SBK & ASA biomechanically safer than LASIK

With regards to maintaining corneal biomechanics, sub-Bowman's keratomileusis (SBK) and advanced surface ablation (ASA) are improvements over conventional LASIK, according to a report published in the January issue of the Journal of Refractive Surgery.

Daniel Dawson and colleagues from Emory University and Emory Vision, Atlanta, Georgia, USA conducted histologic, ultrastructual and cohesive tensile strength evaluations on 25 normal human corneal specimens, 206 uncomplicated LASIK specimens, 17 uncomplicated SBK specimens, four uncomplicated PRK specimens, two uncomplicated ASA specimens, five keratoconus specimens, 12 postoperative LASIK ectasia specimens and one postoperative PRK ectasia specimen compared with previously published studies.

The researchers found that histological and ultrastructual studies of normal corneas revealed significant differences in the direction of collagen fibrils and/or the degree of lamellar interweaving in Bowman's layer, the anterior third of the corneal stroma, the posterior two-thirds of the corneal stroma and Descemet's membrane. Cohesive tensile strength testing supported these findings, as the stronger, more rigid regions of the cornea were located anteriorly and peripherally.

These results suggest that ASA, and secondarily SBK, should be biomechanically safer than conventional LASIK with regard the risk of causing keratectasia.