August 2015
Volume 56, Issue 9
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Glaucoma  |   August 2015
Corneal Deformation Response in Patients With Primary Open-Angle Glaucoma and in Healthy Subjects Analyzed by Corvis ST
Author Affiliations & Notes
  • Wei Wang
    Zhongshan Ophthalmic Center State Key Laboratory of Ophthalmology, Sun Yat-sen University, Guangzhou, China
  • Shaolin Du
    Zhongshan Ophthalmic Center State Key Laboratory of Ophthalmology, Sun Yat-sen University, Guangzhou, China
  • Xiulan Zhang
    Zhongshan Ophthalmic Center State Key Laboratory of Ophthalmology, Sun Yat-sen University, Guangzhou, China
  • Correspondence: Xiulan Zhang, Clinical Research Center, Zhongshan Ophthalmic Center, State Key Laboratory of Ophthalmology, Sun Yat-sen University, 54 S. Xianlie Road, Guangzhou, China 510060; zhangxl2@mail.sysu.edu.cn
Investigative Ophthalmology & Visual Science August 2015, Vol.56, 5557-5565. doi:10.1167/iovs.15-16926
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      Wei Wang, Shaolin Du, Xiulan Zhang; Corneal Deformation Response in Patients With Primary Open-Angle Glaucoma and in Healthy Subjects Analyzed by Corvis ST. Invest. Ophthalmol. Vis. Sci. 2015;56(9):5557-5565. doi: 10.1167/iovs.15-16926.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: To compare corneal deformation response between patients with primary open-angle glaucoma (POAG) and healthy subjects. A prevalent case-control study was conducted, followed by an integrated meta-analysis.

Methods: Primary open-angle glaucoma was confirmed by presence of glaucomatous optic disc damage with corresponding visual field defect after excluding secondary causes. Age-matched controls were recruited. Corvis ST (CST) was used to measure 10 parameters of corneal deformation response and central corneal thickness (CCT). The association between parameters of deformation response and clinical factors was assessed by the linear regression analyses. Differences in deformation response between POAG and healthy subjects were compared after adjusting for other factors. Eligible studies were identified by a systematic search of the PubMed, ISI Web of Science, and Embase databases; Web sites of professional associations; and the Google Scholar engine.

Results: This study included 37 patients with POAG and 36 healthy controls. Significant associations were found between IOP and the first applanation time (A1T), first applanation velocity (A1V), second applanation time (A2T), and second applanation velocity (A2V) in each group. The deformation amplitude (DA), A1V, and A2T were lower in the POAG group, whereas the A1T, A2V and peak distance (PD) were greater in the POAG group than in the healthy controls (all P < 0.05). Ten separate studies plus the present study, involving 691 patients with POAG and 740 controls, were ultimately meta-analyzed. The significant differences in the DA, A1T, and A2T were further confirmed, with pooled weighted mean difference (WMD) of 0.13 mm (95% CI 0.04–0.23; P = 0.008) for A1T, −0.13 mm (95% CI −0.21 to −0.05; P = 0.001) for DA, and −0.46 ms (95% CI −0.70 to −0.22; P < 0.001) for A2T.

Conclusions: The corneal response parameters provided by CST are informative for the assessment of corneal biomechanics. Patients with POAG showed significantly greater A1T and lower DA and A2T values than healthy controls, indicating a less deformable cornea in POAG patients.

