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Comparative Study
. 2025 Feb 27;24(1):26.
doi: 10.1186/s12938-025-01343-2.

A novel corneal indentation device for comparison of corneal tangent modulus before and after FS-LASIK in vivo

Yan Zhang #  1 , Junyu Lin #  1   2 , Shu-Hao Lu  3 , Jones Iok-Tong Chong  3 , Cheng Yang  1 , Jianqing Lan  1 , Wenjuan Xie  1 , Juan Li  1 , David Chuen-Chun Lam  3 , Dan Cao #  4 , Jin Zeng #  5
Affiliations
Comparative Study

A novel corneal indentation device for comparison of corneal tangent modulus before and after FS-LASIK in vivo

Yan Zhang et al. Biomed Eng Online. .

Abstract

Background: Corneal refractive laser surgery is widely used to correct myopia and astigmatism due to its safety and effectiveness. However, postoperative changes in corneal biomechanics, such as corneal ectasia, can occur, necessitating a deeper understanding of these changes. Finite Element Analysis has shown promise in predicting surgical outcomes based on corneal biomechanics. Devices like the Ocular Response Analyser (ORA) and Corvis ST provide noninvasive ways to measure corneal biomechanics, aiding in the assessment of corneal behavior post-surgery. Young's modulus and tangent modulus are crucial parameters for describing corneal elasticity, but there is limited data on the changes in tangent modulus following Femtosecond Laser-Assisted LASIK (FS-LASIK) in humans. This study aimed to investigate the effect of FS-LASIK on the corneal tangent modulus using a novel corneal indentation device (CID). The study sought to explore changes in corneal tangent modulus after FS-LASIK, taking into account central corneal thickness (CCT) and corneal radius, to enhance our understanding of the biomechanical changes induced by this surgical procedure.

Results: Sixty-six patients (66 eyes) underwent FS-LASIK, resulting in significant changes in CCT, corneal radius, and Goldmann intraocular pressure (GAT IOP) 6 months post-surgery (△CCT = - 88 ± 31 µm, △corneal radius = 0.81 ± 0.30 mm, △GAT IOP = - 3.2 ± 2.4 mmHg, p < 0.001) 6 months after surgery. However, corneal stiffness did not significantly change (△ = - 0.002 ± 0.011, p < 0.2). The corneal tangent modulus showed a significant increase post-surgery (△ = 0.263 ± 0.146, p < 0.001), exhibiting a negative correlation with CCT (r = - 0.68, P < 0.001) and a positive correlation with corneal radius (r = 0.71, P < 0.001). For each 1 mm increase in corneal radius, there was a 0.23 MPa increase in corneal modulus, and for every 100 µm reduction in corneal thickness, there was a 0.14 MPa increase in corneal modulus.

Conclusions: The corneal tangent modulus, influenced by corneal radius and CCT, increased significantly following FS-LASIK. This study highlights the biomechanical changes induced by FS-LASIK, with implications for understanding corneal behavior post-surgery and its potential impact on patient outcomes.

Keywords: Clinical trial; Corneal biomechanics; Corneal stiffness; Corneal tangent modulus; Femtosecond Laser-Assisted LASIK.

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Conflict of interest statement

Declarations. Ethical approval and consent to participate: The research protocols were approved by the Institutional Review Board at Guangdong Provincial People’s Hospital (No. GDREC2017206H(R2)). The study followed the tenets of the Declaration of Helsinki, and all subjects were thoroughly informed of the procedure and provided written informed consent. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Association Between GAT-IOP Reduction, Corneal Ablation Thickness, and Changes in Corneal Curvature
Fig. 2
Fig. 2
Distribution and Correlation of CCT, Mean R, and Corneal Modulus. The distribution and correlation between CCT, mean R, and corneal modulus indicated a stronger positive correlation between mean R and corneal modulus and a stronger negative correlation between CCT and corneal modulus
Fig. 3
Fig. 3
Corneal Tangential Tensile Stress after FS-LASIK
Fig. 4
Fig. 4
Corneal Indentation Device Setup
See this image and copyright information in PMC

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