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SMILE yields stable visual, refractive outcomes at 3 years postop
Corrected distance visual acuity improved significantly, and 90% of eyes were within 1 D of targeted refraction at 3 years.
Small-incision lenticule extraction for high myopia resulted in stable long-term visual and refractive outcomes, despite a minor myopic regression in total corneal refractive power, a study found.
The procedure, known as SMILE, also yielded a significant long-term improvement in higher-order aberrations.
“We wanted to evaluate the long-term visual and refractive outcome after SMILE, as the longest reported follow-up time was 1 year when we began the study. Corresponding to the results, SMILE seems to have high predictability, efficacy and safety, with an increase in [corrected distance visual acuity] from 3 months to 3 years after operation. However, a minor myopic regression was observed in total corneal refractive power, although the subjective refraction remained stable,” Iben Bach Pedersen, MD, the corresponding author, told Ocular Surgery News.
Patients and parameters
The prospective study, published in the Journal of Refractive Surgery, included 87 eyes of 87 patients who underwent SMILE. All eyes had uncorrected distance visual acuity worse than 20/500 before surgery.
Surgery was performed with a 500 kHz VisuMax femtosecond laser (Carl Zeiss Meditec). Surgeons created a 6- to 6.5-mm diameter intrastromal lenticule under a 7.3-mm cap with a thickness of 110 µm to 120 µm. Peripheral lenticule thickness was 15 µm. A blunt spatula was inserted through a 30° to 60° peripheral incision to break the remaining tissue bridges. Forceps were used to remove the lenticule.
After surgery, patients were given chloramphenicol and fluorometholone drops four times daily for 1 week and then twice daily for 1 week.
Investigators assessed manifest refraction, logMAR uncorrected and corrected distance visual acuity, and corneal tomography at 3 months and 3 years after surgery.
The Pentacam (Oculus) was used to measure total corneal refractive power, central corneal thickness and root mean square of spherical aberration, coma and total higher-order aberrations.
The main outcome parameters were efficacy, predictability, safety and change in corneal aberrations, total corneal refractive power and spherical equivalent from 3 months to 3 years.
All 87 patients completed 3-month and 3-year follow-up examinations.
Results and conclusions
Average spherical equivalent was –7.3 D before surgery, –0.3 D at 3 months after surgery and –0.4 D at 3 years after surgery. The change between 3 months and 3 years was not statistically significant.
Mean uncorrected distance visual acuity was 0.04 logMAR at 3 months and 0.03 logMAR at 3 years after surgery; the change was not statistically significant. However, corrected distance visual acuity improved significantly from –0.05 logMAR at 3 months to –0.08 logMAR at 3 years (P < .001).
Uncorrected distance visual acuity was 20/20 or better in 58% of eyes at 3 months and 72% of eyes at 3 years.
Eighty-two percent of eyes were within 0.5 D of intended refraction and 93% of eyes were within 1 D at 3 months. At 3 years, 78% of eyes were within 0.5 D and 90% were within 1 D.
Spherical aberration and higher-order aberrations decreased significantly from 3 months to 3 years; coma did not change.
“It may be due to corneal remodeling that occurs years after surgery is performed,” Pedersen said.
Significant myopic regression was seen in total corneal refractive power but not in subjective refraction from 3 months to 3 years (P < .001).
Mean central corneal thickness increased from 448 µm at 3 months to 452 µm at 3 years; the increase was statistically significant (P < .001).
“[Corneal remodeling] may also be the reason why we observed a change in total corneal refractive power and a slight but significant increase in the central corneal thickness. It was essential to evaluate if myopic regression occurred, as earlier long-term studies of LASIK for myopia have shown significant regression years after surgery. But the regression in total corneal refractive power seems to have no influence in the subjective refraction, as we did not see any significant difference between 3-month and 3-year examinations,” Pedersen said. – by Matt Hasson
- Reference:
- Pedersen IB, et al. J Refract Surg. 2015;doi:10.3928/1081597X-20150923-11.
- For more information:
- Iben Bach Pedersen, MD, can be reached at Department of Ophthalmology, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, Denmark; email: iben.b.pedersen@gmail.com.
Disclosure: Pedersen reports no relevant financial disclosures.
Perspective
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This paper compares the 3-month postoperative results with the 3-year postoperative results in high myopia for SMILE. This study has some admitted selection bias, in that subjects were invited to the longer-term evaluation and only 87 of 106 eyes were available for this review, but if anything I believe this would be an unfavorable bias from this self-selection because those doing well might not want to bother with further examinations. The most important findings in this study were how remarkably stable the spherical equivalent was over this time period and the decrease in higher-order aberrations over that same time period. While there was some conflicting information such as an increase in corneal power over the same time despite the refractive stability, considering the high level of myopia treated, these results compare quite favorably to LASIK results in a similar population.
The practical consideration is that while LASIK is known to become less accurate at higher amounts of correction due to the additive nature of longer treatments creating more uncertainty in the results, in the case of SMILE, a single incision is responsible for the refractive correction, and the expectation is that it will maintain accuracy independent of the amount of correction, save for corneal remodeling effects. This makes SMILE well suited for all levels of refractive correction but particularly at higher corrections of sphere. One would hope that the same concept would hold true for cylinder corrections, but we do not yet have the data to evaluate higher amounts of cylinder, although in this study up to 2 D of cylinder was treated effectively. These results further support that SMILE has demonstrated itself to be a valuable addition to surgical methods for treating refractive error in clinical practice. SMILE is investigational and is not currently approved in the United States.