Comparison of Corneal Biomechanics Between Low and High Myopic Eyes-A Meta-analysis

Corneal Biomechanical Characteristics in Myopes and Emmetropes Measured by Corvis ST: A Meta-Analysis

PURPOSE

To comprehensively identify the corneal biomechanical differences measured by Corvis ST between different degrees of myopia and emmetropia.

DESIGN

Systematic review and meta-analysis.

METHODS

Electronic databases, including PubMed, Embase, and Web of Science, were systematically searched for studies comparing the corneal biomechanics among various degrees of myopes and emmetropes using Corvis ST. The weighted mean differences and 95% confidence intervals were calculated. Meta-analysis was performed in high and nonhigh myopes and in myopes and emmetropes, respectively.

RESULTS

Eleven studies were included in this study. The meta-analysis among myopes and emmetropes included 1947 myopes and 621 emmetropes, and 443 high myopes and 449 nonhigh myopes were included in the meta-analysis among high and nonhigh myopia. Myopes showed the cornea with significantly longer time at the first applanation (A1t) and lower length at the second applanation (A2L) than emmetropes. High myopes showed significantly greater A1t, velocity at the second applanation (A2v), deformation amplitude at the highest concavity (HC-DA), and peak distance at the highest concavity (HC-PD) and decreased time at the second applanation (A2t) and radius of the highest concavity (HC-R).

CONCLUSIONS

Corneal biomechanics is different in myopia, especially in high myopia. Compared with nonhigh myopes, the corneas of high myopes deformed slower during the first applanation, faster during the second applanation, and showed greater deformation amplitude, indicating greater elasticity and viscidity.

The biomechanical proteins different between low myopic corneas and moderate to high myopic corneas in human

PURPOSE

To explore the biomechanical proteins different between low myopic corneas and moderate to high myopic corneas.

METHODS

A total of 27 myopic corneas were used for the Tandem Mass Tag (TMT) proteomics analysis. Differentially expressed proteins (DEPs) were clustered with fold changes > 1.20 or < 0.83 and p < 0.05. Proteins and Proteins Interactions (PPIs) were conducted to find hub proteins; Uniprot database was to screen proteins with biomechanical functions, and Parallel Reaction Monitoring (PRM) was performed to verify the TMT results. Pearson analysis was used to reveal the correlations between myopic degrees and biomechanical proteins. The Immunofluorescence (IF) staining was used to observe the protein distributions.

RESULTS

In total, 34 DEPs were observed between moderate myopic corneas and low myopic corneas; 103 DEPs were observed between high myopic corneas and low myopic corneas, 20 proteins overlapped. The PPIs analysis showed keratin 2, keratins 10 and PRSS1 were hub proteins. The Uniprot function analysis suggested keratin 2 and keratin 10 exhibited biomechanical functions. The PRM demonstrated keratin 2 and keratin 10 levels were significantly lower in moderate and high myopic corneas, which was consistent with the TMT proteomics results. IF staining also demonstrated keratin 2 and keratin 10 were less distributed in moderate and high myopic corneas than in low myopic corneas.

CONCLUSIONS

The levels of biomechanical proteins keratin 2 and keratin 10 are significantly lower in moderate and high myopic corneas than in low myopic corneas.

Corneal stress‒strain index in relation to retinal nerve fibre layer thickness among healthy young adults

BACKGROUND/OBJECTIVES

To determine the relationship between corneal stress-strain index (SSI) and retinal nerve fibre layer (RNFL) thickness.

SUBJECTS/METHODS

1645 healthy university students from a university-based study contributed to the analysis. The RNFL thickness was measured by high-definition optical coherence tomography (HD-OCT), axial length (AL) was measured by IOL Master, and corneal biomechanics including SSI, biomechanical corrected intraocular pressure (bIOP), and central corneal thickness (CCT) were measured by Corvis ST. Multivariate linear regression was performed to evaluate the relationship between the SSI and RNFL thickness after adjusting for potential covariates.

RESULTS

The mean age of the participants was 19.0 ± 0.9 years, and 1132 (68.8%) were women. Lower SSI was significantly associated with thinner RNFL thickness ( β =8.601, 95% confidence interval [CI] 2.999-14.203, P  = 0.003) after adjusting for age, CCT, bIOP, and AL. No significant association between SSI and RNFL was found in men, while the association was significant in women in the fully adjusted model. The association was significant in the nonhigh myopic group ( P for trend = 0.021) but not in the highly myopic group. Eyes with greater bIOP and lower SSI had significantly thinner RNFL thickness.

