Highest Concavity Deformation Amplitude Research Articles

Analysis of Corneal Deformation in Paediatric Patients Affected by Maturity Onset Diabetes of the Young Type 2

To evaluate corneal deformation in Maturity Onset Diabetes of the Young type 2 (MODY2), paediatric subjects were analysed using a Scheimpflug-based device. The purpose of this analysis was to find new biomarkers for MODY2 disease and to gain a better understanding of the pathogenesis of the disease. A total of 15 patients with genetic and metabolic diagnoses of MODY2 (mean age 12.8 ± 5.66 years) and 15 age-matched healthy subjects were included. The biochemical and anthropometric data of MODY2 patients were collected from clinical records, and a complete ophthalmic check with a Pentacam HR EM-3000 Specular Microscope and Corvis ST devices was performed in both groups. Highest concavity (HC) deflection length, Applanation 1 (A1) deflection amplitude, and A1 deflection area showed significantly lower values in MODY2 patients compared to healthy subjects. A significant positive correlation was observed between Body Mass Index (BMI) and HC deflection area and between waist circumference (WC) and the following parameters: maximum deformation amplitude, HC deformation amplitude, and HC deflection area. The glycosylated hemoglobin level (HbA1c) showed a significant positive correlation with Applanation 2 time and HC time. The obtained results show, for the first time, differences regarding corneal distortion features in the MODY2 population compared with healthy eyes.

Analysis of Corneal Distortion after Myopic PRK

The purpose of the study is to evaluate the corneal biomechanical properties (CBP) and their behaviors after myopic refractive surgery both with Ocular Response Analyzer (ORA) and Corvis ST (CST). This retrospective study included 145 eyes of 145 patients with a mean age of 33.13 ± 9.24 years, who underwent myopic photorefractive keratectomy (PRK) for a refractive defect, measured as spherical equivalent, of mean −4.69 ± 2.04 D and have been evaluated before surgery and at 1, 3 and 6 months follow-up. Corneal hysteresis (CH) and corneal resistance factor (CRF) values significantly decreased after 1 month and remained statistically stable during further follow-ups. CST parameters had a different evolution: only second applanation time (AT2) differences showed a significant variation after 1 month that did not statistically change over time. Highest concavity deformation amplitude (HCDA), highest concavity peak distance (HCPD), first applanation time (AT1) and velocity (AV1) showed continuous significant differences both after 3 and after 6 months. This study suggests that after central surface ablation surgery, such as myopic PRK, corneal shape is remodeling, and its deformation parameters are going to change even at 6 months follow-up. This indicates that it should be important to evaluate refractive surgery patients during a longer follow-up because this could allow earlier diagnosis and better management of late-onset complications.

Factors Influencing Corneal Biomechanics in Diabetes Mellitus.

Diabetes mellitus (DM) induces changes in corneal biomechanical properties. The influence of disease-specific factors was evaluated, and a novel DM index was created. Eighty-one patients with DM and 75 healthy subjects were matched according to age, intraocular pressure, and central corneal thickness. Information on the disease was collected, and measurements with the Ocular Response Analyzer and the Corvis ST were taken. Results were compared between the groups, and the influence of disease-specific factors was evaluated. From dynamic corneal response parameters, a DM index was calculated. In DM, corneal hysteresis was higher than in healthy subjects (10.5 ± 1.9 vs. 9.7 ± 1.9 mm Hg, P = 0.008). In addition, dynamic corneal response parameters showed significant differences. Among others, highest concavity (HC) (17.212 ± 0.444 vs. 16.632 ± 0.794 ms, P < 0.001) and A2 time (21.85 ± 0.459 vs. 21.674 ± 0.447 ms, P = 0.017) as well as A1 (0.108 ± 0.008 vs. 0.104 ± 0.011 mm, P = 0.019) and A2 deflection amplitudes (0.127 ± 0.014 vs. 0.119 ± 0.014 mm, P < 0.001) were increased in DM. In DM type 1, HC deformation amplitude (1.14 ± 0.19 vs. 1.095 ± 0.114 mm, P = 0.035) was higher than in type 2. The time of deflection amplitude max correlated with the severity of retinopathy (R = 0.254, P= 0.023). In case of diabetic maculopathy, A1 velocity (0.155 ± 0.018 vs. 0.144 ± 0.019 ms, P = 0.043) and A2 time (22.052 ± 0.395 vs. 21.79 ± 0.46 ms, P = 0.04) were increased. Deformation amplitude max (R = 0.297, P = 0.024), HC time (R = 0.26, P = 0.049), HC deformation amplitude (R = 0.297, P = 0.024), and A2 deformation amplitude (R = 0.276, P = 0.036) were associated to disease duration. The DM index revealed a sensitivity of 0.773 and a specificity of 0.808 (area under the curve of receiver operating characteristic = 0.833). In DM, changes in corneal biomechanics were correlated with disease-specific factors. The DM index achieved reliable sensitivity and specificity values.