Primary open-angle glaucoma (POAG) is the leading cause of irreversible blindness worldwide.1 Increased IOP is considered the most important risk factor for the presence or progression of POAG. More recently, thin central corneal thickness (CCT) and altered corneal biomechanics were also identified as potential risk factors for POAG and have attracted wide attention. The Early Manifest Glaucoma Trial (EMGT) and the Ocular Hypertension Treatment Study (OHTS) showed that thinner CCT predicted the development of POAG and that the risk of visual field defect increased by 25% and 71% for each 40-μm reduction in CCT. 
Previous evaluations of corneal biomechanics were limited to in vitro studies until the introduction of the Ocular Response Analyzer (ORA) (Reichert, Inc., Depew, NY, USA) in 2005. The ORA evaluates corneal biomechanics in vivo and provides two parameters of corneal deformation response: corneal hysteresis (CH) and corneal hysteresis factor (CHF). Several studies demonstrated a lower CH in various types of glaucoma when compared with normal eyes or eyes with ocular hypertension.27 Recent evidence shows that low CH was also associated with the optic nerve and visual field damage of glaucoma.810 Corneal hysteresis was related to optic nerve head deformation after acute IOP reduction in patients with POAG.11,12 Furthermore, the risk of structural and functional glaucoma progression may be more strongly related to CH than to CCT.13 
A newer device, the Corvis ST (CST; Oculus, Wetzlar, Germany), has recently become available for in vivo assessment of corneal biomechanics. The CST technique records the entire process of the dynamic reaction of the cornea to a fixed air impulse. It is designed for greater accuracy, for provision of repeatable and reproducible results, and for a wide measurement range. Recently, several studies have compared the corneal biomechanics from ORA and CST. Tejwani et al.14 found that CST was statistically significantly different from ORA and CST may be more useful in delineating true biomechanical differences. Bak-Nielsen et al.15 also demonstrated poor correlation between CST parameters and CH/CHF obtained by ORA. However, only a few studies have used CST to compare the corneal deformation response between POAG and healthy subjects. These studies have had small sample sizes and arrived at mixed results. Some researchers16,17 found significant differences in corneal biomechanics by CST, and others18,19 did not. More studies on this issue are therefore warranted. In the present study, we first decided to evaluate the corneal deformation response in POAG patients and healthy subjects and to identify the potential influencing factors. We then sought to conduct a comprehensive meta-analysis to shed additional light on current uncertain claims that corneal deformation response in POAG patients was altered. 
Methods
Subjects and Procedures
This case-control study was approved by the Institutional Review Board of the Zhongshan Ophthalmic Centre and was conducted according to the tenets of the Declaration of Helsinki. Written consent was obtained from all subjects before enrolling. All subjects were sequentially recruited from the Zhongshan Ophthalmic Centre, Sun Yat-sen University, Guangzhou, China. All participants were required to have spherical equivalent and astigmatism less than 2.0 diopters, best-corrected visual acuity (BCVA) of 20/40 or better, clear media, no history of ocular laser or surgical therapy, no history of corneal contact lens wearing, and no history of diabetic mellitus, systemic hypertension, or mental illness. 
Primary open-angle glaucoma was confirmed by a glaucoma expert (XZ) according to the following criteria: (1) history of IOP higher than 21 mm Hg, (2) open angles on gonioscopy, (3) glaucomatous optic disc damage (vertical cup-to-disc ratio > 0.7 and/or interocular asymmetry of cup-to-disc ratio > 0.2 and/or focal rim notching), (4) with corresponding visual field defect (Humphrey Field Analyzer), (5) and exclusion of secondary causes. Intraocular pressure–lowering medication was not excluded in this study. All POAG patients had at least two consecutive visual field tests with reliable results (fixation losses < 20%, false positives < 15%, and/or false negatives ≤ 15%). A visual field defect was defined as two or more contiguous points with a pattern deviation P < 0.01 sensitivity loss, or three or more contiguous points with P < 0.05 sensitivity loss in the superior or inferior arcuate areas, or a 10-dB difference across the nasal horizontal midline at two or more adjacent locations and glaucoma hemifield test results outside normal limits. 
The healthy controls without glaucoma were recruited from hospital staff and relatives of inpatients. Inclusion criteria for controls were IOP lower than 21 mm Hg, normal retinal and optic disc appearance, and free of other ocular or systemic diseases. The controls were age-matched with patients with POAG. All subjects were Han Chinese with a similar ethnic background. All participants underwent the same ocular examinations in both eyes. For patients with bilateral glaucoma and healthy subjects, only data from the right eye were analyzed. Exclusion criteria for all subjects included history of glaucoma or refractive surgery, evidence of ocular disease affecting corneal biomechanics, inability to complete ophthalmic examinations, use of systemic corticosteroids or any intravitreal medications, and poor image quality. 
Ophthalmic Examinations
All subjects received a complete ophthalmic evaluation, which included the measurement of BCVA, slit-lamp biomicroscopy, gonioscopy, IOP measurement (Goldmann applanation tonometry), and fundus examination. The corneal biomechanics (parameters of corneal deformation response) and CCT were determined using the CST. The CST has been described in previous studies.2022 In brief, the CST is equipped with a high-speed Scheimpflug camera (4330 frames per second) that records and displays the entire dynamic deformation response of cornea to a puff of air. The light source was from an ultraviolet-free blue light-emitting diode with 455-nm wavelength. An 8-mm horizontal portion of the cornea was covered and 140 digital frames were obtained in a CST measurement of 31-ms duration. The image resolution was as much as 640 × 480 pixels. The air puff was constant at an internal pump pressure (25 kPa) and time (20 ms). 
A representative process of deformation response and parameters provided by CST is shown in Figure 1. The air pulse first causes the cornea to move inward or flatten (the first applanation, A1). The cornea continues move inward to the highest concavity, and then it rebounds to flatten (the second applanation, A2), and finally assumes its normal convex curvature. The CST records throughout this deformation process and calculates the IOP, CCT, and 10 other biomechanical parameters (Table 1).14,15 
Figure 1
 
