Small Incision Lenticule Extraction (SMILE) for Hyperopia: Optical Zone Centration

PURPOSE: To evaluate optical zone centration of hyperopic small incision lenticule extraction (SMILE). METHODS: This prospective study of 60 consecutive hyperopic SMILE procedures used the VisuMax femto second laser and matched LASIK procedures with the VisuMax and MEL 80 excimer lasers (Carl Zeiss Meditec AG, Jena, Germany). Inclusion criteria were maximum attempted hyperopic meridian of between +1.00 and +7.00 diopters (D) and astigmatism up to 6.00 D. For SMILE, the optical zone was between 6.3 and 6.7 mm, with a 2-mm transition zone. Two LASIK control groups (6.5- and 7-mm optical zone) were generated matched for spherical equivalent treated. In SMILE, the corneal vertex of the coaxially fixating eye was aligned with the vertex of the curved contact glass. In LASIK, the treatment was centered on the coaxially sighted corneal light reflex (first Purkinje image) with the contralateral eye (Seiler method). A tangential (instantaneous) curvature preoperative to 3 months postoperative difference map was generated for each eye. A fixed grid and set of concentric circles were superimposed on the difference map to measure the offset between the optical zone center and corneal vertex (0,0), and vector analysis was used for comparative analysis. RESULTS: Mean attempted spherical equivalent was + 5.61 +/- 0.96 D (range: + 3.20 to + 6.50 D) and mean cylinder was -0.96 +/- 0.62 D (range: 0.00 to -2.75 D) in the SMILE group. Mean age was 29 +/- 7 years (range: 19 to 52 years) in the SMILE group. Mean centration offset was 0.23 +/- 0.15 mm (range: 0 to 0.61 mm) for the SMILE group, 0.33 +/- 0.14 mm (range: 0.14 to 0.85 mm) for the 6.5-mm LASIK group, and 0.31 +/- 0.19 mm (range: 0.05 to 0.85 mm) for the 7-mm LASIK group. The mean centration offset for SMILE was less than that of both LASIK groups (P <.05). CONCLUSIONS: Optical zone centration of hyperopic SMILE was found to be similar to eye-tracker-centered hyperopic LASIK with the MEL 80 laser.