Influence factors and differences of posterior corneal elevation measured by Pentacam system combined with Corvis ST

Objective: To investigate the influence factors and differences of abnormal posterior corneal elevation by Pentacam system and Corvis ST. Methods: This retrospective case series study included 227 eyes of 144 patients (90 males, 139 eyes; 54 females, 88 eyes) from December 2017 to October 2018 who were going to receive corneal refractive surgery at the Corneal Refraction Department of Qingdao Eye Hospital. The general data of the patients including gender, age, refractive parameters, optimal correction of spherical and cylindrical diopters were collected. All patients underwent Pentacam system and Corvis ST measurement. According to the back difference (BD) of Pentacam parameters, BD<12 μm was set as the control group (59 patients, 118 eyes) and BD≥12 μm as the high BD group (85 patients, 109 eyes). In the high BD group, BD≤16 μm was set as the suspicious group (44 patients, 53 eyes), while BD>16 μm was set as the abnormal group (41 patients, 56 eyes). Seven parameters of Pentacam and 15 parameters of Corvis ST were selected. The Pentacam parameters included BD, anterior surface keratometry (ASK), posterior surface keratometry (PSK), anterior surface astigmatism (AAstig), posterior surface astigmatism (PAstig), central corneal thickness (CCT), and corneal diameter (W-W). The parameters of Corvis ST included the first applanation time (AT(1)), the first applanation length (AL(1)), the first applanation velocity (AV(1)), the second applanation time (AT(2)), the second applanation length (AL(2)), the second applanation velocity (AV(2)), highest concavity time (HCT), highest concavity peak distance (HC-PD), highest concavity deformation amplitude (HC-DA), highest concavity radius (HC-R), the ratio of deformation amplitude (DA ratio), Integr. Radius, corneal thickness thinnest/pachymetric progression (ARTh), SPA1 (resultant pressure divided by deflection amplitude at the first applanation), and the Corvis Biomechanical Index (CBI). The comparison between the groups was analyzed with Independent sample t test, Kruskal-Wallis H test, and Bonferroni test. Spearman rank correlation analysis was used to explore the correlation factors of BD, and the main factors affecting BD were found through multiple linear regression. Results: There were no statistically significant differences between the control group and the high BD group in age, spherical diopters, and cylindrical diopters (t=-3.311, -1.808, -2.359; P=0.071, 0.072, 0.121, respectively). In Pentacam parameters, ASK, PSK, PAstig, and W-W showed significant differences among groups (Z=18.492, 31.547, 10.773, 70.167; P<0.05). AAstig and CCT showed no statistical difference between groups (P>0.05). Compared with the control group [42.80 (41.98, 44.00)], ASK increased in the abnormal group [43.40 (42.20, 44.40)] significantly (t=-4.292; P<0.05). PSK of the suspicious group [-6.50 (-6.60, -6.35)] and the abnormal group [-6.50 (-6.70, -6.33)] increased significantly compared with the control group [-6.30 (-6.50, -6.20)] (t=4.492, 4.618; P<0.05). Compared with the control group [0.40 (0.30, 0.50)], PAstig of the suspicious group [0.40 (0.30, 0.40)] and the abnormal group [0.40 (0.30, 0.40)] increased significantly (t=2.796, 2.515; P=0.016, 0.036). Compared with the control group [11.50 (11.40, 11.80)], W-W of the suspicious group [11.40 (11.00, 11.60)] and the abnormal group [11.10 (10.90, 11.30)] decreased, and W-W of the abnormal group also decreased significantly compared with the suspicious group (t=3.235, 8.353, 4.282; P<0.05). The correlation analysis between BD and Pentacam parameters of patients in each group showed that BD was negatively correlated with W-W (r=-0.614, -0.304, -0.396, -0.661, P<0.05) in the control group, the suspicious group, the abnormal group, and all patients, while BD had a low correlation with other parameters or no significant correlation. The correlation analysis of BD and Corvis ST parameters in patients showed that only in the suspicious group, BD was positively correlated with AV(1), HCT, and HC-DA (r=0.332, 0.361, 0.382, P<0.05), while no significant correlation was found between BD and other Corvis ST parameters in each group. In order to further explore the main factors affecting BD, Pentacam parameters and Corvis ST parameters were selected as independent variables with BD as the dependent variable to establish a multivariate linear regression analysis model. There was no collinearity between variables W-W, ASK, PSK, HC-PD, SPA1, and CCT (tolerance<0.100). The equation test result was F=37.221, P<0.001, adjusted r(2)=0.504, and the fitting was good. Conclusions: Among the Pentacam parameters, W-W, ASK, and PSK are the main factors affecting the change of BD. HC-PD and SPA1 in the Corvis ST parameters may also have some influence on BD. The Pentacam system combined with Corvis ST is a very useful differential diagnosis system for patients with abnormal BD. (Chin J Ophthalmol, 2020, 56:110-117).