CONCLUSIONS

Eyes with lower SSI had thinner RNFL thickness after adjusting for potential covariates, especially those with higher bIOP. Our findings add novel evidence of the relationship between corneal biomechanics and retinal ganglion cell damage.

Comparative analysis of corneal parameters in simple myopic anisometropia using Scheimpflug technology

Purpose

This study aims to investigate the differences in binocular corneal parameters and their interrelation with binocular biometric parameters asymmetry in patients with simple myopic anisometropia, thereby elucidating the influence of myopia process on various corneal parameters.

Methods

In this cross-sectional study, 65 patients with anisometropia in monocular myopia were included. They were divided into low anisometropia group: 3.00D<Δ spherical equivalent (SE)≤-1.00D (Δ represents the difference between the two eyes, i.e., myopic data minus emmetropic data) and high anisometropia group: ΔSE ≤ -3.00D. Corneal and ocular biometric parameters were measured using Pentacam, Corvis ST, and IOL Master 700. Statistical analyses focused on the binocular corneal parameters asymmetry, using the contralateral emmetropia as a control.

Results

The mean age of participants was 18.5 ± 1.3 years, with the average SE for myopia and emmetropia being -2.93 ± 1.09D and -0.16 ± 0.41D, respectively. The central corneal thickness (CCT), flat keratometry (Kf), keratometry astigmatism (Ka), total corneal aberration (6 mm) (TOA), surface variance index (ISV), vertical asymmetry index (IVA), stress-strain index (SSI), and first applanation stiffness parameter (SPA1) and ambrosia relational thickness-horizontal (ARTh) showed significant differences between anisometropic fellow eyes (p < 0.05). There were significant differences in ΔIVA, Δ the difference between the mean refractive power of the inferior and superior corneas (I-S), Δ deviation value of Belin/Ambrósio enhanced ectasia display (BAD-D), Δ deformation amplitude ratio max (2 mm) (DAR)and Δ tomographic biomechanical index (TBI) (p < 0.05) in two groups. Asymmetry of corneal parameters was correlated with asymmetry of ocular biometric parameters. Anisometropia (ΔSE) was positively correlated with ΔIVA (r = 0.255, p = 0.040), ΔBAD-D (r = 0.360, p = 0.006), and ΔSSI (r = 0.276, p = 0.039) and negatively correlated with ΔDAR (r = -0.329, p = 0.013) in multiple regression analysis. Δ mean keratometry (Km), Δ anterior chamber depth (ACD), and Δ biomechanically corrected intraocular pressure (bIOP) were also associated with binocular corneal differences.

Conclusion

Compared to contralateral emmetropia, myopic eyes have thinner corneas and smaller corneal astigmatism. Myopic corneas exhibit relatively more regular surface morphology but are more susceptible to deformation and possess marginally inferior biomechanical properties. In addition, there is a certain correlation between anisometropia and corneal parameter asymmetry, which would be instrumental in predicting the development of myopia.

Refractive associations with corneal biomechanical properties among young adults: a population-based Corvis ST study

PURPOSE

To assess the associations of corneal biomechanical properties as measured by the Corvis ST with refractive errors and ocular biometry in an unselected sample of young adults.

METHODS

A total of 1645 healthy university students underwent corneal biomechanical parameters measurement by the Corvis ST. The refractive status of the participants was measured using an autorefractor without cycloplegia. Ocular biometric parameters were measured using the IOL Master.

RESULTS

After adjusting for the effect of age, sex, biomechanical-corrected intraocular pressure and central corneal thickness, axial length was significantly associated with A1 velocity (A1v, β = -10.47), A2 velocity (A2v, β = 4.66), A2 deflection amplitude (A2DeflA, β = -6.02), HC deflection amplitude (HC-DeflA, β = 5.95), HC peak distance (HC-PD, β = 2.57), deformation amplitude ratio max (DA Rmax, β = -0.36), Ambrósio's relational thickness to the horizontal profile (ARTh, β = 0.002). For axial length / corneal radius ratio, only A1v (β = -2.01), A1 deflection amplitude (A1DeflA, β = 2.30), HC-DeflA (β = 1.49), HC-PD (β = -0.21), DA Rmax (β = 0.07), stress-strain index (SSI, β = -0.29), ARTh (β < 0.001) were significant associates. A1v (β = 23.18), HC-DeflA (β = -15.36), HC-PD (β = 1.27), DA Rmax (β = -0.66), SSI (β = 3.53), ARTh (β = -0.02) were significantly associated with spherical equivalent.

