Abstract
Significance: Our study found that SP-A1 (stiffness parameter at time of first applanation) was statistically different between post-laser-assisted subepithelial keratomileusis (LASEK) and post-small incision lenticule extraction (SMILE) eyes. The stiffness of keratoconus was lower than that of post-refractive surgery corneas.Purpose: To compare corneal biomechanics among post-SMILE, post-LASEK, and keratoconic eyes.Methods: In this retrospective study, 36 eyes of 36 patients after SMILE, 36 eyes of 36 patients after LASEK, and 36 eyes of 36 patients with keratoconus with matching (±5 μm) central corneal thickness (CCT) were examined using Scheimpflug corneal topography (Pentacam HR) and dynamic Scheimpflug analyzer (CorVis ST). Mixed linear model analysis with Bonferroni-adjusted post-hoc comparisons was performed to compare the differences in corneal biomechanics and topographic parameters among the three groups with the CCT and the bIOP (intraocular pressure with biomechanical correction) as the random factor.Results: All groups had comparable CCT at baseline. The bIOPs between the three groups were comparable. The mean values of the Belin/Ambrósio Deviation (BAD-D) in the keratoconus group were significantly higher than those of the SMILE (post hoc p < 0.001) and LASEK groups (post hoc p < 0.001). The SP-A1 in the keratoconus group was the lowest when compared with those of the SMILE (post hoc p = 0.003) and LASEK groups (post hoc p < 0.001). The SMILE group SP-A1 values were slightly lower than those of the LASEK group (post hoc p = 0.044).Conclusions: Keratoconus eyes were significantly softer when compared to post-refractive surgery corneas with comparable corneal thickness in terms of SP-A1 and BAD-D values, while the LASEK group may have the greatest stiffness. Post-SMILE and post-LASEK corneas showed significant differences in SP-A1.
Highlights
Keratoconus is a bilateral, progressive ectatic disorder, which causes thinning of the corneal stroma, irregular astigmatism, and loss of best spectacle-corrected vision [1,2,3]
The present study investigated the differences in corneal topography and biomechanics in keratoconus and post-refractive surgery eyes using CorVis ST and Pentacam HR platforms
We noted that SP-A1 was the lowest in the keratoconus group, while it was highest in the laser-assisted subepithelial keratomileusis (LASEK) group
Summary
Keratoconus is a bilateral, progressive ectatic disorder, which causes thinning of the corneal stroma, irregular astigmatism, and loss of best spectacle-corrected vision [1,2,3]. The prevalence is around 1/2,000 in the general population [2]. Another form of corneal ectasia is seen after refractive surgeries, mainly after laser in situ keratomileusis (LASIK) [4,5,6]. Small incision lenticule extraction (SMILE) [7, 8] and laser-assisted subepithelial keratomileusis (LASEK) are stromal flap-free surgeries, which are rarely associated with corneal ectasia. This might be attributed to the lack of corneal flap and other factors such as corneal stromal bed thickness [9]. PostSMILE and post-LASEK eyes are good models for understanding the effect of tissue removal on the cornea
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