A representative process of deformation response and parameters provided by CST. (A) The first applanation (A1). (B) The cornea moves inward to the highest concavity. (C) The second applanation (A2). (D) Corvis ST output.
Figure 1
 
A representative process of deformation response and parameters provided by CST. (A) The first applanation (A1). (B) The cornea moves inward to the highest concavity. (C) The second applanation (A2). (D) Corvis ST output.
Table 1
 
The Corneal Response Parameters Provided by CST14,15
Table 1
 
The Corneal Response Parameters Provided by CST14,15
All CST examinations were conducted by the same operator who was blind to the study protocol. The CST also provides values of IOP, but only the IOP measured by Goldmann applanation tonometry was used for statistical analyses. 
Statistical Analysis
The Shapiro-Wilks test was used to confirm the normality of the continuous variables. The χ2 test was used to compare categorical variables and Student's t-test was used to compare continuous characteristics. The linear regression analysis was used to assess the correlation of corneal response parameters and other factors. Analysis of covariance (ANCOVA) was used to calculate and compare corneal response parameters after adjusting for other factors for the POAG and healthy subjects. 
This meta-analysis was complied with the Meta-Analysis of Observational Studies in Epidemiology (MOOSE) guideline at all stages of the process.23 Studies on corneal deformation response in glaucoma were identified by a systematic search of the PubMed, ISI Web of Science, and Embase databases, without any language restriction, from 2012 to June 10, 2015. Search terms included “Corvis,” “Scheimpflug,” “glaucoma,” “IOP,” and “corneal biomechanical.” Additional studies were identified by searching the Web sites of professional associations (ARVO, American Academy of Ophthalmology [AAO], American Glaucoma Society [AGS], European Glaucoma Society Congress [EGS], World Glaucoma Congress [WGC]) and the Google Scholar engine. The references of relevant reviews and original articles were further hand-reviewed for potential articles. Titles and abstracts were screened to identify potentially relevant studies by two reviewers independently. If the eligibility of an article was uncertain, the full text was then evaluated. 
Studies were included if they fulfilled the following criteria: the study should be cross-sectional or case-control design, corneal biomechanical parameters were measured by CST, the study contains sufficient information to calculate differences in deformation response between patients with POAG and controls, and outcomes included at least 1 of the above 10 parameters. Reviews, letters, case reports, not human studies, corneal biomechanics not assessed by CST, and studies without sufficient information were excluded. In studies of the same population, only the latest or the most complete studies were included. When possible, the maximally adjusted mean difference in deformation response parameters and its 95% confidential interval (CI) were extracted. Results that were more conservative were obtained by using the random effects model to calculate pooled weighted mean differences (WMDs). Statistical heterogeneity between studies was quantified with χ2 test and I2 statistics. For the χ2 test, a P value less than 0.10 indicates significant heterogeneity; for the I2 statistic, values of 25%, 50%, and 75% represent mild, moderate, and severe heterogeneity, respectively.24 Sensitivity analyses were performed by assessing the influences of individual studies on the pooled results. Funnel plots, Begg's test, and Egger's test were used to evaluate potential publication bias. All statistical analyses were performed by Stata SE 12.0 (StataCorp, College Station, TX, USA) and the level of significance was set at 0.05, two sided, except when otherwise specified. 
Results
Demographic and Clinical Features of the Subjects
The study included 37 unrelated patients (37 eyes) with POAG and 36 healthy subjects (36 eyes) who fulfilled the inclusion criteria. Table 2 presents the demographic and clinical characteristics of the subjects. The mean ages of the patients and the healthy controls were 51.47 ± 18.84 and 52.81 ± 13.24 years, respectively (P = 0.129). The POAG patients and healthy controls had similar sex distribution and CCT. However, as expected, the POAG patients had greater IOP than the healthy controls (23.15 vs. 14.44 mm Hg, P < 0.001). 
Table 2
 