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 biomechanical properties modification following intrastromal correction of presbyopia using femtosecond laser

Objective To investigate the changes of corneal biomechanics of intrastromal correction (INTRACOR) femtosecond technique to treat presbyopia. Methods A prospective, clinical self-control clinical trial was designed.Twenty-four presbyopic patients with emmetropia or mild hyperopia were enrolled in this study.The INTRACOR procedure was performed using the Technolas femtosecond laser in the nondominant eye.Uncorrected distance visual acuity (UCDVA), uncorrected near visual acuity (UCNVA) and spherical equivalent (SE) were recorded in preoperation and postoperative 12 months, and the quality of life of postoperative patients was evaluated.The corneal deformation parameters including highest concavity deformation amplitude (HC-DA), highest concavity peak distance (HC-PD), highest concavity radius (HC-R), non-contact intraocular pressure and the central corneal thickness (CCT) were measured using the Corvis ST visualization biomechanical analyzer in preoperation and postoperative 1 month, 3, 6 and 12 months, respectively.This study followed the Declaration of Helsinki.Written informed consent was obtained from each subject prior to entering study cohort.This study protocol was approved by Ethic Committee of Affiliated Eye Hospital of Shandong University of Traditional Chinese Medicine (No.SDZYYDXYKYYLL2011.06). Results Compared with preoperation, UCNVA of all 24 (100%) eyes was improved at 12 months postoperatively with minimal or no change in UCDVA.The mean spherical equivalent was (+ 0.35 ± 0.29)D and (-0.37 ± 0.29)D before and 12 months after operation, with a significant difference beteeen them (t=-7.39, P 0.05). Compared with preoperation, the postoperative 1 month, 3, 6, 12 months HC-R values were significantly declined, HC-DA values were significantly increased, with significant differences between them (all at P 0.05). Corneal aspherical index (Q Value) was -0.28±0.10 at 12 months postoperatively, which was increased compared with the preoperation, and the maximum value added value (diff-K) of the central corneal curvature was (2.55±0.81)D. Conclusions INTRACOR treatment of presbyopia can effectively improve near vision, increase postoperative corneal biomechanical maximum HC-R and HC-DA, negatively increase the corneal central curvature increased aspheric index, which suggests that corneal biomechanics of central cornea is weakened after intrastromal femtosecond presbyopic treatment, and the hyperprolate mutifocal corneal shape is formed under normal intraocular pressure. Key words: Presbyopia; Femtosecond laser; Intrastromal correction; Perspective study; Corneal biomechanics; Corneal aspherical index

Comparison among Ocular Response Analyzer, Corvis ST and Goldmann applanation tonometry in healthy children.

