Abstract
Purpose :
Several studies have shown that the anterior portion of the cornea is important for corneal stiffness. In the 1990s, experiments to determine the biomechanical properties of Bowman's layer failed to demonstrate that it significantly contributes to corneal biomechanics. However, recent surgical techniques such as small incision lenticule extraction and Bowman's layer transplantation suggest a role in corneal biomechanics. Here, we tested the biomechanical properties of Bowman's layer in healthy ex vivo human corneas using stress-strain extensometry.
Methods :
Twenty-six healthy human corneas were obtained following endothelial stripping for DMEK (Descemet membrane endothelial keratoplasty). The stripped corneas were preserved in tissue culture medium for a maximum of 7 days. Following manual removal of the epithelium, corneas were divided into two groups. In group 1, Bowman's layer was ablated with an excimer laser (20μm thick, 10mm OZ). In group 2, Bowman's layer was left intact. Then in both groups, a 110μm-thick lamella was cut from the anterior cornea with an automated microkeratome. Elastic and viscoelastic material properties were analyzed by 2D stress-strain extensometry between 0.03 and 0.7 N.
Results :
No significant differences between flaps with and without Bowman's layer were observed in the tangential elastic modulus, neither during preconditioning (874 70 vs 937 106 kPa, p=0.086), nor in destructive testing until break (1.03 0.14 vs 1.17 0.14 MPa, p=0.080). Similarly, no significant differences (p=0.08) were found in the stress after relaxation for 120s between flaps with (578 19 kPa) and without (558 35 kPa) Bowman's layer.
Conclusions :
The presence or absence of Bowman's layer did not alter the stiffness of a 110μm corneal lamella. Unlike in previous experiments, where whole corneas were analyzed, our measurements were performed in thin corneal flaps so that the relative biomechanical contribution of Bowman's layer was greater. Still, our analysis showed no difference in corneal stiffness between groups. These results may have implications not only for refractive laser surgery procedures, but also for the new technique of Bowman's layer transplantation in keratoconus.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.