EX-VIVO LENTICULE CUSTOMIZATION FOR STROMAL LENTICULE ADDITION KERATOPLASTY (SLAK)

To explore the optimal shape of customized lenticules for stromal lenticule addition keratoplasty (SLAK) for off-centered ectasia.

Departmentt of Medicine and Aging Sciences, University "G. D'Annunzio" Chieti, Italy.

Two different methods to create ex-vivo models of eccentric keratoconus were investigated. Twelve human corneas were used to create Model-1 by a hyperopic photorefractive keratectomy (PRK), and Model-2 by masked phototherapeutic keratectomy (PTK) on the anterior corneal surface, while both types received myopic ablation of the posterior surface. Keratoconus models underwent a modified femtosecond laser (FSL) flap-cut to create stromal pockets. Sixteen-human corneas underwent FSL dissection to obtain four lenticule types: Type-I (planar) and Type-II (negative) lenticules were used without modifications, while Type-III (customized-planar), and Type-IV (customized-negative) lenticules underwent further masked-PRK to obtain an asymmetric bow-tie shape. Topographic, aberrometric analysis, and AS-OCT were performed in all recipient corneas before, and after lenticule implantation.

The Keratoconus model was successfully reproduced. Tomographic analysis showed a significant inferiorly decentered corneal steepening with coherent stromal thinning. Model 2 reproduced better the curvature of real keratoconus. Lenticules Type-I implantation induced homogeneous corneal thickening and Type-III produced higher thickening in the inferior half of the cornea. Type II determined a maximal peripheral pachymetric increase, with a gradual reduction toward the center, and Type IV presented an asymmetric peripheral thickening. The topographic assessment showed a cone apex flattening in all cases, but it was significantly higher in Types II and IV. Customized lenticules improved significantly corneal surface regularity regarding Types I and II.

The approach of customizing lenticules by increasing their asymmetry and tailoring the re-shaping effects may improve SLAK outcomes in eccentric keratoconus.