Influence of FLEx and SMILE on corneal nerve density and ocular surface
Reviewed by Mrinal Rana

This was a prospective study designed to compare the influence of femtosecond lenticule extraction (FLEx) and small incision lenticule extraction (SMILE) on the corneal nerve density and ocular surface for myopic correction. Thirty patients underwent bilateral lenticule extraction. One eye was randomly picked for FLEx and the other had SMILE. Inclusion criteria included unsatisfactory visual acuity even with spectacle or contact lens correction, myopic refractive error ranging between -1 to -9D, corneal thickness >400mic and residual stromal bed of 250microns. Surgical procedure for FLEx and SMILE involved use of VisuMax femtosecond laser system with 500KHz repetition rate. The incision pattern followed an automated sequence of posterior surface of lenticule, then anterior surface of lenticule and side cut flap. After completion of laser sequence for FLEx the flap was lifted, lenticule grasped and extracted. The flap was repositioned and interface flushed and for SMILE, the spatula was inserted through the side cut over and under the lenticule to free it from its adhesions and then grasped and pulled out. Sub-basal nerve density was measured using confocal microscope (HRT3 Rostock Cornea Module, Heidelberg Engineering GmbH) at one week, one and three months and one year postoperatively. Ocular surface parameters like Schirmer test, tear film break up time and corneal sensations were also performed pre and postoperatively at one and three months. The results were significantly favouring the SMILE correction with sub-basal nerve density postoperatively at 11,870±8200 microns/mm² compared to 5770±3490 microns/mm² with FLEx. The ocular surface parameters were found to be significantly reduced, when FLex was compared with SMILE. This supports further the reduction in the sub-basal nerve density. The limitations of the study were low number sample size and lack of impression cytology to look at conjunctival goblet cells and their effect on ocular surface parameters. These results do add further to evidence that prove that SMILE is better than FLEx when treating myopia in a minimally invasive fashion.

Influence of femtosecond lenticule extraction and small incision lenticule extraction on corneal nerve density and ocular surface: A 1 year prospective, confocal, microscopic study.
Ishii R, Shimizu K, Igarashi A, et al.
JOURNAL OF REFRACTIVE SURGERY
2015;31(1):10-5.