Corneal thickening and central flattening induced by femtosecond laser hyperopic-shaped intrastromal lenticule implantation

Abstract

Purpose: To investigate the feasibility of the procedure and the modifications of the corneal curvature and profile obtained with a novel technique of stromal-lentoid implantation in ex vivo human corneas.

Design: Experimental ex vivo study in human corneas.

Materials and methods: Twelve stromal lentoids were produced by means of hyperopic femtosecond lenticule extraction (FLEx) with the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) with a refractive power of +8.00 D and optical zone of 6.0 (six lenticules) and 5.0 mm (six lenticules), respectively. The posterior surface of these stromal lentoids presented a higher curvature with respect to the anterior surface and, therefore, the thinnest point is located at the center of the lenticule, gradually thickening towards the periphery. Another 12 corneas underwent femtosecond laser intrastromal pocket creation at a depth of 115 microns, for lenticule insertion. After intrastromal lenticule implantation the changes of corneal profiles were evaluated by means of corneal topography and anterior segment optical coherence tomography (OCT).

Results: The implantations of intrastromal lenticules were successful in all cases with proper distention and centration. A mid-peripheral forward shift of the anterior corneal surface along with a thickening (greater in periphery) was induced. There was a significant flattening of anterior corneal central areas of 7.31 ± 1.52 D (p = 0.002). Diameters of the flattening area were found to be consistently correlated with the optical zone diameter of the implanted lenticules (p = 0.006). Central flattening was similar in both groups. OCT pachymetry maps showed an increase of corneal thickness consistently correlated with implanted lentoid thickness and diameter.

Conclusion: The implantation of modified hyperopic-shaped intra-corneal stromal lentoid is a feasible and reproducible technique for achieving central corneal flattening while increasing thickness. Whether this procedure may be beneficial in the treatment of refractive errors or ectatic corneal disorders such as keratoconus merits further study.

Keywords: Femtosecond laser; Hyperopic femtosecond lenticule; Keratoconus; Lenticule implantation.