Demographic and Clinical Characteristics of the Participants
Table 2
 
Demographic and Clinical Characteristics of the Participants
Factors Associated With Corneal Response Parameters
Linear regression analyses were performed to assess the correlations between corneal response parameters and potential factors. The regression results are summarized in Table 3. Sex was not significantly associated with any 10 parameters. Only one parameter (applanation 2 length [A2L]) showed a significant correlation with age in healthy controls. The deformation amplitude (DA) and peak distance (PD) showed significant associations with IOP in all eyes and nonsignificant associations with IOP in healthy controls. The applanation 1 length (A1L) was correlated significantly with IOP in healthy controls and nonsignificantly with IOP in POAG patients. The applanation 1 time (A1T), applanation 1 velocity (A1V), applanation 2 time (A2T), and applanation 2 velocity (A2V) were significantly associated with IOP in healthy controls and POAG patients. However, no significant correlations were noted between A2L, time to highest concavity (HCT), and central curvature radius (CCR) with IOP in any groups. In all eyes and in POAG patients, PD was significantly correlated with CCT. No associations between other parameters and CCT were evident in healthy controls and POAG patients. 
Table 3
 
Linear Regression Analyses of Corneal Response Parameters and Clinical Factors
Table 3
 
Linear Regression Analyses of Corneal Response Parameters and Clinical Factors
Corneal Deformation Compared Between POAG and Controls
Analysis of covariance was performed to account for IOP. Age was also included in all analyses (except for HCT and CCR) because previous studies demonstrated an effect of age on corneal biomechanics, though only one parameter (A2L) was statistically associated with age in this study. Table 4 shows the corneal deformation parameters after adjusting for other factors, with the exception of HCT and CCR. Significant differences in 6 of 10 corneal response parameters were observed between POAG and healthy controls. The DA, A1V, and A2T were lower in the POAG group, whereas A1T, A2V, and PD were greater in the POAG group than in the healthy controls (all P < 0.05). 
Table 4
 
Corneal Response Parameters in POAG and Healthy Subjects After Adjusting Other Factors
Table 4
 
Corneal Response Parameters in POAG and Healthy Subjects After Adjusting Other Factors
Literature Search
To obtain evidence with greater robustness and objectivity, a comprehensive meta-analysis was performed. The study selection process is summarized in Figure 2. The initial search identified 143 potential eligible studies. After exclusion of duplicates, 106 articles underwent titles and abstracts screening. Among of them, 93 articles were removed for the following reasons: irrelevant topic, not CST, review, case report, technique evaluation, not glaucoma patients. Of the 13 full-text studies that were evaluated, 7 studies with no data on dynamic parameters were excluded. Four additional studies (Refs. 25–27, Hong K, et al. IOVS 2014;55:ARVO E-Abstract 3725) were identified by searching the Web sites of professional associations. Thus, 10 studies included 6 published full-text studies1619,28,29 and 4 meeting abstracts (Refs. 25–27, Hong K, et al. IOVS 2014;55:ARVO E-Abstract 3725) were used in the meta-analysis. 
Figure 2
 
Diagram of the process of literature search.
Figure 2
 
Diagram of the process of literature search.
Characteristics of the Studies Included in the Meta-Analysis
Table 5 summarizes the characteristics of the studies that reported differences in corneal response between glaucoma and controls using CST. Of these 10 previous studies, 5 were conducted on Chinese subjects, 1 on Korean subjects, and 4 on Caucasian subjects. Sample size ranged from 56 to 217 participants per study. Six studies matched cases and controls for age, and/or IOP, and/or CCT. Three studies16,17,30 reported adjusted differences in corneal response parameters between patients and controls, whereas the other seven studies only provided crude data. These 10 separate studies plus the present study, encompassing a total of 691 patients with POAG and 740 controls, were finally meta-analyzed. 
Table 5
 
