Comparison of Forward Shift of Posterior Corneal Surface after Operation between LASIK and LASEK

Abstract

Purpose: To compare the forward shift of the posterior corneal surface as a function of time after surgery between successful laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK). Methods: Twenty-two eyes from 14 patients who underwent LASIK and 19 eyes from 10 patients who underwent LASEK were reviewed retrospectively. The uncorrected visual acuity, spherical equivalent and pachymetry were obtained before and 1 or 2 weeks and 2, 6, 12, and 24 months after surgery. The change in the elevation of the posterior corneal surface was assessed using the difference map of an Orbscan II (Bausch and Lomb, Salt Lake City, Utah, USA), which was generated from the preoperative and subsequent postoperative elevation map. Results: One or 2 weeks after LASIK and LASEK, the posterior corneal surface had shifted forward by 18.00 and 25.90 µm, respectively (p = 0.008). However, the mean posterior corneal surface reduced by 3.05 µm from 1 or 2 weeks to 2 years in the LASIK group (p = 0.359). In contrast, the mean posterior corneal surface had reduced by 12.40 µm in the LASEK group (p = 0.004). This forward shift did not return to the corneal normal elevation observed prior to surgery in the two groups. Conclusions: Refractive surgery induced a forward shift of the posterior corneal surface early postoperatively in the LASIK and LASEK groups, and this change after LASEK was significantly larger than that observed after LASIK. The posterior corneal surface gradually shifted backwards depending on the time course in both groups, but they did not return to the preoperative levels.

Corneal imaging with slit‐scanning and Scheimpflug imaging techniques

“…Where the Orbscan was applied to evaluate differences between pre-operative and postoperative posterior corneal elevation values, several cases of posterior corneal ectasia were detected. [15][16][17][18][19] On the other hand, the Pentacam revealed no significant changes in posterior elevation values, as is generally expected in keratorefractive surgery. 20,21 Additionally, the Orbscan II also exhibited low repeatability in the measurement of post-operative posterior corneal surface elevation.…”

“…These findings are aligned with the results of some previous research work on the influence of keratorefractive surgery on the posterior corneal surface. Where the Orbscan was applied to evaluate differences between pre‐operative and post‐operative posterior corneal elevation values, several cases of posterior corneal ectasia were detected 15–19 . On the other hand, the Pentacam revealed no significant changes in posterior elevation values, as is generally expected in keratorefractive surgery 20,21 .…”

Posterior corneal surface differences between non‐laser in situ keratomileusis (LASIK) and 10‐year post‐LASIK myopic eyes

“…Many previous studies have reported forward shift of posterior surface after keratorefractive surgery based on the Orbscan system (Kim et al. ; Lee et al. ; Martin & Rachidi ).…”

“…Previous studies, using scanning slit‐beam corneal topography (Orbscan corneal topography), mostly reported a forward shift of the posterior corneal surface (Kim et al. ; Lee et al. ).…”

“…Furthermore, the risk of subclinical corneal ectasia after myopic LASIK has been a controversial issue over the last decade. Previous studies, using scanning slitbeam corneal topography (Orbscan corneal topography), mostly reported a forward shift of the posterior corneal surface (Kim et al 2006;Lee et al 2007). However, the failure of the Orbscan to accurately locate the posterior corneal surface after LASIK has been well documented.…”