Short term changes in corneal stress-strain index and other corneal biomechanical parameters post-laser in situ keratomileusis

Abstract

Purpose: To report the short-term changes in a corneal stress-strain index (SSI) and other corneal biomechanical parameters post-laser in situ keratomileusis (LASIK) surgery. Methods: A retrospective study was conducted at a tertiary eye care center wherein patients who had undergone LASIK (microkeratome blade and femtosecond bladeless LASIK) between July and December 2019 were enrolled. Patients of age group 20–40 years, best-corrected visual acuity of 20/20, intraocular pressure (IOP) <22 mmHg, pre-LASIK pachymetry >500 microns, and corneal astigmatism ≤3.00 D were included. Subjects with a prior history of refractive surgery, any other ocular or systemic disease, poor-quality scans, intraoperative complications, and missing data were excluded. Corneal biomechanical properties including SSI were analyzed using Corvis ST and compared using the Paired T-test for each group separately at pre-LASIK, and 1-month post-operatively. Results: Overall, 202 eyes were reviewed, and 79 eyes fulfilled the inclusion criteria. Forty-three and 36 eyes had undergone Microkeratome Blade LASIK (Group I) and Femto LASIK (Group II), respectively. Overall, 29 and 26 corneal biomechanical parameters out of 33 changed significantly post-Microkeratome Blade LASIK and Femto LASIK, respectively. Statistically significant changes were noted in all the parameters at A1, maximum and Vinciguerra screening parameters ( P < 0.001), however, no changes were noted in SSI in both the groups when compared with the pre-surgery data. Conclusion: Though the reduction in SSI was not statistically significant, other biomechanical parameters showed significant biomechanical changes pre- and post-LASIK surgeries in both the groups. However, a long-term study with a larger sample size would be required to understand the changes and stability in SSI post-refractive surgery.

Change in the corneal material mechanical property for small incision lenticule extraction surgery

“…Other biomechanical parameters, including HC Deformation Amp., DA ratio, ARTh, IR, SP-A1, and CBI, all underwent significant changes after SMILE ( p < 0.001). This is consistent with the study by ( Kenia et al, 2021 ) that compared the SSI 1 month after laser in situ keratomileuses (LASIK) and femtosecond LASIK and found that its reduction was not statistically significant in either group.…”

Corneal stress-strain index in myopic Indian population

“…Ocular surgeries also have an impact on corneal biomechanics. [ 21 22 23 24 25 26 ] Corneal biomechanical parameters in refractive errors such as myopia have been assessed previously;[ 5 6 7 27 28 29 30 31 32 ] however, these reports lack information about corneal SSI. In the present study, we have assessed the corneal biomechanical parameters in myopic eyes, including extreme myopic errors.…”

Commentary: Corneal biomechanical assessment following refractive surgery: Past, present, and future

“…[ 6 ] There is only one study now showing SSI changes in early postoperative time following LASIK. [ 7 ] There are more studies needed using the novel SSI and CBI-LVC with longer-term follow ups and also involve the effects of long-term wound healing to check how LASIK differs from SMILE. Differentiating normal corneas postrefractive surgery from post refractive surgery ectasia Though several univariate indices provided by CORVIS ST have been variably successful in differentiating normal corneas from postrefractive surgery ectatic ones in the past, the best index as on date is the CBI-LVC, with sensitivity and specificity over 90% for a cutoff of 0.20.…”

“…[ 6 ] There is only one study now showing SSI changes in early postoperative time following LASIK. [ 7 ] There are more studies needed using the novel SSI and CBI-LVC with longer-term follow ups and also involve the effects of long-term wound healing to check how LASIK differs from SMILE.…”