Long-term observation of SMILE gives better myopia prognosis

Today, small incision lenticule extraction (SMILE) is very common. Despite this, while more than 750,000 procedures have been completed internationally,¹ only a few clinics in the world have recorded observations of more than five years.

The stability of the refractive correction is one of the most important indicators in refractive surgery, which is why my colleagues and I evaluated the stability, safety, efficacy and predictability of SMILE in patients who underwent the procedure in 2011. By comparing postoperative results at 12 months with those at 5 years, we now have a long-term prognosis for patients who undergo SMILE.

12-month trial

My colleagues and I were included in the first investigative clinical trial of SMILE in 2011, wherein we reported the 1-year refractive results, contrast sensitivity, higher-order aberrations (HOA) and complications after SMILE. We evaluated 54 eyes of 27 patients who had a mean spherical equivalent of -4.68 ± 1.29 D and who underwent SMILE by the same surgeon using a femtosecond laser system (Visumax, Carl Zeiss Meditec AG).

We followed these patients for 1 year beginning with follow-up visits at 1 day, 1 week, and 1, 3, 6 and 12 months postoperatively. Our parameters were uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), contrast sensitivity and wave front measurements, in addition to recording all complications.

Suction loss occurred in one eye during the procedure, so we were able to gather the 12-month results on 53 eyes. After 1 year, 88% of eyes with plano target had a UDVA of 20/20 or better. Twelve percent of eyes lost one Snellen line of CDVA, 31% gained one Snellen line and 3% gained two Snellen lines.

The mean spherical equivalent (SE) after 1 year was -0.19 ± 0.19, while the mean refraction change between month one and 12 was 0.08 D. We did not observe any visually threatening complications. In this first cohort of SMILE patients, the refractive results were satisfactory.²

Five-year trial

The purpose of our most recent investigation was to report the 5-year results of patients by evaluating the first 42 fully seeing eyes treated with SMILE for myopia and myopic astigmatism in 2011 and 2012. We analysed stability, safety, efficacy and predictability, and as an added component we explored the patient’s subjective satisfaction with the treatment.

This prospective clinical trial comprised 100 eyes from 50 patients who underwent SMILE in 2011 and 2012. The mean age was 29 years with 79% being female and 21% male. Preoperatively, the patients had a mean SE of -4.56 D ±1.29 D, a mean sphere of -4.36 D ±1.31 D and a mean cylinder of -0.41 D ±0.51 D.

The technique and parameters for the laser included topical anaesthesia, a scanning direction for the bottom of the lenticule from the periphery to the centre, and a “cap” that was created from the centre to the periphery. The optical zone was from 6 to 7 mm, and the cap diameter was 0.5-1 mm more than the lenticule.

Minimal thickness was 15 мк and the cap thickness was 120 мк. Residual stroma was at least 300 мк, and the incision width was 3 to 4 мм. Follow-up occurred at 1 day; 1 week; 1 month; 3 months; 6 months; 12 months; and subsequently, 5 years.

At the 5-year follow-up, 42 eyes from 21 patients were available. We found that the mean sphere moved from -0.15 to -4.35 and spherical equivalent was -0.23 from a range of 0.38 to -0.35. There was minimal degradation.

When we looked further into this we found that 10 of 32 eyes had a small progression of myopia while the other eyes were stable. Topography revealed no changes, and emmetropia was in between 0.25 D in 71% of patients.

At the 12-month visit as well as the 5-year visit, visual acuity remained at 90%. BCVA was high at 4.8% in 2012, and in 5 years no patient lost any Snellen lines, which was better than 1, 3, 6, and 12 months; 12% gained two lines in 5 years. The results of the patient questionnaire reflected that 40% of patients experienced glare, 55% experienced a slight problem with night driving, and 95% found that their vision had significantly improved.

Additional findings

A few other clinics have observed patients close to the 5-year mark and they have found similar results. Han, et al. investigated the long-term refractive outcomes, wavefront aberrations and quality of life after SMILE in patients with moderate to high myopia.