CONCLUSION

Myopic eyes were more likely to have more deformable corneas and corneas in high myopia were easier to deform and were even softer compared with those in the mild/moderate myopia.

Exploration of the pathophysiology of high myopia via proteomic profiling of human corneal stromal lenticules

This study aimed to investigate the underlying pathophysiology of high myopia by analyzing the proteome of human corneal stromal lenticule samples obtained through small incision lenticule extraction (SMILE). A total of thirty-two patients who underwent SMILE were included in the study. Label-free quantitative proteomic analysis was performed on corneal stromal lenticule samples, equally representing high myopia (n = 10) and low myopia (n = 10) groups. The identified and profiled lenticule proteomes were analyzed using in silico tools to explore biological characteristics of differentially expressed proteins (DEPs). Additionally, LASSO regression and random forest model were employed to identify key proteins associated with the pathophysiology of high myopia. The DEPs were found to be closely linked to immune activation, extracellular matrix, and cell adhesion-related pathways according to gene ontology analysis. Specifically, decreased expression of COL1A1 and increased expression of CDH11 were associated with the pathogenesis of high myopia and validated by western blotting (n = 6) and quantitative real time polymerase chain reaction (n = 6). Overall, this study provides evidence that COL1A1 and CDH11 may contribute to the pathophysiology of high myopia based on comparative proteomic profiling of human corneal stromal lenticules obtained through SMILE.

Comparisons of the protein expressions between high myopia and moderate myopia on the anterior corneal stroma in human

PURPOSE

To investigate the differentially expressed proteins (DEP) between high myopia and moderate myopia on the anterior corneal stroma.

METHODS

Tandem mass tag (TMT) quantitative proteomics was utilized to reveal proteins. DEPs were screened by the multiple change of more than 1.2 times or less than 0.83 and the P value < 0.05. The DEPs were functional annotated by Gene Ontology (GO) terms. Proteins and protein interaction (PPI) networks were conducted with String online tool. Parallel reaction monitoring (PRM) data processing was used to verify the TMT proteomics results.

RESULTS

There are 36 DEPs between high myopia and moderate myopia on the anterior corneal stroma, of which 11 proteins are upregulated, 25 proteins are downregulated. The GO analysis demonstrated keratinocyte migration and structural constituent of cytoskeleton that are significantly changed with most of the proteins decreased in high myopic corneas. Keratin 16 (KRT16) and erythrocyte membrane protein band 4.1-like protein 4B are the only two proteins involved in both functions. The PPI analysis showed keratin type II cytoskeletal 6A (KRT6A) and KRT16 that have strong connections. Immunoglobulin lambda variable 8-61(IGLV8-61) and nicotinamide phosphoribosyl transferase (NAMPT) have consistent results with the TMT.

CONCLUSIONS

The high myopic corneas have 36 DEPs compared to the moderate myopic corneas on the anterior corneal stroma. Keratinocyte migrations and structural constituent of cytoskeleton are weakened in high myopic corneas, which may partly account for the lower corneal biomechanics in high myopic eyes. The lower expressed KRT16 plays important roles in high myopic corneas.