Characteristics of the Studies by CST Included in the Meta-analysis
Table 5
 
Characteristics of the Studies by CST Included in the Meta-analysis
Meta-Analysis Results
Table 6 presents the pooled differences of corneal response between POAG and healthy subjects. Differences in 3 of 10 corneal response parameters between patients and controls remained significant after combining all the qualified studies. Patients with POAG showed greater A1T and lower DA and A2T, with pooled WMDs of 0.13 mm (95% CI 0.04–0.23; P = 0.008) for A1T, −0.13 mm (95% CI −0.21 to −0.05; P = 0.001) for DA, and −0.46 ms (95% CI −0.70 to −0.22; P < 0.001) for A2T. Severe statistical heterogeneities were observed. The combined results were consistent with our cross-sectional study, supporting the findings that corneal mechanics differ between POAG and healthy subjects. No single study changed the pooled results in sensitivity analyses. The funnel plot detected no evidence of publication bias, as further confirmed by Begg's tests and Egger's tests. 
Table 6
 
Pooled Differences of Corneal Response Between POAG and Healthy Subjects
Table 6
 
Pooled Differences of Corneal Response Between POAG and Healthy Subjects
Discussion
Despite great efforts, the role of corneal biomechanics in POAG has not been fully elucidated because CCT and CH/CHF may not explain all of the corneal biomechanical alterations.13 The recently available CST, which combines a pneumotonometer with an ultrahigh-speed Scheimpflug camera, captures the entire corneal depression and reformation cycle with 4330 frames per second. Theoretically, CST has advantages over another instruments (e.g., ORA). Several studies have demonstrated that CST results differed completely from those obtained by ORA and that CST may be more useful in delineating true biomechanical differences between the eyes, even though both these devices detect corneal response in vivo by a fixed air pulse.15,19,30 The CST automatically calculates the time and length of the cornea deformations and the instantaneous speed of corneal movement at the two applanation states. A less deformable cornea is thought to reach A1 slower (with a longer A1T, A1L, and smaller A1V), show a smaller concavity (with smaller DA and higher PD and CCR), and reach A2 faster (with shorter A2T, longer A2L, and higher A2V).17 Thus, data obtained from CST may expand our understanding of corneal biomechanics in POAG. 
Our case-control study showed that POAG patients had smaller A1V, DA, and A2T, and greater A1T, A2V, and PD, which indicated that the corneas in POAG patients were less deformable than those in healthy controls. The identification of the 10 previous reported studies that assessed corneal response differences by CST between patients with POAG and controls, obtained by our systematic review, allowed us to combine our data with the data from these studies due to their similar designs and methods. The significant differences in DA, A1T, and A2T were further confirmed in this meta-analysis, indicating the robustness of our findings. These parameters may be markers of ocular structural weakness and could be associated with increased susceptibility to glaucoma. To the best of our knowledge, this is the first meta-analysis on this topic. 
Few data on corneal biomechanics by CST are available currently because the instrument is not yet in wide use. Salvetat et al.17 found that glaucoma patients showed significantly higher A1T and smaller A1V, A2T, A2V, and DA than controls in a prospective randomized study. Tian et al.16 demonstrated lower A1V, A2T, PD, and DA in eyes with POAG than in normal eyes. However, no significant differences in any parameters between POAG and controls were observed in study by Leung and colleagues.19 Another prospective study with 60 POAG patients and 61 healthy controls by Lee et al.29 showed lower HCT in POAG patients than in healthy controls (16.75 ± 0.08 ms versus 17.05 ± 0.07 ms, P = 0.001), which indicated a weaker and more deformable cornea in POAG eyes than in normal eyes. The findings of our study were essentially consistent with the studies by Salvetat et al.17 and Tian et al.16 The discrepancy among the previous studies may be due to the variations in ethnicity, sample size, IOP, or numbers of adjusting factors. 
The present study has important strengths that merit adequate consideration. It represents the first synthesis exploring the differences in corneal biomechanics by CST between POAG and healthy subjects. The results of the present case-control study were also in accordance with the corresponding meta-analysis. Furthermore, our findings are less prone to selection bias, as evident by the low possibility of publication bias. 
The corneal deformation following an air puff may be influenced by several demographic and clinical factors. A significant correlation was found between IOP and CST data in previous studies.16,17,21,31,32 In the present study, A1T, A1V, A2T, and A2V were significantly related to the IOP in both POAG and healthy controls. The DA and PD were inversely related to the IOP in all eyes and POAG eyes, which suggested that the corneal deformability decreased with increasing IOP.17 Age has been reported to affect corneal biomechanical properties, with corneal stiffness increasing with age.33,34 However, all corneal response parameters, except A2L, showed nonsignificant correlations with age, in agreement with the studies by Pedersen et al.,35 Nemeth et al.,21 and Ali et al.33 We, as well as Valbon et al.,20 consistently observed no relationship between the studied parameters and sex. Perez-Rico et al.36 demonstrated that diabetes mellitus affects CST measurement process. In this study, subjects with diabetes mellitus were excluded. Lanza et al.37 examined the association among CCT, corneal volume, corneal curvature, and corneal deformation parameters measured by CST and none of them were statistically significant. The most interesting observation was that no correlation was found between age, sex, IOP, CCT with A2L, HCT and CCR. These parameters may be worth studying further as independent biomarkers for ocular diseases. Studies have reported that the corneal deformation parameters are also influenced by corneal hydration, stiffness, the boundary condition related to the sclera, and the ocular muscles.38 Thus, further studies are warranted to determine the relationship between these factors and CST parameters. 
Several limitations apply to the present study. First, no account was taken of possible influences of duration of disease or history of medical treatment on corneal response parameters. This is a major limitation of this study and meta-analysis. Prior study has demonstrated that baseline CH measured by ORA is independently associated with the magnitude of IOP reduction with topical prostaglandin therapy.39 However, in studies by CST, Leung et al.19 reported that use of topical IOP-lowering medicines and use of topical prostaglandin analogues have no effect on the measurement of DA. Recently, Lee et al.26 found that antiglaucomatous agents were not likely to influence corneal biomechanics. Thus, more studies are warranted to clarify the influence of medication on corneal biomechanics. Second, the small sample size is another major limitation. However, the meta-analysis included 691 patients with POAG and 740 controls that largely enhanced the statistical power, and the findings of our primary study were confirmed by the meta-analysis. Third, an association between corneal curvature with all corneal response parameters has been reported.21 However, this factor was not adjusted in most other studies, including ours. Furthermore, it will be more informative if future studies also can include more systemic/ocular parameters of the participants (e.g., HbA1c, diabetic status, hypertension status, spherical equivalent). Fourth, the prevalent case-control design does not allow identification of a cause-effect relationship between CST parameters and presence of POAG. Neither the mean defect in the visual field nor the retinal nerve fiber layer thickness were evaluated, so the association between corneal response parameters and glaucomatous severity is unclear. We would like to examine these issues in further studies. Last, the CST parameters were obtained in a single day, but CH and CHF show significant diurnal variation.34 CST parameters also may have diurnal variation and this should be determined in the near future. 
In conclusion, the corneal response parameters provided by CST are informative for the assessment of corneal biomechanics. Patients with POAG showed significantly greater A1T and lower DA and A2T than healthy controls, which indicated that corneas in POAG patients were less deformable. The findings are supported by a meta-analysis. The role of corneal biomechanics in POAG deserves more clinical attention and further studies using CST are warranted to assess its usefulness. 
Acknowledgments
Supported in part by the Science and Technology Program of Guangdong Province, China (2013B020400003), and the Science and Technology Program of Guangzhou, China (15570001). 
Disclosure: W. Wang, None; S. Du, None; X. Zhang, None 
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Figure 1
 
