Effect Of Combined Small Incision Lenticule Extraction And Collagen Cross-Linking (Smile Xtra) On The Posterior Cornea

• To compare the effects of combined small incision lenticule extraction and collagen cross-linking (SMILE Xtra) versus SMILE on the posterior cornea.

Keye Eye Center, Seoul, Korea

• This was a retrospective review of 222 eyes with SMILE Xtra and 195 eyes with SMILE from January 1, 2021, to December 31, 2023, at the Keye Eye Center, Seoul, Korea.
• Preoperative biometric data, including axial length(AXL), white to white(WTW), central corneal thickness(CCT), flat K, steep K, sphere(S), cylinder(C), spherical equivalent(SE), were collected.
• The Spherical equivalent(SE), uncorrected distance visual acuity(UDVA) and corneal back elevation difference were evaluated at postoperative months 1, 3, 6 and 12.

• No difference in age(26.29±5.87years vs 26.31±6.69years; P=0.980), sex distribution(male 51.8% vs male 51.0%), AXL(26.02±0.86mm vs 26.05±1.30mm; P=0.802), WTW(11.64±0.37mm vs 11.69±0.43mm; P=0.218), CCT(540.07±16.55㎛ vs 537.42±29.07㎛; P=0.248), SE(-5.57±1.07D vs -5.82±1.98D; P=0.100) between SMILE and SMILE Xtra were observed.
• There was no difference in SE, UDVA between groups at baseline and postoperative months 1, 3, 6 and 12.
• There was no difference in the center value of preoperative back elevation difference in SMILE and SMILE Xtra (6.04 ± 3.27 vs 6.45 ± 3.74; P=0.233), but the center value of postoperative back elevation difference showed a significant difference between the two groups(4.90 ± 3.85 vs 3.98 ± 3.90; P=0.038).

• Study results suggest that patients at risk of corneal ectasia can be considered safe to perform surgery with SMILE Xtra.