This study found that the incidence of dry eye was significantly lower after small incision lenticule extraction (SMILE) compared with LASIK.
This is likely because the SMILE procedure requires less surgical alteration of the cornea. While LASIK results in destruction of sub-basal nerves due to flap cutting, SMILE extracts a deeper stromal segment of tissue through a smaller incision.
This was a nonrandomized, prospective study that included 60 age-, sex- and refraction-matched patients who underwent bilateral myopic surgery; evenly divided between the 2 procedures.
There was a high incidence of mild to moderate dry eye disease in both groups 1 month after surgery, which remained significantly higher in the LASIK group at 6 months (P < 0.01).
At 6 months, more SMILE patients did not use artificial tears (80% vs. 57%), while 20% of LASIK patients required daily and frequent use of tear drops or gels.
Data also indicated that SMILE had a less deleterious effect on the ocular surface and corneal innervation.
Corneal sensitivity, based on the Cochet–Bonnet esthesiometer, was significantly lower at 1 month in the LASIK group, whereas no significant difference between the groups was found at 6 months. Using confocal microscopy to evaluate the sub-basal nerve plexus, they showed that the nerve density, number of long nerve fibers and nerve branchings in the SMILE group were statistically superior to those in the LASIK group 1 month and 6 months after surgery.
Additionally, the density of dendritic cells at the corneal surface was significantly greater in the LASIK group compared with the SMILE group 1 month and 6 months postoperatively. The density of activated keratocytes was significantly lower in the LASIK group 1 month postoperatively but not statistically different from the SMILE group at 6 months.
The authors say more study is required to determine if SMILE is appropriate for individuals with low- to mild-severity dry eye, particularly the many contact lens wearers who suffer from dry eye and are not good candidates for LASIK.