Corneal metabolic biomarkers for moderate and high myopia in human

This study aimed to identify the corneal metabolic biomarkers for moderate and high myopia in human. We enrolled 221 eyes from 221 subjects with myopia to perform the femtosecond laser small incision lenticule extraction (SMILE) surgery. Among these, 71 eyes of 71 subjects were enrolled in the low myopic group, 75 eyes of 75 subjects in the moderate myopic group and 75 eyes of 75 subjects in the high myopic group. The untargeted metabolomics analysis was performed to analyze the corneal tissues extracted during the SMILE surgery using an ultra-high-performance liquid chromatography (UHPLC) coupled to a quadrupole time-of-flight (Q-TOF) mass spectrometry (MS). The one-way analysis of variance (ANOVA) was used to identify the different metabolites among the three myopic groups, the orthogonal partial least-squares discriminant analysis (OPLS-DA) model was used to reveal the different metabolites between moderate myopia and low myopia, and between high myopia and low myopia. The Venn gram was used to find the overlapped metabolites of the three datasets of the different metabolites. The stepwise multiple linear regression analysis was used to determine the metabolic molecules associated with manifest refractive spherical equivalents (MRSE). The Receiver Operating Characteristics (ROC) analysis was performed to reveal the corneal biomarkers for moderate and high myopia. The hub biomarker was further selected by the networks among different metabolites created by the Cytoscape software. A total of 1594 metabolites were identified in myopic corneas. 321 metabolites were different among the three myopic groups, 106 metabolites were different between high myopic corneas and low myopic corneas, 104 metabolites were different between moderate myopic corneas and low myopic corneas, and 30 metabolic molecules overlapped among the three datasets. The multivariate linear regression analysis revealed the myopic degree was significantly influenced by the corneal levels of azelaic acid, arginine-proline (Arg-Pro), 1-stearoyl-2-myristoyl-sn-glycero-3-phosphocholine, and hypoxanthine. The ROC curve analysis showed that azelaic acid, Arg-Pro and hypoxanthine were effective in discriminating low myopia from moderate to high myopia with the area under the curve (AUC) values as 0.982, 0.991 and 0.982 for azelaic acid, Arg-Pro and hypoxanthine respectively. The network analysis suggested that Arg-Pro had the maximum connections among these three biomarkers. Thus, this study identified azelaic acid, Arg-Pro and hypoxanthine as corneal biomarkers to discriminate low myopia from moderate to high myopia, with Arg-Pro serving as the hub biomarker for moderate and high myopia.

Addressing Glaucoma in Myopic Eyes: Diagnostic and Surgical Challenges

Epidemiological and genetic studies provide strong evidence supporting an association between myopia and glaucoma. The accurate detection of glaucoma in myopic eyes, especially those with high myopia, remains clinically challenging due to characteristic morphologic features of the myopic optic nerve in addition to limitations of current optic nerve imaging modalities. Distinguishing glaucoma from myopia is further complicated by overlapping perimetric findings. Therefore, longitudinal follow-up is essential to differentiate progressive structural and functional abnormalities indicative of glaucoma from defects that may result from myopia alone. Highly myopic eyes are at increased risk of complications from traditional incisional glaucoma surgery and may benefit from newer microinvasive glaucoma surgeries in select cases.

Corneal Biomechanical Properties Demonstrate Anisotropy and Correlate With Axial Length in Myopic Eyes

Purpose

The purpose of this study was to investigate the ex vivo and in vivo biomechanical characteristic of cornea in myopic eyes.

Methods

Fifty-one corneal stromal lenticules were obtained from myopic eyes during the SMILE procedure and were tested by a biaxial tensile system within 24 hours postoperatively. The material properties of the lenticules were described using stress-strain curves and were compared among axial length (AL) <26 mm and AL ≥ 26 mm group. Pre-operative stress-strain index (SSI) parameters were used to evaluate the biomechanical properties of the cornea in vivo.

Results

Compared with AL < 26 mm, the tangent modulus significantly decreased in horizontal and vertical directions when AL ≥ 26 mm (P < 0.05); SSI also significantly decreased when AL ≥ 26 mm (P < 0.05). Anisotropic parameter is positively correlated with AL (r = 0.307, P < 0.05). Compared with AL < 26 mm, anisotropic parameter significantly increased when AL ≥ 26 mm (P < 0.05). SSI was negatively correlated with AL (r = -0.380, P < 0.05) in the AL < 26 mm group but not in the AL ≥ 26 mm group (P > 0.05). Compared with 26 mm ≤ AL < 27 mm group, the tangent modulus significantly decreased in the horizontal direction (P < 0.05) but not in the vertical direction when 27 mm ≤ AL < 28 mm (P > 0.05).

Conclusions

The biomechanical properties of cornea decreased with the increase of AL. Tangent modulus significantly decreased in the horizontal direction compared with vertical direction. AL should be taken into account during calculation of corneal biomechanical parameters in order to improve validity.