To explore the relationship between different parameters of Ocular Response Analyzer (ORA) and Corvis ST (CST) in a sample of healthy Iranian school-aged children and the relationship between parameters of these 2 instruments against intraocular pressure (IOP), measured by the Goldmann applanation tonometer (GAT-IOP), age and gender, and find possible correlation between ORA and CST with GAT. This cross-sectional study included 90 healthy children. A general interview and complete eye examination were performed. Following successful GAT-IOP measurement, ORA and CST were conducted. The CST parameters were A 1/2 length (A1L, A2L), A 1/2 velocity (A1V, A2V), highest concavity deformation amplitude (HCDA), radius of curvature (RoC), peak distance (PD), central corneal thickness (CCT) and IOP. The ORA parameters were corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated IOP (IOP-G) and corneal compensated IOP (IOP-CC). Extracted data was analyzed using the Statistical Package for Social Science software. Totally 39 males with age of 9.08±1.60 (6-12)y and 51 females with age of 8.96±1.55 (6-13)y were included. Many CST parameters were significantly correlated with CH, CRF, IOP-G and IOP-CC. Some CST parameters had a significant correlation with GAT-IOP, including IOP-CST in both eyes and HCDA, A2L, PD, and RoC in the left eye, but none with age, except A2L in the right eye. The CRF measurement showed a significant correlation with GAT-IOP in both eyes and CH in the right eye, yet, none with age. Among all CST and ORA parameters, CCT-CST in both eyes and A1L in right eye had a significant correlation with gender, although this was a negligible negative correlation. Comparison of mean IOP values by different devices showed a significantly highest IOP overestimation by CST and lowest by IOP-CC compared with GAT. Also, IOP-G versus IOP-CST significantly had the lowest IOP overestimation among others. Overall, either low positive correlation or negligible correlation was found between IOP measurements by 3 instruments. The study finds the highest IOP overestimation by CST and lowest by IOP-CC compared with GAT. Overall, either low positive correlation or negligible correlation is found between IOP measurements by the 3 instruments.

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

Ocular manifestation in Marfan syndrome: corneal biomechanical properties relate to increased systemic score points.

To evaluate corneal deformation to an air puff as a new noninvasive tool to document disease status in Marfan syndrome (MFS) METHODS: Prospective observational cohort study. We included patients diagnosed with MFS who had their routine cardiovascular follow-up and applied the revised Ghent nosology to define two subgroups according to a high (≥ 7) and a low (< 7 points) systemic score. Dynamic Scheimpflug-based biomechanical analyses (CorvisST® [CST; Oculus GmbH]) were performed. The main outcome measure was the displacement of the corneal apex as given by the parameters highest concavity (HC; in ms), peak distance (PD; in mm), and highest concavity deformation amplitude (DA; mm). Forty-three eyes of 43 individuals (19 female, 24 male; mean age 42.0 ± 12.0years, range 18-67years) diagnosed with MFS were included. Applying the Ghent criteria, 21 patients had an advanced systemic score of ≥ 7, and 22 had score points < 7. There were no differences in age or sex between both groups. In contrast, HC was faster (P = 0.004), and PD (P < 0.001) was longer in those individuals with systemic score ≥ 7; maximum DA did not result in a statistically significant difference between the groups (P = 0.250). In vivo noninvasive biomechanical analyses with CST offer a new, non-invasive method to identify pathologic corneal deformation responses in adults with MFS. In the future, corneal deformation to an air puff could thus assist early identification of patients with high Ghent score as an adjunct to existing diagnostic tests.

Association between Corneal Biomechanical Properties with Ocular Response Analyzer and Also CorvisST Tonometry, and Glaucomatous Visual Field Severity.

