Assessment of corneal biomechanics in anisometropia using Scheimpflug technology

Corneal Biomechanical Characteristics and Correlation Analysis in Children With Different Refractive States

Purpose: To investigate the correlation between corneal biomechanical characteristics and refractive status in adolescents aged 5-13 years. Methods: A cross-sectional study involved 339 children aged 5-13 with a spherical equivalent (SE) range from -6.00 to +2.00 diopters. Axial length (AL) was measured by IOL Master, corneal biomechanical parameters by Corvis ST, and anterior segment parameters by Pentacam. According to SE of right eye, the subjects were divided into moderate myopia, mild myopia, and emmetropia group. The correlation between AL and SE and corneal biomechanical parameters was analyzed. The corneal biomechanical parameters of the three groups were also compared. Results: The A2V value in the moderate myopia group was significantly lower than that in both the mild group and emmetropia group (p < 0.001). PD in the moderate group was higher than that in the mild group (p < 0.05), while PD in mild myopia was higher than that in emmetropia (p < 0.05). The SSI in the emmetropia group was significantly higher than that in the other two groups (all p < 0.001), and the SSI in the mild group was higher than that in the moderate group (p < 0.01). The A2V value in the 11-13 years old group was lower than that in the 5-7 years old group (p < 0.001) and 8-10 years old group (p < 0.01). PD in the 11-13 years old group was significantly higher than that in the 8-10 years old group (p < 0.001), and PD in the 8-10 years old group was significantly higher than that in the 5-7 years old group (p < 0.01). The SSI in the 5-7 years old group was significantly higher than that in the 8-10 years old group (p < 0.001), and the SSI in the 8-10 years old group was significantly higher than that in the 11-13 years old group (p < 0.05). AL was positively correlated with PD and negatively correlated with SSI and A2V. SE was positively correlated with A2V and SSI and negatively correlated with PD. Conclusions: Corneal stiffness seems to decrease with the increase of SE. The changes of SSI, PD, and A2V were statistically significant and can be predictors of myopia progression in adolescents aged 5-13 years.

Long-term Corneal Biomechanical Properties of Thin Corneas After Small Incision Lenticule Extraction Surgery: A Prospective Controlled Study

PURPOSE

To investigate long-term corneal biomechanical changes in thin corneas after small incision lenticule extraction (SMILE).

METHODS

Patients with indications for SMILE were enrolled in this study between November 2017 and March 2018. Patients were matched for age, spherical diopter, cylinder, spherical equivalent (SE), and lenticule thickness (LT), and then categorized into the thin cornea group (preoperative thinnest central corneal thickness [CCT] of 500 µm or less, 32 eyes) or normal cornea group (CCT of greater than 500 µm, 32 eyes). Corneal biomechanical properties were measured using the Corvis ST system. Data were collected at 1 day, 3 weeks, 3 months, and 3 years postoperatively.

RESULTS

At 3 years postoperatively, the safety indexes were 1.06 ± 0.12 and 1.09 ± 0.12 (P = .23) in the thin cornea and normal groups, respectively; the respective effective indexes were 0.89 ± 0.23 and 0.98 ± 0.18 (P = .12). Recovery of overall corneal stiffness was observed in both groups. Comparative analysis of biomechanical parameters revealed that the change between preoperative and 3-year postoperative values was smaller in the thin cornea than in the normal group, without statistical significance. Correlation analysis showed that SE, LT, and CCT were the main parameters affecting changes in corneal biomechanical properties in the normal group. No significant correlations were found between the stress-strain index, Corvis biomechanical index for laser vision correction, and preoperative CCT or age.

CONCLUSIONS

With rigorous preoperative screening and appropriate surgical design, thin corneas are biomechanically stable in the long term after SMILE. Moreover, postoperative biomechanical strength increases over time. [J Refract Surg. 2025;41(1):e39-e49.].

Study on the impact of refractive anisometropia on strabismus, stereopsis, and amblyopia in children

To preliminarily explore the correlation between different types and degrees of refractive errors and strabismus, amblyopia, and stereopsis. A retrospective collection was conducted on a total of 145 patients with anisometropia who visited our hospital for strabismus and pediatric ophthalmology from January 2023 to August 2023.Based on the nature of anisometropia in both eyes, it was divided into 4 groups: Farsighted anisometropia (36 cases); myopic anisometropia (38 cases); astigmatic anisometropia (35 cases); mixed anisometropia (36 cases), and 30 children with normal vision were collected. Both groups of subjects underwent routine slit lamp and fundus examinations to exclude other organic eye diseases. The test indexes were: visual acuity, diopter, strabismus, far-stereoscopic vision, near-stereoscopic Titmus, and random static zero-order stereoscopic vision. The results of this study showed that compared with the normal control group, the incidence of strabismus was higher in the anisometropia group. When the refractive error was ≥1.00D, the far stereopsis and random dot static 0-order stereopsis in the anisometropia group decreased more significantly, and the difference between the groups was statistically significant (P < .05). Far-sighted and mixed astigmatism were more prone to amblyopia than myopia and regular astigmatism (P < .05). However, there was no statistical difference in near stereopsis Titmus between the anisometropia group and the control group (P > .05). Children with anisometropia are more likely to have strabismus, stereopsis and amblyopia than normal children.

