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To evaluate 2-year efficacy, safety and predictability of SMILE Xtra in patients with abnormal topography, low residual stromal bed(RSB) thickness, higher refractive error and thin pre-operative central corneal thickness(CCT). Also, to find out the safety and clinical effect of Xtra energy protocol in different patient subgroups.
Patients with moderate risk according to the Randleman ectasia score who had undergone SMILE Xtra from March 2016 to March 2017 were collected and retrospectively reviewed. Study group was divided into 4 subgroups and clinical outcomes were analyzed(group A;abnormal topography, group B;RSB thickness<300um, group C;spherical equivalent>-9.5D or lenticule thickness>130um, group D;pre-operative CCT<510um). For Xtra protocol, 90 seconds of 0.25% Rivoflavin soaking followed by 60 seconds of UV-A radiation of 30mW/cm2 was done. Uncorrected distant visual acuity, corrected distant visual acuity, manifested refraction, topography and specular microscopy were checked pre and postoperatively.
Pre-operative mean spherical equivalent(SEQ) was -7.01±2.03D and mean CCT was 535.3±28.1um for SMILE Xtra patients. Post-operative visual acuity of SMILE versus SMILE Xtra at day 1 was 0.94±0.15 versus 0.80±0.22, however, it was 1.12±0.22 versus 1.08±0.21 at 2-year. Efficacy index was comparable(1.16 versus 1.13). Safety index for SMILE Xtra group was 1.16, and it showed good predictability(R2= 0.985). Mean endothelial cell count difference before and after SMILE Xtra with 1.8J/cm2 energy protocol was 45.6±121.1 but there was no statistical significance. Comparison of visual and refractive outcomes showed no significant differences within subgroups.
Long-term visual outcomes of SMILE Xtra showed comparable results. Safety or predictability was not affected by combined crosslinking with 1.8J/cm2 energy protocol. Different subtype characteristics did not affect the final clinical results. Thus, SMILE with accelerated cross-linking may be an effective and safe strategy for moderate risk patients.