Changes in corneal biomechanics and posterior corneal surface elevation after FS-LASIK.

AIM: To investigate the changes in corneal biomechanics and posterior corneal surface elevation after femtosecond laser-assisted in situ keratomileusis (FS-LASIK). METHODS: Totally 197 eyes of 100 patients who underwent the FS-LASIK from April 2022 to November 2022 were included. They were divided into three groups according to the ratio of residual corneal stroma thickness/corneal thickness (RCST/CT): Group I (50%≤RCST/CT<55%, 63 eyes of 32 patients), Group II (55%≤RCST/CT<60%, 67 eyes of 34 patients), and Group III (RCST/CT≥60%, 67 eyes of 34 patients). The intraocular pressure (IOP), corneal compensated IOP (IOPcc), corneal hysteresis (CH) and corneal resistance factor (CRF) were measured immediately, 1, and 3mo postoperatively by ocular response analyzer (ORA) and the posterior elevation difference (PED) was measured by Pentacam. RESULTS: After operation, IOP, CH, CRF, and PED were statistically different among the three groups (F=12.99, 31.148, 23.998, all P<0.0001). There was no statistically significant difference in IOPcc among the three groups (F=0.603, P>0.05). The IOP, IOPcc, CH, and CRF were statistical changed after surgery (F=699.635, 104.125, 308.474, 640.145, all P<0.0001). The PED of Group I was significantly higher than that of Group II (P<0.05), and Group II was significantly higher than that of Group III (P<0.05). The PED value of 3mo after surgery decreased in each group compared with 1mo after surgery, but there was no statistical difference (Group I: t=0.82, P=0.41; Group II: t=0.17, P=0.87; Group III: t=1.35, P=0.18). The correlation analysis of corneal biomechanical parameter changes with PED at 1mo and 3mo after surgery showed that ΔIOP, ΔIOPcc, ΔCH, and ΔCRF were not correlated with PED value in three groups (P>0.05). CONCLUSION: The smaller the RCST/CT, the greater effect on corneal biomechanics and posterior surface elevation. There is no correlation between changes in corneal biomechanics and posterior corneal surface elevation in the range of RCST/CT≥50%.

Factors Associated with the Posterior Corneal Surface Elevation in Mmyopic Eye

PURPOSE: To know the factors associated with the posterior corneal surface elevation in myopic eye. METHODS: The posterior corneal surface elevation (PCSE), keratometry, central corneal thickness (CCT), peripheral corneal thickness (PCT), thinnest corneal thickness (TCT) were measured in 64 right myopic eyes with the Orbscan topography system. The correlation between PCSE and age, refractive error, intraocular pressure (IOP), keratometry, CCT, TCT, PCT, PCT-CCT, PCT/CCT, PCT-TCT, and PCT/TCT was evaluated. RESULTS: The posterior corneal surface elevation has correlation with CCT (r:.0.3306, p:0.0071), TCT ( r :.0.4094, p:0.0007), PCT-CCT(r:0.3326, p:0.0068), PCT/CCT (r:0.3759, p:0.0020), PCT-TCT (r: 0.4750, p:0.0001), and PCT/TCT (r:0.5145, p:0.0001) but does not have correlation with age, keratometry, refractive error, IOP (r:.0.0627, p:0.6225), and PCT. CONCLUSIONS: In myopic eyes, the posterior corneal surface elevation correlates with central corneal thickness and specifically the ratio PCT to TCT.