastic modulus of rabbit was 0.16 MPa to 0.35 MPa, human corneal elastic modulus was 0.16–0.30 MPa. Rabbit corneas were also measured at different intraocular pressures (IOP), and results showed corneal elastic modulus, first applanation time (A1T) and stiffness parameter (SP-A1) were positively correlated with IOP. Deformation amplitude (DA), the second applanations time (A2T), and peak distance (PD) were negatively correlated with IOP. Finite element method was used to simulate the Corvis measurements according to the calculated elastic modulus and the simulated corneal apical displacements were agreement with experimental results in general.ConclusionsThe method to determine corneal elastic modulus based on Corvis test according to the relationship between force and displacements of shallow spherical shell is convenient and effective.

The associations between corneal biomechanical parameters and glaucoma

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. Key words: Glaucoma; Corneal biomechanical parameters; Ocular response analyzer; Corneal visualization scheimpflug technology

Small-Incision Femtosecond Laser-Assisted Intracorneal Concave Lenticule Implantation in Patients With Keratoconus.

To evaluate the feasibility and efficacy of small-incision femtosecond laser-assisted intracorneal concave lenticule implantation (SFII) and penetrating keratoplasty (PKP) in patients with progressive keratoconus. All the patients were clinically diagnosed with progressive keratoconus. Twenty patients underwent PKP (PKP group), and 11 patients underwent SFII (SFII group). Visual acuity, intraocular pressure, corneal topography, corneal visualization Scheimpflug technology, anterior segment optical coherence tomography, and in vivo confocal microscopy were analyzed. Vision improved at 3 months postoperatively in the SFII group. In the PKP group, corrected distance visual acuity improved 1 week after surgery. Corneal topography showed a statistically significant decrease in the anterior K1 and K2. Corneal visualization Scheimpflug technology showed that changes in the biomechanical parameters of the SFII group were also statistically different from those of the PKP group. All the grafts from both groups were clearly visible by anterior segment optical coherence tomography observation. The central corneal thickness of both groups was stable during the 24-month study period. In vivo confocal microscopy showed a few dendritic cells in the subepithelial region in the SFII group. At 3 months after surgery, many dendritic cells and inflammatory cells were observed in the basal epithelium and stroma in the PKP group. Both SFII and PKP surgical procedures resulted in a stable corneal volume and improved visual acuity in this long-term study. SFII was less invasive and more efficient compared with PKP.

Biomechanical changes in the cornea following cataract surgery: A prospective assessment with the Corneal Visualisation Scheimpflug Technology.

Intraocular pressure (IOP) is often reduced following cataract surgery. Postoperative changes in corneal stiffness are likely to be at least partly responsible for any reduction in IOP measured with applanation tonometry. To determine the effect of cataract surgery and corneal incision size on corneal biomechanics. Prospective randomized trial. One hundred prospectively enrolled patients qualifying for cataract surgery. Participants were randomized to clear corneal incisions with a 2.20 or 2.85 mm keratome. Corneal Visualisation Scheimpflug Technology (Corvis-ST) tonometry and dynamic corneal response measurements were obtained preoperatively, and 3 mo postoperatively. Multiple regression analysis was completed using R software. Corvis-ST biomechanical parameters. Ninety-three eyes of 93 patients were included in the final analysis. Mean Corvis-ST biomechanically corrected IOP decreased by 3.63 mmHg postoperatively (95% confidence interval = 2.97-4.35, P ≤ 0.01), and central pachymetry increased by 6.96 μm (4.33-9.59, P ≤ 0.01). Independent of IOP and pachymetry changes, mean (±SE) corneal first applanation stiffness parameter reduced by 9.761 ± 3.729 (P = 0.01) postoperatively. First applanation velocity increased by 0.007 ± 0.002 ms, second applanation velocity increased by 0.012 ± 0.004 ms (P ≤ 0.01), the first applanation deformation amplitude increased by 0.008 ± 0.002 mm (P ≤ 0.01) and the deflection amplitude at highest concavity increased by 0.030 ± 0.069 (P ≤ 0.01). There were no significant differences between different incision size groups. Corneal stiffness is reduced 3 mo following cataract surgery and is associated with falsely low IOP measurements. This finding may be important for glaucoma patients and in particular when assessing the effectivity of minimally invasive glaucoma surgery devices.