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.

Characterization of Corneal Biomechanics Using CORVIS ST Device in Different Grades of Myopia in a Sample of Middle Eastern Ethnicity

Purpose

To characterize corneal biomechanical properties using the CORVIS-ST device in myopic individuals.

Methods

This prospective cross-sectional study included patients with myopia. Our study included 154 eyes of 154 myopic patients aged between 18 and 40 years, with stable refraction for at least 2 years. A full ophthalmological examination and corneal tomography were performed using a Pentacam HR device. Corneal biomechanical parameters were assessed using the CORVIS-ST device in mild, moderate, severe, and extreme myopia groups.

Results

Statistically significant differences were observed in the DA ratio (p = 0.033), SP-A (p=0.009), CBI (p=0.041), SSI (p=0.000), and Peak distance (p = 0.032). In correlation with different Corvis ST biomechanical variables, SE was found to be correlated with DA ratio(r=-0.191, p=0.018), SP-A(r=0.199, p=0.013) and SSI(r=-0.336, p=0.000), while in multiple regression analysis, SE was found to be independently correlated with SSI and peak distance(p=0.036,0.038 respectively) while the grade of myopia was found to be independently correlated with SP-A(p=0.034).

Conclusion

SSI, Peak distance, and SP-A were independently related to SE and myopia grade, confirming the hypothesis that eyes with higher myopia are more deformable and less stress resistant.

Evaluation of changes in corneal biomechanics after orthokeratology using Corvis ST

PURPOSE

To investigate the alterations in corneal biomechanical metrics induced by orthokeratology (ortho-k) using Corvis ST and to determine the factors influencing these changes.

METHOD

A prospective observational study was conducted to analyze various Corvis ST parameters in 32 children with low to moderate myopia who successfully underwent ortho-k lens fitting. Corneal biomechanical measurements via Corvis ST were acquired at six distinct time points: baseline (pre) and 2 h (pos2h), 6 h (pos6h), and 10 h (pos10h) following the removal of the first overnight wear ortho-k, one week (pos1w) and one month (pos1m) subsequent to the initiation of ortho-k.

RESULT

Significant differences were observed in Corvis ST Biomechanical parameters DAR2, IIR, CBI, and cCBI post ortho-k intervention. The integration of covariates (CCT, SimK, and bIOP) mitigated the differences in DAR2, IIR, and cCBI, but not in CBI. Initially, the stiffness parameter at first applanation, SP-A1, did not demonstrate significant variations, but after adjusting for covariates, noticeable differences over time were observed. The Stress-Strain Indeces, SSIv1 and SSIv2, did not manifest considerable changes over time, irrespective of the adjustment for covariates. No significant disparities were identified among different ortho-k lens brands.

CONCLUSION

Corneal biomechanics remained consistent throughout the one-month period of ortho-k lens wear. The observed changes in Corvis ST parameters subsequent ortho-k are primarily attributable to alterations in corneal pachymetry and morphology, rather than actual alterations in corneal biomechanics. The stability of corneal biomechanics post ortho-k treatment suggests the safety of this approach for adolescents from a corneal biomechanics perspective.

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.

Changes in Stress-Strain Index in School-Aged Children: A 3-Year Longitudinal Study

Purpose

To determine three-year change of the corneal biomechanical parameter stress-strain index (SSI) in schoolchildren aged 7- 9 years and their correlation with refractive error and axial length (AL).

Methods

This is a prospective cohort study. Data of the AL, refractive error, and corneal biomechanical parameter SSI were collected at baseline and a 3-year follow-up for 217 schoolchildren. SSI, AL, and refractive error were measured via corneal visualization Scheimpflug technology (Corvis ST), IOLMaster biometry, and cycloplegic refraction. Three years of changes in SSI and its association with refractive error and AL were analyzed. Participants were divided into persistent nonmyopia (PNM), newly developed myopia (NDM), and persistent myopia (PM). The three-year difference in SSI among the three groups was analyzed.

Results

After three years of follow-up, the corneal biomechanical parameter SSI decreased in all participants (P < 0.01). There was a negative correlation between the change in SSI and the change in AL (r = -0.205, P=0.002) and a positive correlation between the change in refractive error (r = 0.183, P=0.007). After three years of follow-up, there was a decrease in the SSI for the NDM, PM, and PNM participants, with a median change of -0.05 for PNM and -0.13 and -0.09 for the NDM and PM, respectively. There was a significant decrease in corneal biomechanical properties for NDM patients compared with PNM patients (P < 0.01).

Conclusion

In 7- to 9-year-old schoolchildren, SSI decreased after three years of the longitudinal study, and the change in SSI was correlated with the change in AL and refractive error. There was a rapid decrease in corneal biomechanical properties among newly developed myopic patients.