Twenty-six patients (47 eyes) with a preoperative mean SE of -6.30 ± 1.47 D underwent SMILE. Measurements included UDVA, CDVA, manifest refraction, wavefront aberrations and quality of life. At 4 years postoperatively, UDVA was better than or equal to 20/20 in 92% of eyes.

The efficacy index was 1.07 ± 0.16, and 89% of eyes were within ± 0.5 D of the intended refractive target. No eyes lost Snellen lines, and the safety index was 1.16 ± 0.14. There were no significant changes of SE during postoperative evaluations at 1, 3 and 6 month visits or 1, 2 and 4 year visits.

HOA, coma and spherical aberration all increased postoperatively, and there were no significant changes of aberrations detected in the 37 eyes that were analysed at 1-month, 6-month or 4-year follow-ups. Furthermore, those who underwent SMILE revealed a significantly higher score on quality of life than those in the spectacle group (45.71 ± 2.61 versus 39.96 ± 3.56, P < 0.001).³

In the first long-term study of SMILE, Blum et al. also evaluated the 5-year results of SMILE in patients with myopia and myopic astigmatism. In 2008 and 2009, 91 eyes were treated. Fifty-six out of 91 eyes of the original treatment group volunteered for re-examination 5 years after surgery. UDVA and CDVA were measured after 5 years along with objective and manifest refractions.

They also evaluated the interface and corneal surface by slit lamp examination and documented complications, such as corneal scars, corneal ectasia, persistent dry eye symptoms or cataract. After 5 years, there were no significant changes to the 6-month data. SE was -0.375 D and close to target refraction (emmetropia).

Thirty-two of the 56 eyes had gained one to two Snellen lines, but there was no loss of two or more lines over the 5-year period. Long-term regression was recorded at 0.48 D. SMILE proved to be an effective, stable and safe procedure for the treatment of myopia and myopic astigmatism.⁴

Conclusion

Measuring parameters, such as stability following refractive procedures, allows us to follow fluctuations in refraction over time. Analysing accuracy is also an opportunity to assess for a fall in emmetropia because of correction.

Additionally, reviewing efficacy allows us to compare acuity DCVA before surgery. It is the most important indicator that shows the patient’s satisfaction with the result of the operation.

Long-term observation of SMILE reveals high stability at various degrees of correction of myopia. This allows surgeons who apply this method of treatment to give patients a long-term prognosis.

Our research shows that in comparison with other, well-known methods like LASIK or PRK, the SMILE method demonstrates an unchanged result for many years. For now, few eyes have been subjected to such a long period of observation, but since this surgery is widely used all over the world, further observations will allow SMILE to take its place in modern refractive surgery.

References
 

1. Zeiss press release; 2017. Available at: https://www.zeiss.com/meditec/us/media-and-news/latest-news/zeiss-showcases-smile-swept-source-biometry-with-the-barrett-suite-at-ascrs-2017.html. Accessed August 14, 2017.

2. Sekundo W, Gertnere J, Bertelmann T, Solomatin I. One-year refractive results, contrast sensitivity, high-order aberrations and complications after myopic small-incision lenticule extraction (ReLEx SMILE). Graefes Arch Clin Exp Ophthalmol. 2014;252:837-843.

3. Han T, Zheng K, Chen Y, Gao Y, He L, Zhou X. Four-year observation of predictability and stability of small incision lenticule extraction. BMC Ophthalmol. 2016;16:149.

4. Blum M, Täubig K, Gruhn C, Sekundo W, Kunert KS. Five-year results of Small Incision Lenticule Extraction (ReLEx SMILE). Br J Ophthalmol. 2016;100:1192-1195. doi: 10.1136/bjophthalmol-2015-306822. Epub 2016 Jan 8.

Dr Jana Gertnere, MD

E: janager@balticom.lv

Dr Jana Gertnere is a specialist in refractive pathology at Dr Solomatin Eye Center, Riga, Latvia. Dr Gertnere has no financial interest in the products or companies mentioned.

Dr Igor Solomatin

E: acucentrs@acucentrs.lv

Dr Igor Solomatin is a professor of ophthalmology, Latvian state University and practices at Dr Solomatin Eye Center, Riga, Latvia. Dr Solomatin has no financial interest in the products or companies mentioned.