Correlation Analysis of Bowman’s Layer Microdistortions and Corneal Biomechanics Changes Evaluated by Brillouin Microscopy After KLEx

Purpose: To investigate the correlation between Bowman’s layer microdistortions and the changes in corneal biomechanics evaluated by Brillouin microscopy after Keratorefractive Lenticule Extraction (KLEx). Methods: This study included forty-three right eyes that underwent KLEx, with a mean spherical equivalent of − 5.89 ± 1.44 diopters. Metric M, the total width of the microdistortions, was calculated to indicate the quantity of Bowman’s layer microdistortions according to the images measured using Fourier-domain optical coherence tomography (FD-OCT) 1month postoperatively. Corneal biomechanical metrics were obtained and analyzed using Brillouin microscopy preoperatively and 1 month postoperatively. Results: Bowman’s layer microdistortions were observed using FD-OCT one month postoperatively, revealing a total width of 502 (175, 698) μm of the four meridians. Central, mean, minimum (Min), maximum (Max), and spatial standard deviation (SSD) Brillouin modulus (BM) quantified by Brillouin microscopy were 2.888 ± 0.074 GPa, 2.878 ± 0.041 GPa, 2.783 ± 0.059 GPa, 2.956 ± 0.053 GPa, 0.217 ± 0.063 GPa before KLEx, respectively; these changed to 2.800 ± 0.058 GPa (P < 0.001), 2.821 ± 0.033 GPa (P < 0.001), 2.734 ± 0.040 GPa (P < 0.001), 2.908 ± 0.051 GPa (P < 0.001), 0.223 ± 0.062 GPa (P =0.666) 1 month after KLEx, respectively. Metric M was correlated with value’s changes of Mean BM (r =0.57, P < 0.001&ast;) and Min BM (r =0.35, P =0.02), controlling for spherical equivalent. Conclusion: In this study, the alterations in corneal biomechanics following KLEx are positively correlated with the range of Bowman’s layer microdistortions. Increased Bowman’s layer microdistortions may lead to a more pronounced decline in the corneal biomechanics. These findings may be useful for evaluating KLEx outcomes, detecting complications early, and optimizing patient monitoring. Plain Language Summary: After a type of corneal laser surgery: Keratorefractive Lenticule Extraction (KLEx), tiny irregularities were observed in a specific layer of the cornea (Bowman’s layer). The researchers used a special imaging technique to measure corneal stiffness before and after the procedure. This study aimed to determine the relationship between small irregularities and the cornea’s stiffness. The measurements showed that corneal stiffness decreased one month after surgery. This study found that the extent of tiny irregularities in the Bowman’s layer was linked to the amount of change in corneal stiffness. Specifically, a larger area of these irregularities was associated with a larger change in stiffness measurements. In conclusion, changes in corneal strength after KLEx surgery are related to the presence and extent of these small structural irregularities. The flowchart illustrates a study on corneal biomechanics in adults undergoing Keratorefractive Lenticule Extraction. Participants: The right eye of adults with a mean spherical equivalent of -5.89 ± 1.44 diopters (n=43). Before surgery: Obtaining corneal biomechanical metrics by Brillouin microscopy. 1 month postoperatively: Obtaining corneal biomechanical metrics by Brillouin microscopy. Calculating the total width of Bowman’s layer microdistortions in four meridians measured by FD-OCT. Results: Total width of Bowman’s layer microdistortions is positively correlated with alterations in corneal biomechanics.A flowchart of corneal biomechanics study before and after surgery. Keywords: bowman’s layer microdistortions, brillouin microscopy, brillouin modulus, corneal biomechanics