Comparison of Conjunctival Sac Microbiome between Low and High Myopic Eyes

Microbial communities played a vital role in maintaining homeostasis of ocular surface. However, no studies explored the myopia-associated conjunctiva microbiota changes until now. In this study, conjunctival sac swab specimens were collected from 12 eyes of low myopia (LM), and 14 eyes of high myopia (HM) patients. The V3-V4 region of the 16S rRNA gene was amplified and then sequenced. Statistical analysis was performed to investigate differences in the taxonomy and diversity between two groups. Compared to LM, higher Ocular Surface Disease Index (OSDI) scores were observed in HM group. The Shannon index of the HM was lower than that of the LM group (P = 0.017). Principle coordinate analysis and Partial Least Squares Discrimination Analysis showed distinct microbiome composition between two groups. At the phylum level, there were higher relative abundances of Proteobacteria (68.27% vs 38.51%) and lower abundances of Actinobacteria (3.71% vs 9.19%) in HM, compared to LM group (P = 0.031, 0.010, respectively). At the genus level, the abundances of Acinetobacter in HM (18.16%) were significantly higher than the LM (6.52%) group (P = 0.011). Actinobacteria levels were negatively correlated with the myopic spherical equivalent and OSDI scores. Moreover, positive correlations were found between Proteobacteria levels and OSDI scores, Acinetobacter levels were positively correlated with myopic spherical equivalent and OSDI scores. In conclusion, HM Patients have bacterial microbiota imbalance in the conjunctival sac, compared with LM patients. Proteobacteria, Actinobacteria, Acinetobacter may play roles in the HM associated ocular surface irritation.

In Vivo Biomechanical Measurements of the Cornea

In early corneal examinations, the relationships between the morphological and biomechanical features of the cornea were unclear. Although consistent links have been demonstrated between the two in certain cases, these are not valid in many diseased states. An accurate assessment of the corneal biomechanical properties is essential for understanding the condition of the cornea. Studies on corneal biomechanics in vivo suggest that clinical problems such as refractive surgery and ectatic corneal disease are closely related to changes in biomechanical parameters. Current techniques are available to assess the mechanical characteristics of the cornea in vivo. Accordingly, various attempts have been expended to obtain the relevant mechanical parameters from different perspectives, using the air-puff method, ultrasound, optical techniques, and finite element analyses. However, a measurement technique that can comprehensively reflect the full mechanical characteristics of the cornea (gold standard) has not yet been developed. We review herein the in vivo measurement techniques used to assess corneal biomechanics, and discuss their advantages and limitations to provide a comprehensive introduction to the current state of technical development to support more accurate clinical decisions.

Mapping Pulsatile Optic Nerve Head Deformation Using OCT

OBJECTIVE

To develop a noninvasive technique to quantitatively assess the pulsatile deformation due to cardiac contractions of the optic nerve head (ONH).

DESIGN

Evaluation of a diagnostic test or technology.

PARTICIPANTS

Healthy subjects with no history of refractive surgery, divided into 2 cohorts on the basis of their axial length (AL).

METHODS

We present a noninvasive technique to quantitatively assess the pulsatile deformation of the ONH tissue by combining high-frequency OCT imaging and widely available image processing algorithms. We performed a thorough validation of the approach, numerically and experimentally, evaluating the sensitivity of the method to artificially induced deformation and its robustness to different noise levels. We performed deformation measurements in cohorts of healthy (n = 9) and myopic (n = 5) subjects in different physiological strain conditions by calculating the amplitude of tissue displacement in both the primary position and abduction. The head rotation was measured using a goniometer. During imaging in abduction, the head was rotated 40° ± 3°, and subjects were instructed to direct their gaze toward the OCT visual target.

MAIN OUTCOME MEASURES

Pulsatile tissue displacement maps.

RESULTS

The robustness of the method was assessed using artificial deformations and increasing noise levels. The results show acceptable absolute errors before the noise simulations grossly exaggerate image degradation. For the group of subjects with AL of < 25 mm (n = 9), the median pulsatile displacement of the ONH was 7.8 ± 1.3 μm in the primary position and 8.9 ± 1.2 μm in abduction. The Wilcoxon test showed a significant difference (P ≤ 0.005) between the 2 paired measures. Reproducibility was tested in 2 different sessions in 5 different subjects with the same intraocular pressure, and an intraclass correlation coefficient of 0.99 was obtained (P < 0.005).

CONCLUSIONS

The computational pipeline demonstrated good reproducibility and had the capacity to accurately map the pulsatile deformation of the optic nerve. In a clinical setting, we detected physiological changes in normal subjects supporting its translation potential as a novel biomarker for the diagnosis and progression of optic nerve diseases.