A representative process of deformation response and parameters provided by CST. (A) The first applanation (A1). (B) The cornea moves inward to the highest concavity. (C) The second applanation (A2). (D) Corvis ST output.
Figure 1
 
A representative process of deformation response and parameters provided by CST. (A) The first applanation (A1). (B) The cornea moves inward to the highest concavity. (C) The second applanation (A2). (D) Corvis ST output.
Figure 2
 
Diagram of the process of literature search.
Figure 2
 
Diagram of the process of literature search.
Table 1
 
The Corneal Response Parameters Provided by CST14,15
Table 1
 
The Corneal Response Parameters Provided by CST14,15
Table 2
 
Demographic and Clinical Characteristics of the Participants
Table 2
 
Demographic and Clinical Characteristics of the Participants
Table 3
 
Linear Regression Analyses of Corneal Response Parameters and Clinical Factors
Table 3
 
Linear Regression Analyses of Corneal Response Parameters and Clinical Factors
Table 4
 
Corneal Response Parameters in POAG and Healthy Subjects After Adjusting Other Factors
Table 4
 
Corneal Response Parameters in POAG and Healthy Subjects After Adjusting Other Factors
Table 5
 
Characteristics of the Studies by CST Included in the Meta-analysis
Table 5
 
Characteristics of the Studies by CST Included in the Meta-analysis
Table 6
 
Pooled Differences of Corneal Response Between POAG and Healthy Subjects
Table 6
 
Pooled Differences of Corneal Response Between POAG and Healthy Subjects
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