My colleagues and I conducted a retrospective multicenter study from four centres in Germany and Austria. We included 43 eyes out of 1,963 eyes. There was a retreatment rate of 2.2%, and three patients were excluded due to loss of follow-up.
In the study, 40 eyes were included with a follow-up of at least 3 months. Manifest refractive spherical equivalent (MRSE) before SMILE was 6.35 diopters and 0.86 before PRK. The target was, in every case, plano refraction.
For two-thirds of the cases, we used the advanced ablation algorithm (AAA) profile from the MEL 90 Excimer Laser platform (Carl Zeiss Meditec); in 20% of the cases, we used tissue saving ablation (TSA) profile; in 7% we used the topographic guided profile; and in 5% the aberration smart ablation (ASA) profile.
The mean refractive surgery equivalent showed a significant reduction after 1 week and remained stable for up to 3 months at 0.03 diopters.
In this group, before the PRK treatment, 27.5% were within 0.5 diopters, improving up to 80% after PRK. Seventy-five percent were within 1.0 diopter, improving to 92.5% and 25% of the patients were over 1.0 diopter refractive error, improving down to 7.5%, which was a significant improvement.
In addition, the uncorrected visual acuity showed a significant improvement at 6 weeks and remained stable up to 3 months at a level of 0.08 LogMAR. The corrected distance visual acuity after 6 weeks was equal to corrected distance visual acuity preoperatively, which is average. However, we had some outliners, so there was some loss of lines. Fifteen percent lost one line, and no patients lost more than one line (see Figure 1).
Interestingly, of the 15% of patients who lost one line, two-thirds achieved the best visual acuity of 20/20. They came from 20/18 to 20/20 and one-third was 20/25. No patient was below 20/25 after PRK.
The safety index was 1.06. We had one significant haze after PRK, showing resolution after 3 months of topical steroid medication. There were some unsatisfactory refractive outcomes in the form of two major undercorrections. One patient showed –1.75. This was the patient with the highest spherical equivalent pre-SMILE, and we did enhancement after 4 months.
Another patient was approximately -1.0 diopter, and the enhancement was done after 4 months as well, which was perhaps too close to the initial procedure.
There were two overcorrections, including 1.75 and 1.38 diopters, both with the ASA profile, which indicates that the ASA profile is not suitable for touchup-procedures. To compare the ablation profiles, AAA, TSA and topographic-guided are almost identical and no statistically significant difference between the profiles were found.
Surface ablation combined with a mitomycin C application seems to be safe and effective to treat residual refractive errors after SMILE. Due to low residual refractive errors, the ASA profile is not recommended due to the tendency of overcorrection. Of course, long-term results are necessary to compare it to different and other touch-up techniques as secondary SMILE and LASIK.