Effect of Intravitreal Bevacizumab Injection on Corneal in vivo Biomechanics: A Pilot Study.

Purpose:To evaluate the effect of intravitreal bevacizumab (IVB) injection on corneal biomechanical parameters as measured by the ocular response analyzer (ORA) and Corneal Visualization Scheimpflug Technology (CorVis).Methods:In this prospective pilot study, ORA and CorVis parameters were recorded before and after a three-month course of IVB injection therapy in 16 patients in the injected and the contralateral non-injected control eyes. The changes in the recorded parameters in each group and the differences between the two groups were evaluated and compared.Results:None of the changes in ORA parameters were statistically significant in the injected and non-injected groups before and three months after injection, except for corneal resistance factor (CRF) in injected eyes (paired t-test, P = 0.039). The differences in corneal hysteresis (CH) and CRF were not statistically significant between the two groups (P = 0.441 and 0.236, respectively), but significant differences were noted between corneal compensated IOP (IOPcc) and Goldmann-correlated IOP (IOPg) (P = 0.045 and 0.047, respectively). None of the changes in CorVis parameters were statistically significant in the groups before and at the end of study, except for the time of first corneal applanation (TAp1 ms) in the injected group (P = 0.040, paired t-test). Differences in TAp1, length of the second corneal applanation (LAp2 mm), velocity of the second corneal applanation (VAp2 m/s), intraocular pressure (IOP), and central corneal thickness (CCT) also showed borderline significance between the two groups.Conclusion:In this pilot study IVB injection could change CRF, IOPcc, IOPg, and TAP1 as measured by ORA and CorVis.

Correlation analysis between corneal biomechanical properties and high-order aberration in myopia

Objective To investigate the correlations between corneal biomechanical properties and corneal high-order aberrations (HOAs) in myopic eyes. Methods In this retrospective study, 263 right eyes with myopia or myopic astigmatism were enrolled from January to October 2015 in Tianjin Eye Hospital.The values of first applanation time (A1T), first applanation length (A1L), first applanation velocity (A1V), second applanation time (A2T), second applanation length (A2L), second applanation velocity (A2V), highest concavity time (HCT), highest concavity deformation amplitude (HCDA), highest concavity peak distance (HCPD), highest concavity radius (HCR) and non-contact intraocular pressure (IOPnct) were measured using the corneal visualization Scheimpflug technology (Corvis ST). The central corneal thickness (CCT) and wavefront aberrations of the anterior, posterior surface, and the total cornea were measured with Pentacam.Pearson correlation and stepwise multivariate linear regression analysis were applied to analyze the correlations between biomechanical properties and corneal HOAs.This study follows the Helsinki declaration.The experiment was approved by the Ethic Committee of Tianjin Eye Hospital.Informed consent was signed from each patient. Results There was a correlation between biomechanical properties and corneal HOAs.Negative correlations were found between A1L and the spherical aberration, HOAs RMS of anterior surface, total RMS and HOAs RMS of the posterior surface and HOAs RMS of the total cornea (P<0.05). HCRs were negatively correlated with total RMS of the total cornea and the anterior surface (P<0.05). The A2V was correlated with various aberrations.Multiple stepwise linear regression model analysis showed that, the correlation between the aberrations of anterior surface and biomechanical parameters, and the correlations between the total corneal aberration and biomechanical parameters were weak, the correlations between the aberrations of posterior surface and biomechanical parameters were strong. Conclusions There is a correlation between the biomechanical properties and corneal HOAs.The changes of the corneal biomechanical properties are mainly associated with the posterior corneal aberrations, which may contribute to the early diagnosis of subclinical keratoconus or dilated corneal disease. Key words: Corneal biomechanical properties; Aberration; Visual quality

Corneal Stiffness and Its Relationship With Other Corneal Biomechanical and Nonbiomechanical Parameters in Myopic Eyes of Chinese Patients.