Unraveling the mechanobiology of cornea: From bench side to the clinic

The cornea is a transparent, dome-shaped structure on the front part of the eye that serves as a major optic element and a protector from the external environment. Recent evidence shows aberrant alterations of the corneal mechano-environment in development and progression of various corneal diseases. It is, thus, critical to understand how corneal cells sense and respond to mechanical signals in physiological and pathological conditions. In this review, we summarize the corneal mechano-environment and discuss the impact of these mechanical cues on cellular functions from the bench side (in a laboratory research setting). From a clinical perspective, we comprehensively review the mechanical changes of corneal tissue in several cornea-related diseases, including keratoconus, myopia, and keratectasia, following refractive surgery. The findings from the bench side and clinic underscore the involvement of mechanical cues in corneal disorders, which may open a new avenue for development of novel therapeutic strategies by targeting corneal mechanics.

Associations between anterior segment biometry and high axial myopia in 3438 cataractous eyes in the Chinese population

Background

To investigate the associations between anterior segment biometry and high axial myopia in cataractous eyes in the Chinese population.

Methods

Data on 3438 eyes from 3438 subjects were analyzed in this cross-sectional study. Anterior segment biometry, axial length measurements, and intraocular pressure evaluation were implemented using an Oculus Pentacam HR, a Zeiss IOLMaster 500, and a Nidek TonoRef II, respectively. A multivariate-adjusted logistic model and a multivariate-adjusted linear model were used for statistical analysis.

Results

The mean age of the subjects was 62.2 ± 10.6 years, and 56.4% were female. There were 2665 subjects with high axial myopia (axial length, ≥26.50 mm) and 773 without (axial length, < 26.50 mm). The characteristics independently associated with high axial myopia included lower total corneal refractive power, a more negative Q value, greater total corneal astigmatism, greater white-to-white corneal diameter, greater anterior chamber depth, and higher intraocular pressure (all P <  0.05). In addition, greater axial length correlated with a thicker temporal cornea and a thinner nasal cornea (both P <  0.001).

Conclusions

For cataractous eyes, high axial myopia was associated with corneal flattening, increased total corneal astigmatism, anterior segment enlargement, and intraocular pressure elevation. The findings may inform the choice of intraocular lenses and the calculation of their power, help improve the surgical practice of refractive cataract procedures, and provide useful information on the centration and stability of intraocular lenses.

The Effect of Axial Length Elongation on Corneal Biomechanical Property

Background: To investigate the correlation between the corneal biomechanical parameter stress-strain index (SSI) and axial length (AL) in moderately elongated eye (MEE) and severely elongated eye (SEE).

Methods: This study included 117 eyes from 117 participants. Among them, 59 (50.4%) had MEE (AL<26 mm) and 58 (49.6%) had SEE (AL≥26 mm). AL was measured using Lenstar LS-900, and central corneal thickness (CCT) and anterior chamber volume (ACV) were measured using Pentacam. SSI was measured via corneal visualisation Scheimpflug technology (Corvis ST). Kolmogorov-Smirnov test, Student’s t-test, and Pearson and partial correlation analyses were used for statistical analyses.

Results: The mean (±SD) SSI was 1.08 ± 0.15 in the MEE group and 0.92 ± 0.13 in the SEE group (p < 0.01). SSI was positively correlated with age (MEE: r = 0.326, p < 0.05; SEE: r = 0.298, p < 0.05) in both groups; it was negatively correlated with AL (r = −0.476, p < 0.001) in the MEE group but not in the SEE group (p > 0.05). CCT was negatively correlated with AL (r = −0.289, p < 0.05) and ACV positively correlated with AL (r = 0.444, p < 0.001) in the MEE group. Neither CCT nor ACV was correlated with AL (p > 0.05) in the SEE group.

Conclusion: Corneal biomechanical parameter SSI, which represents the stiffness of corneal tissue, was lower in the SEE group than in the MEE group. When analyzed separately, SSI was negatively correlated with AL in the MEE group, but not in the SEE group, which may provide insight into different ocular growth patterns between lower myopia and higher myopia.

Understanding the role of corneal biomechanics-associated genetic variants by bioinformatic analyses

PURPOSE

To analyze functions of corneal biomechanical properties (CBP)-related variants as corneal resistance factor (CRF) and corneal hysteresis (CH).

