Biomechanical properties of the corneal stroma extracted during the SMILE surgery in myopia with varying axial length

One of the applied areas of biomechanics in ophthalmology involves studying changes in the fibrous coat of the eye in myopia. A series of studies using various methods has revealed alterations in the biomechanical properties of the sclera associated with progressive myopia due to structural and metabolic altering. However, corneal changes associated with myopia, and specifically those potentially influenced by the increase in axial length, remain less studied. Purpose. To study the biomechanical properties of the corneal stroma removed during small-incision lenticule extraction (SMILE) in myopia with varying axial length (AL). Material and methods. The study included 122 lenticules (stromal corneal fragments) obtained from patients aged 17—47 years during SMILE refractive correction for myopia. The preoperative spherical equivalent ranged from –0.75 to –13.25 D, and the AL varied between 22.64 and 29.05 mm. Baseline central corneal thickness (CCT) was 493.00—622.00 μm (mean 560.64±25.62 μm). Measurements were performed using a Bruker Bioscope Resolve atomic force microscope (Bruker, USA). Results. Selective assessment of the Young’s modulus (Y) for the anterior and posterior lenticule surfaces revealed comparable values (medians 51.00 and 53.60 kPa; minimum—maximum range 5.20—222.00 and 7.30—214.30 kPa, respectively). Analysis of the relationship between Y values and axial length showed a statistically significant but weak positive correlation for the anterior surface, in contrast to the posterior surface. A statistically significant inverse correlation was observed between Y and CCT: weak for the anterior surface and moderate for the posterior surface. Conclusion. Corneal fragments obtained during SMILE myopia correction provide a valuable model for biomechanical testing of the corneal stroma under conditions closely resembling in vivo physiology. The Young’s modulus values for the anterior and posterior lenticule surfaces were comparable and significantly correlated. The weak correlation between lenticule stiffness and axial length indirectly suggests minimal corneal biomechanical alterations associated with fibrous coat enlargement. The potential relationship between CCT and stromal biomechanics requires further investigation.