To investigate corneal stiffness and analyze its possible influence on other corneal biomechanical and nonbiomechanical parameters in myopic eyes of Chinese patients. A total of 387 healthy (right) myopic eyes were included in this study. Corneal visualization Scheimpflug technology was used to measure the corneal stiffness parameter at the first applanation (SP-A1), deformation amplitude ratio at 1.0 and at 2.0 mm, biomechanically corrected intraocular pressure (bIOP), and corneal deformation parameters during the first applanation (A1: A1-time, A1-length, and A1-velocity), second applanation (A2; A2-time, A2-length, and A2-velocity), and highest concavity (HC; HC-time, HC-radius, HC deformation amplitude, and HC peak distance). The Pentacam was used to evaluate central corneal thickness, mean corneal curvature (Km), anterior corneal central elevation, and corneal asphericity (Q value) of the anterior cornea. The mean SP-A1 and bIOP values were 90.46 ± 15.39 mm Hg/mm and 13.5 ± 1.85 mm Hg, respectively. The SP-A1 increased with age (β = 0.41 [95% CI, 0.28%-0.54%]; P < 0.0001). Corneal stiffness was positively correlated with central corneal thickness, uncorrected intraocular pressure, and bIOP and was also significantly correlated with all corneal deformation parameters (P < 0.05), except A1-length, HC-time, and HC peak distance. Corneal stiffness was negatively correlated with central corneal elevation of the anterior surface (r = -0.124, P = 0.014) and mean corneal curvature (r = -0.114, P = 0.025) and positively correlated with the Q value of the anterior surface (r = 0.109, P = 0.032). Corneal stiffness increased with age. Stronger corneal stiffness may be related to flattening of the cornea and higher intraocular pressure.

Change of corneal biomechanical properties caused by phacoemulsification using corneal visualization Scheimpflug technology

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). Conclusions Corneal biomechanical properties occur change in the early stage after phacoemulsification and return to normal in postoperative 1 month . Key words: Corneal biomechanics; Cataract/surgery; Phacoemulsification; Corneal visualization Scheimpflug technology

Research of diagnostic value of corneal biomechanical parameters based on Corvis ST in keratoconus

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 (A1L), 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). 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%. Conclusions 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. Key words: Corneal visualization Scheimpflug technology; Keratoconus; Corneal biomechanics

Feasibility of constructing keratectasia animal model using collagenase type II

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 collagenase 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 hematoxylin-eosin staining and transmission electron microscopic examination. Results There were no significant differences in Km and CCT 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 0.05). 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. Key words: Biomechanical properties; Cornea/pathology; Collagenase type Ⅱ; Deformation amplitudes; Keratoconus; Keratectasia/chemical induced; Rabbits; Corneal visualization Scheimpflug technology

Keratoconus Screening With Dynamic Biomechanical In Vivo Scheimpflug Analyses: A Proof-of-Concept Study.

This proof-of-concept study was designed to analyze the ability of in vivo biomechanical corneal analyses with the corneal visualization Scheimpflug technology (CorvisST; Oculus Optikgeräte, Wetzlar, Germany) to differentiate between normal eyes and eyes with manifest keratoconus after strictly eliminating the potential confounding factors intraocular pressure (IOP) and central corneal thickness (CCT). In this retrospective, cross-sectional study, after pairwise matching for CCT and IOP, 29 normal eyes and 29 keratoconic eyes (one eye from each patient) were selected as study population. Older CorvisST parameters and the new Corvis Biomechanical Index (CBI), including several biomechanical and one tomographic parameter, as well as an adjusted CBI (aCBI) (including only biomechanical parameters), were compared regarding their discriminative ability between both groups. None of the CorvisST parameters of the former software version demonstrated statistically significant differences between normal and keratoconic eyes. On the other hand, the CBI and aCBI reached accuracies of 0.91 and 0.93, respectively, to discriminate between CCT- and IOP-matched normal and keratoconic eyes (CBI: [AUC/sensitivity/specificity]: 0.961/0.90/0.93; aCBI: [AUC/sensitivity/specificity]: 0.986/0.93/0.93). This study demonstrated that the concept of keratoconus screening with the CorvisST is effective in differentiating keratoconic from non-keratoconic eyes. The next steps will be testing the indices in subclinical keratoconus cases and hopefully combining biomechanical analyses with already established topography and tomography indices to further improve current keratoconus screening. [J Refract Surg. 2017;33(11):773-778.].