PurposeTo investigate the association between corneal biomechanical properties measured with the Ocular Response Analyzer (ORA) and also CorvisST (CST) tonometry, and glaucomatous visual field (VF) severity.MethodsOne hundred forty-six eyes of 91 patients with primary open-angle glaucoma who performed Humphrey Field Analyzer 30-2 or 24-2 SITA-Standard, ORA, and CST within 180 days were included in this multicentral, observational cross-sectional study. The association between ORA parameters (corneal hysteresis [CH] and corneal resistant factor [CRF]), CST parameters (A1 and A2 time, A1 and A2 length, A1 and A2 velocity, A1 and A2 deformation amplitude, highest deformation amplitude, highest concavity time, peak distance, and radius), and other basic parameters (age, intraocular pressure with Goldmann applanation tonometry, central corneal thickness, and axial length) against mean total deviation (mTD) were analyzed using a linear mixed-model and model selection with corrected Akaike Information Criterion (AICc).ResultsThe optimal model of VF severity included ORA's CH as well as a number of CST parameters, including A1 length, A2 time, radius, and highest concavity deformation amplitude (AICc: 971.7). The possibility this model describes visual field severity more accurately than the optimal model without CST parameters was 99.98%.ConclusionGlaucomatous VF severity was best described by both ORA and CST parameters. Eyes with corneas that experience sharp and deep indentation at the maximum deformation, wide indentation at the first applanation, and early second applanation in the CST measurement are more likely to show advanced VF severity.Translational RelevanceCorvisST tonometry parameters are related to VF severity in glaucoma patients.

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.

The usefulness of CorvisST Tonometry and the Ocular Response Analyzer to assess the progression of glaucoma

Corneal Visualization Scheimpflug Technology (CST) and Ocular Response Analyzer (ORA) measurements were carried out in 105 eyes of 69 patients with primary open-angle glaucoma. All patients had axial length (AL), central corneal thickness (CCT), intraocular pressure (IOP) with Goldmann applanation tonometry (GAT) and eight visual fields (VF)s with the Humphrey Field Analyzer. VF progression was summarized using a time trend analysis of mean total deviation (mTD) and the association between mTD progression rate and a number of ocular parameters (including CST and ORA measurements) was assessed using mixed linear regression analysis. The optimal model of VF progression selected based on the corrected Akaike Information Criteria (AICc) included ORA’s corneal hysteresis (CH) parameter as well as a number of CST measurements: mTD progression rate = 1.2–0.070 * mean GAT + 0.090 * CH–1.5 * highest concavity deformation amplitude with CST + 9.4 * A1 deformation amplitude with CST–0.05 * A2 length with CST (AICc = 125.8). Eyes with corneas that experience deep indentation at the maximum deformation, shallow indentation at the first applanation and wide indentation at the second applanation in the CST measurement are more likely to experience faster rates of VF progression.

Correlations between the deformation parameters measured by Corvis ST and corneal morphology parameters in myopic patients