METHODS

Related single nucleotide polymorphisms (SNPs) and genes were identified from NHGRI-EBI GWAS catalog, GWASdb v2 and possible data in published studies. HaploReg v4.1 was used to find linkage SNPs. Functional annotations were performed by GWAVA, CADD and RegulomeDB. GTEx Portal database was used to find out expression quantitative trait locus (eQTL) association. Enrichr was used to annotate the function of GWAS gene and the associated signal pathway. STING (v11.0) database was utilized for protein interaction and network construction.

RESULTS

The integration of 302 CH-associated and 420 CRF-associated lead SNPs has produced 531 CBP-associated lead SNPs. A total of 5,324 proxy variants identified using the HaploReg v4.1 and lead SNPs were functionally annotated. Based on the threshold (CADD ≥ 10, GWAVA ≥ 0.4 and RegulomeDB < rank 3), 23 prioritized putative regulatory SNPs were identified. Eight prioritized eQTL variants (rs75203695, rs34861673, rs846766, rs11024102, rs1377416, rs3829492, rs9934438 and rs197912) were found with strong potential of CBP regulation. It was indicated that CBP-associated genes were significantly enriched in extracellular matrix receptor interaction pathway, closely related to the phenotype of corneal dystrophy and keratoconus. COL1A1, SMAD3, BMP4 and RUNX2 occupied the core position in the co-expression network.

CONCLUSIONS

Data integrative analysis can evaluate CBP variations and explore collagen and extracellular matrix pathways in CBP regulation, which is a promising tool to investigate biological process of corneal diseases.

Biomechanical Glaucoma Factor and Corneal Hysteresis in Treated Primary Open-Angle Glaucoma and Their Associations With Visual Field Progression

Purpose

To investigate the relationship between biomechanical glaucoma factor (BGF) measured with Corvis ST and glaucomatous visual field (VF) progression, compared to corneal hysteresis (CH) measured with ocular response analyzer using a longitudinal dataset of primary open-angle glaucoma (POAG). The discriminative powers of BGF and CH were also compared using a cross-sectional dataset.

Methods

The longitudinal dataset included 166 POAG eyes. The rate of VF change during the follow-up period was evaluated using the mean of 52 pointwise total deviations in the Humphrey 24-2 field test. Variables associated with the VF progression rate were identified from BGF, CH, age, baseline VF severity, and intraocular pressure during the VF follow-up period by identifying the optimal model. The cross-sectional dataset included 68 POAG eyes and 68 healthy eyes. Using this dataset, the area under the curve (AUC) values of the receiver-operating curve were compared between CH and BGF.

Results

The optimal multivariate linear mixed model to describe the VF rate included age and CH, but not BGF. Between POAG and healthy eyes, CH was statistically different (P < 0.001), although this was not the case with BGF. The AUC values were 0.61 and 0.71 for BGF and CH, respectively (P = 0.027).

Conclusions

CH, but not BGF, was associated with VF progression in POAG patients under treatment. BGF was not useful to discriminate POAG between treated and normal eyes.

Association Between Severity of Myopia and Deformation Characteristics of the Cornea Based on Propensity Score Matching Analysis

PURPOSE

To investigate the relationship between severity of myopia and corneal deformation characteristics after removing confounding factors using propensity score matching (PSM) analysis.

METHODS

A prospective study was conducted from April 1 to December 30, 2019 in Tianjin Eye Hospital. Participants were divided into low (spherical equivalent [SE] > -6.00 diopters) and high (SE ⩽ -6.00 diopters) myopia groups. Corneal deformation parameters were obtained using corneal visualization Scheimpflug technology. PSM analysis was conducted to minimize the effect of confounding factors (age, intraocular pressure, and corneal thickness) on corneal deformation. Correlation analysis and logistic regression models were applied to investigate the relationships between SE and corneal deformation parameters.

RESULTS

A total of 2,126 eyes from 1,063 patients with a mean age of 23.81 ± 5.68 years were enrolled. The left and right eyes were analyzed separately. After PSM analysis, logistic regression indicated that the peak distance was a significant indicator for high myopia in both eye models (left: odds ratio [OR] = 1.978, 95% CI: 1.303 to 3.004; right: OR = 2.089, 95% CI: 1.362 to 3.202; P < .001). The maximum amplitudes of deformation and deflection and peak distance were significantly negatively correlated with SE in both eyes, whereas the whole eye movement was significantly positively correlated with SE (P < .01), as well as the deformation amplitude at the second applanation (P < .001).

