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 +/- 0.10 logMAR (0.01 +/- 0.12 logMAR) and its mean difference to the preoperative CDVA was 0.00 +/- 0.09 logMAR (0.03 +/- 0.12 logMAR). 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.