Application of Corvis ST to evaluate the effect of femtosecond laser-assisted cataract surgery on corneal biomechanics.

The aim of the present study was to evaluate the effects of femtosecond laser-assisted cataract surgery (FLACS) and phacoemulsification on corneal biomechanics using corneal visualization Scheimpflug technology. The medical records of 50 eyes from 50 patients who received phacoemulsification and intraocular lens implantation because of age-related factors between June 2014 and September 2014 were retrospectively analyzed. FLACS was used in 12 eyes (FLACS group), and conventional phacoemulsification in 38 eyes (PHACO group). The evaluation of corneal biomechanical parameters included the first/second applanation time (A-time1/A-time2), the first/second applanation length (A-length1/A-length2), corneal velocity during the first/second applanation moment (Vin/Vout), highest concavity time, highest concavity-radius (HC-radius), peak distance (PD), deformation amplitude (DA), central corneal thickness (CCT), and intraocular pressure (IOP). The differences in A-length1/A-length2, IOP, CCT, PD, and DA were significant in the PHACO group between those before, 1 week after, and 1 month after surgery. No significant differences in corneal biomechanical parameters were found between those at 1 month after surgery and before surgery. There were significant differences in IOP and CCT in the FLACS group between those before, 1 week after, and 1 month after surgery. There were no significant differences in the other corneal biomechanical parameters. No significant differences were found in corneal biomechanical parameters between those 1 month after surgery and before surgery. There were significant differences in A-length1/A-length2, CCT, PD, and DA between the two groups at 1 week after surgery. There were no significant differences in corneal biomechanical parameters between the two groups at 1 month after surgery. In conclusion, the effect of FLACS on corneal biomechanics is smaller than that of phacoemulsification. The corneal biomechanical parameters are restored to preoperative levels with the healing of the incision, and the reduction of swelling of the tissue near the incision.

Keratoconus diagnosis using Corvis ST measured biomechanical parameters

PurposeTo assess the diagnostic power of the Corneal Visualization Scheimpflug Technology (Corvis ST) provided corneal biomechanical parameters in keratoconic corneas. MethodsThe following biomechanical parameters of 48 keratoconic eyes were compared with the corresponding ones in 50 normal eyes: time of the first applanation and time from start to the second applanation [applanation-1 time (A1T) and applanation-2 time (A2T)], time of the highest corneal displacement [highest concavity time (HCT)], magnitude of the displacement [highest concavity deformation amplitude (HCDA)], the length of the flattened segment in the applanations [first applanation length (A1L) and second applanation length (A2L)], velocity of corneal movement during applanations [applanation-1 velocity (A1V) and applanation-2 velocity (A2V)], distance between bending points of the cornea at the highest concavity [highest concavity peak distance (HCPD)], central concave curvature at the highest concavity [highest concavity radius (HCR)]. To assess the change of parameters by disease severity, the keratoconus group was divided into two subgroups, and their biomechanical parameters were compared with each other and with normal group. The parameters' predictive ability was assessed by receiver operating characteristic (ROC) curves. To control the effect of central corneal thickness (CCT) difference between the two groups, two subgroups with similar CCT were selected, and the analyses were repeated. ResultsOf the 10 parameters compared, the means of the 8 were significantly different between groups (P < 0.05). Means of the parameters did not show significant difference between keratoconus subgroups (P > 0.05). ROC curve analyses showed excellent distinguishing ability for A1T and HCR [area under the curve (AUC) > 0.9], and good distinguishing ability for A2T, A2V, and HCDA (0.9 > AUC > 0.7). A1T reading was able to correctly identify at least 93% of eyes with keratoconus (cut-off point 7.03). In two CCT matched subgroups, A1T showed an excellent distinguishing ability again. ConclusionsThe A1T seems a valuable parameter in the diagnosis of keratoconic eyes. It showed excellent diagnostic ability even when controlled for CCT. None of the parameters were reliable index for keratoconus staging.