BOWMAN'S LAYER BIOMECHANICAL IMPACT ASSESSED WITH EXTENSOMETRY AND QUASI-STATIC OPTICAL COHERENCE ELASTOGRAPHY

Published 2022 - 26th ESCRS Winter Meeting

Reference: MP07 | Type: Abstracts | DOI: 10.82333/1sve-dg70

Authors: Emilio A. Torres-Netto* ¹ , Sabine Kling ² , Bogdan Spiru ³ , Nikki Hafezi ⁴ , Hormoz Abdshahzadeh ⁵ , Walter Sekundo ³ , Farhad Hafezi ⁶

¹CABMM,University of Zurich,Zurich,Switzerland;Ophthalmology,ELZA Institute,Zurich,Switzerland;Faculty of Medicine,University of Geneva,Geneva,Switzerland, ²Computer Vision Laboratory,Swiss Federal Institute of Technology,Zurich,Switzerland, ³Ophthalmology,Phillips University of Marburg,Marburg,Germany, ⁴ELZA,ELZA Institute,Zurich,Switzerland, ⁵CABMM,University of Zurich,Zurich,Switzerland, ⁶Faculty of Medicine,University of Geneva,Geneva,Switzerland;Ophthalmology,ELZA Institute,Zurich,Switzerland

Purpose

Whether Bowman’s layer (BL) contributes to corneal biomechanical strength is subject to controversy. While atomic force microscopy has shown BL to have an E-modulus 3 times greater than corneal stroma, whole-cornea studies have failed to show that the BL plays a clinically significant role. We evaluated and compared Bowman's biomechanical impact on human corneas with two different technologies: stress-strain extensometry and quasi-static optical coherence elastography.

Setting

Laboratory for Ocular Cell Biology, Center for Applied Biotechnology and Molecular Medicine, University of Zurich, Zurich, Switzerland; ELZA Institute, Dietikon/Zurich, Switzerland; and Computer Vision Laboratory, Swiss Federal Institute of Technology, Zurich, Switzerland.

Methods

Fifty healthy human donor corneas were stripped of Descemet’s membrane and the endothelium as per DMEK. Corneas were divided groups in which BL was ablated with an excimer laser, or groups in which BL was left intact. Seperately, the elastic and viscoelastic material properties of 26 thin corneal flaps were then analyzed by two-dimension stress-strain extensometry. Additionally, corneal biomechanical behavior of 23 whole corneas were investigated with quasi-static optical coherence elastography (OCE) in order to quantify full corneal strain distributions.

Results

When evaluating the thin corneal lamellae, no significant differences between flaps with and without BL were observed in the tangential E-modulus, neither during preconditioning (p=0.086), nor in destructive testing until break (p=0.080). However, anterior stiffness in whole corneas with Bowman’s layer was significantly (p=0.043) higher than in corneas without. Interestingly, the differences in strain distribution observed between whole corneas with and corneas without BL were located inside the stroma, and not (as expected) on top of the anterior surface.

Conclusion

Corneal strain distribution is more complex than previously assumed. Although minor localized differences in corneal strain distribution of whole corneas were observed, the presence or absence of Bowman's layer did not alter corneal stiffness in corneal thin flaps. These results may have implications for both refractive laser surgery procedures, but also for Bowman's layer transplantation for keratoconus.