[Impact of Different Percent Tissue Altered Values on Visual Outcome after Refractive Small Incision Lenticule Extraction (ReLEx SMILE)].

Purpose  To compare the visual outcomes after ReLEx SMILE treatment of eyes with low and high PTA values (PTA: percent tissue altered) within a follow-up period of up to 3 years and to assess whether a high PTA value might contribute to the development of keratectasia, as is the case for LASIK. Methods  This retrospective analysis comprises results from 313 eyes (189 patients) with a PTA value of less than 40 % and of 373 eyes (213 patients) with a PTA value of at least 40 %. Preoperatively and up to 3 years after SMILE surgery, refraction values, monocular corrected (CDVA) and uncorrected distant visual acuity (UDVA) and wavefront data were evaluated. Results  One to 3 years after surgery, the group with PTA < 40 % (PTA ≥ 40 %) had a loss of two Snellen lines in 1.1 % (0.0 %) of the cases. Loss of one line occurred in 1.1 % (3.6 %) of the eyes, whereas 97.7 % (96.4 %) remained unchanged or gained lines. With respect to predictability of the spherical equivalent, 92.0 % (78.6 %) of the eyes were within ± 0.5D and 97.7 % (92.9 %) were within ± 1.0D. The group with high PTA values displayed a slightly but significantly greater undercorrection of about 0,25D. 74.4 % (71.8 %) achieved UDVA of at least 20/20 and 96.5 % (87.1 %) achieved at least 20/25. The mean UDVA was - 0.03 ± 0.10logMAR (0.01 ± 0.12logMAR) and its mean difference to the preoperative CDVA was 0.00 ± 0.09logMAR (0.03 ± 0.12logMAR). Conclusion  ReLEx SMILE is a safe and effective corneal refractive treatment, even for PTA values of 40 % and more. Eyes with high PTA values did not display any evidence of keratectasia development within the 3-year follow-up of this study.