Preventing amblyopia

SMILE is as effective as LASIK, easier for anisometropic children

Howard Larkin

Posted: Wednesday, May 1, 2019

Reduced pain and dry eye after surgery make small-incision lenticule extraction (SMILE®) an attractive alternative to femto-LASIK for preventing amblyopia in anisometropic children who cannot tolerate patches or contact lenses, Mohamed MK Diab MD told the 2018 World Society of Paediatric Ophthalmology and Strabismus Subspecialty Day in Vienna.

At first glance, performing corneal refractive surgery on very young patients seems like a mistake destined to cause problems as the children grow and their refractions change, Dr Diab noted. However, for severely anisometropic children, correcting the refractive imbalance early can prevent a far worse fate – amblyopia. For young children who cannot tolerate eye patches or contact lenses, refractive surgery may be the best available option, he added.

Due to its refractive efficacy and painlessness relative to surface ablation, femto-LASIK has been the corneal procedure of choice for treating young children. However, the less-invasive SMILE procedure offers several potential advantages over LASIK including less pain, dry eye and injury risk due to flap dislocation after surgery.

But is SMILE as effective and stable as LASIK over the long-term? To find out, Dr Diab and colleagues at Magrabi Eye Hospital in the Asser region of Saudi Arabia conducted a prospective study to evaluate how SMILE visual outcomes compare with femto-LASIK six years after surgery.

The study compared 105 eyes undergoing SMILE with 98 eyes undergoing femto-LASIK. SMILE procedures utilised a 6.5mm diameter lenticule with a 7.5mm cap and minimum thickness of 15 microns. All eyes were tested in follow-up for refractive efficacy, dry eye, optical aberrations and corneal biomechanics. Patient questionnaires evaluated dry eye symptoms, comfort and recovery time.

Concerning safety, refractive predictability and efficacy, there was no statistically significant difference between the two groups, Dr Diab reported. One year after surgery, mean uncorrected visual acuity was -0.01±0.11 logMAR in the SMILE group and 0.02±0.12 in the femto-LASIK group.

Both means remained stable at five years with -0.01±0.12 logMAR in the SMILE group and 0.05±0.13 in the femto-LASIK group.

However, SMILE performed better in several other areas, Dr Diab noted. For one, wavefront aberrometry using the Topcon KR-1W showed significantly lower total higher-order aberrations induced in the SMILE group than in the LASIK group.

This finding is consistent with other SMILE-LASIK comparisons, which have found a wider proportion of the optical zone in SMILE v LASIK, at about 80 and 69% respectively.

For another, minimal pain and postoperative discomfort resulted in higher patient satisfaction in the SMILE group. The smaller incision and lack of a flap that must be carefully cared for after surgery may help explain these findings.
SMILE showed a clear advantage over femto-LASIK in dry eye. Schirmer’s test, tear film break-up time, corneal sensitivity and corneal regeneration all favoured SMILE, Dr Diab said. These results may be explained by the fact that the smaller SMILE lenticule cut of 2.0mm-to-3.0mm may leave more corneal surface nerves intact than a 20mm or so LASIK flap. However, Dr Diab noted both procedures prevent deep stromal nerves from reaching the surface.

Since Bowman’s layer and the anterior lamellae remain intact after SMILE, the procedure may preserve corneal biomechanical strength better than LASIK, which is especially important for younger patients, Dr Diab said. However, the literature on this effect includes conflicting reports and is not conclusive.

No significant changes were noted in endothelial cell density in the SMILE group, Dr Diab reported.
“Five years after surgery, ReLEx® SMILE and femto-LASIK show equally good results in terms of safety, predictability and efficacy. However, no dry eyes were observed in the SMILE group compared to the femto-LASIK group.

“Therefore, we clearly favour the ReLEx SMILE technique in patients who ask for painless refractive correction,” Dr Diab concluded.