Background The novel dynamic biomechanical device Corvis ST can measure a variety of corneal deformation parameters and record the dynamic process of cornea deformation.Understanding various corneal deformation parameters is of important clinical significance for morphological and functional prediction for myopic eyes in corneal refractive surgery.However, the range and meaning of corneal deformation parameters in myopic eyes are still unknown. Objective This study was to establish the range of corneal defamation parameters by Corvis ST and explore its clinical significance in myopic eyes. Methods A descriptive study was designed under the approval of Ethic Committee of Tianjin Eye Hospital and informed consent of patients.This study protocol complied with Helsinki Declaration.Four hundred and seventy-seven eyes of 257 myopic patients who were going to receive corneal refractive surgery were included in Tianjin Eye Hospital from June 2014 to January 2015.The corneal deformation parameters including the first applanation time (1st A-time), first applanation lengh (1st A-length), first applanation velocity (1st A-velocity), second applanation time (2nd A-time), second applanation length(2nd A-length), second applanation velocity (2nd A-velocity), highest concavity time (HC-time), highest concavity deformation amplitude (HC-DA), highest concavity peak distance (HC-PD), highest concavity radius (HC-R), non-contact intraocular pressure (IOPnct) and the central corneal thickness (CCTst) were measured by Corvis ST.Corneal structural parameters including CCT and corneal curvature were measured by 3-D anterior segment analysis system( Pentacam), and corneal biomechanical parameters including corneal resistance factor (CRF), corneal hysteresis (CH), intraocular pressure mimic Goldmann (IOPg) and intraocular pressure of corneal compensation (IOPcc) were measured by Ocular Response Analyzer (ORA). The distributions of the data were tested with the Shapiro-Wilk test and 95% confidence intervals (CI) were calculated.The correlations of the variables were evaluated by Pearson correlation coefficient and Spearman rank correlation coefficient.Multiple linear regression was used to analyze the changes of 1st A-time, 2nd A-time and HC-DA with corneal morphology and biomechanical parameters. Results Only 1st A-time, 2ndA-time, HC-time, HC-DA, CCTst and IOPnct showed the normality distribution in corneal deformation parameters.The positive correlations were found between 1st A-time, 1st A-length, 2nd A-length, 2nd A-velocity, HC-R with CCT (r=0.338, rs=0.129, rs=0.282, rs=0.374, r=0.306, all at P<0.01), while 1st A-velocity, 2nd A-time, HC-D and HC-PD showed the negative correlations with CCT (rs=-0.235, r=-0.130, r=-0.259, r=-0.226, all at P<0.01). CRF and CH showed positive correlations with 1st A-time, 2nd A-length, 2nd A-velocity, HC-time, HC-R and negative correlations with HC-PD, △A-length (all at P<0.05).1st A-time, 2nd A-time and HC-DA changed with CRF and IOPcc with the regression formations of 1st A-time =6.185+ 0.066CRF+ 0.034IOPcc (F=300.123, P=0.000), 2nd A-time=23.397-0.074IOPcc-0.044CRF (F=227.979, P=0.000) and HC-DA= 1.523-0.017IOPcc-0.017CRF (F=152.662, P=0.000). The CCTst, IOPst and IOPnct values by Corvis ST were significantly lower than CCT by Pentacam ([548.23±26.31]μm, IOPg ([15.02±2.72]mmHg and ([16.02±2.56]mmHg) by ORA respectively (t=11.00, 2.919, 6.815, all at P<0.01). Conclusions The corneal deformation parameters by Corvis ST can quantitatively describe corneal biomechanical properties in myopic eyes.Both IOP and the corneal steep curvature of the 3 mm center area (K2) affect the deformation response of cornea.The reliability of Corvis ST in the measurement of CCT and IOP remains to be further studied. Key words: Cornea/physiopathology; Cornea/anatomy h Myopia/physiopathology; Biomechanical phenomena/physiology; Elasticity/physiology; Corneal deformation parameters

Dynamic Scheimpflug-based assessment of keratoconus and the effects of corneal cross-linking.

To evaluate the ability of the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) to distinguish between normal and keratoconic corneas and detect the possible stiffening effect of corneal cross-linking (CXL) in vivo. A retrospective study including 86 eyes of 86 participants (27 patients with untreated keratoconus, 27 patients with CXL-treated keratoconus, and 32 normal patients). The prospective study included 9 keratoconic eyes measured 24 days before and 97 days after CXL. The following parameters from the Corvis ST showed a significant difference between keratoconic and normal eyes: intraocular pressure, corneal thickness, first applanation time, highest concavity (HC) radius, HC deformation amplitude, and HC deflection amplitude (analysis of variance, P < .0001). Receiver operating characteristic curve analysis showed the highest area under the curve for HC deflection amplitude (0.942, P < .0001). Prediction intervals for individual measurements within the two groups overlapped considerably. No significant difference was found between the untreated and CXL-treated keratoconus groups (analysis of variance, P > .05). Measurements performed before and after CXL in the same patients showed significant difference in HC deformation amplitude (P = .018), HC time (P = .018), and second applanation time (P = .027). Although the corneal deformation characteristics differed between groups of keratoconic and normal eyes, this study showed that the standard parameters of the Corvis ST cannot readily be used for diagnosis of keratoconus in the individual patient or to document the effect of CXL in vivo.