CONCLUSIONS

Eyes with high myopia exhibited larger deformation and deflection amplitude compared to eyes with low myopia. The high distance between bending points of the cornea at the highest concavity (peak distance) may be a feature of high myopia. [J Refract Surg. 2021;37(5):344-350.].

The Sociodemographic and Risk Factors for Keratoconus: Nationwide Matched Case-Control Study in Taiwan, 1998-2015

PURPOSE

The aim of this study was to determine the sociodemographic and risk factors for keratoconus (KC) patients with a nationwide Asian database.

DESIGN

Population-based matched case-control study.

METHODS

We performed a secondary data analysis of the Taiwan National Health Insurance Research Database (NHIRD). Cases were patients with newly diagnosed KC in 1998-2015. Controls were patients without KC and matched 4:1 with the KC cases by age, sex, and index date. Comorbidities diagnosed before KC included diabetes mellitus (DM), asthma, allergic rhinitis, mitral valve prolapse, collagen vascular disease, aortic aneurysm, Down syndrome, sleep apnea, depression, hyperlipidemia, astigmatism, and myopia. Conditional logistic regression with forward selection were used to obtain risk factors for KC.

RESULTS

A total of 5,055 patients with KC were matched with 20,220 controls. The average age at KC first diagnosis was 29.76 years. Individuals who lived in suburban and rural area had lower odds ratio of KC (adjusted odds ratio [OR] 0.86, 95% confidence interval [CI] 0.80-0.94; and 0.73, 95% CI 0.67-0.79; respectively) when comparing with those who lived in urban area. Multivariate analysis revealed that Down syndrome, astigmatism, myopia, allergic rhinitis, and asthma were positively associated with KC with adjusted odds ratios (adjusted OR 8.69, 95% CI 3.74-20.19; 6.23, 95% CI 5.35-7.24; 2.99, 95% CI 2.70-3.32; 1.22, 95% CI 1.14-1.32; and 1.18, 95% CI 1.07-1.30, respectively). On the other hand, hyperlipidemia, depression, and DM (uncomplicated and complicated) were negatively associated with KC (adjusted OR 0.67, 95% CI 0.59-0.77; 0.58, 95% CI 0.48-0.71; 0.77, 95% CI 0.64-0.93; and 0.61, 95% CI 0.44-0.86, respectively).

CONCLUSIONS

Our study found that patients with hyperlipidemia, depression, or DM were less likely to have KC, and patients with asthma, allergic rhinitis, astigmatism, myopia, or Down syndrome had higher odds ratio of KC.

Corneal Biomechanical Properties in Varying Severities of Myopia

Purpose: To investigate corneal biomechanical response parameters in varying degrees of myopia and their correlation with corneal geometrical parameters and axial length.

Methods: In this prospective cross-sectional study, 172 eyes of 172 subjects, the severity degree of myopia was categorized into mild, moderate, severe, and extreme myopia. Cycloplegic refraction, corneal tomography using Pentacam HR, corneal biomechanical assessment using Corvis ST and Ocular Response Analyser (ORA), and ocular biometry using IOLMaster 700 were performed for all subjects. A general linear model was used to compare biomechanical parameters in various degrees of myopia, while central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered as covariates. Multiple linear regression was used to investigate the relationship between corneal biomechanical parameters with spherical equivalent (SE), axial length (AXL), bIOP, mean keratometry (Mean KR), and CCT.

Results: Corneal biomechanical parameters assessed by Corvis ST that showed significant differences among the groups were second applanation length (AL2, p = 0.035), highest concavity radius (HCR, p < 0.001), deformation amplitude (DA, p < 0.001), peak distance (PD, p = 0.022), integrated inverse radius (IR, p < 0.001) and DA ratio (DAR, p = 0.004), while there were no significant differences in the means of pressure-derived parameters of ORA between groups. Multiple regression analysis showed all parameters of Corvis ST have significant relationships with level of myopia (SE, AXL, Mean KR), except AL1 and AL2. Significant biomechanical parameters showed progressive reduction in corneal stiffness with increasing myopia (either with greater negative SE or greater AXL), independent of IOP and CCT. Also, corneal hysteresis (CH) or ability to dissipate energy from the ORA decreased with increasing level of myopia.

Conclusions: Dynamic corneal response assessed by Corvis ST shows evidence of biomechanical changes consistent with decreasing stiffness with increasing levels of myopia in multiple parameters. The strongest correlations were with highest concavity parameters where the sclera influence is maximal.