title: Vector analysis of astigmatic correction after small-incision lenticule extraction and femtosecond-assisted LASIK for low to moderate myopic astigmatism.
abstract: OBJECTIVE
  To compare astigmatic correction between femtosecond-assisted laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE).
  
  
  METHODS
  A total of 111 patients were included in this prospective study. Fifty-seven eyes were treated with LASIK and 54 eyes were treated with SMILE for myopia with low to moderate (-0.25 to -4.0 D) astigmatism. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity and manifest refraction were measured preoperatively and at 1 and 3 months postoperatively. Visual and refractive outcomes were reported. Changes in refractive astigmatism were evaluated using vector analysis.
  
  
  RESULTS
  Preoperative characteristics were similar between both groups. The UDVA at 1 and 3 months was better in the LASIK group compared with the SMILE group (p<0.009). Postoperative cylinder was higher in the SMILE group (p<0.001). Fewer eyes attained the attempted cylindrical correction in the SMILE group (p<0.029). Vector analysis showed no significant difference in target-induced astigmatism (p=0.091) and angle of error (p>0.596) between the two groups. Surgically induced astigmatism was significantly lower in the SMILE group (p<0.023), while the difference vector (p<0.001) and absolute angle of error (p<0.016) were significantly higher in the SMILE group. No significant difference was found in these parameters between 1 and 3 months in both groups (p>0.122).
  
  
  CONCLUSIONS
  Our results showed that SMILE offered a less favourable astigmatic correction comparable to femtosecond-assisted LASIK in eyes with low to moderate myopic astigmatism. The alignment of treatment was more variable in SMILE, leading to a lower efficacy compared with LASIK by 3 months postoperatively.
authors.affiliation: Department of Ophthalmology, Hong Kong Eye Hospital, Kowloon, Hong Kong Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Kowloon, Hong Kong.
authors.forename: Tommy C Y
authors.identifier: http://orcid.org/0000-0003-4228-9482
authors.initials: TC
authors.lastname: Chan
authors.affiliation: Department of Ophthalmology, The University of Hong Kong, Hong Kong, Hong Kong.
authors.forename: Alex L K
authors.initials: AL
authors.lastname: Ng
authors.affiliation: Hong Kong Laser Eye Center, Hong Kong, Hong Kong.
authors.forename: George P M
authors.initials: GP
authors.lastname: Cheng
authors.affiliation: Department of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Kowloon, Hong Kong.
authors.forename: Cong
authors.initials: C
authors.lastname: Ye
authors.affiliation: Hong Kong Laser Eye Center, Hong Kong, Hong Kong.
authors.forename: Victor C P
authors.initials: VC
authors.lastname: Woo
authors.affiliation: Department of Ophthalmology, Hong Kong Eye Hospital, Kowloon, Hong Kong Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Kowloon, Hong Kong.
authors.forename: Clement C Y
authors.initials: CC
authors.lastname: Tham
authors.affiliation: Department of Ophthalmology, Hong Kong Eye Hospital, Kowloon, Hong Kong Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Kowloon, Hong Kong Centre for Eye Research Australia, University of Melbourne, Victoria, Australia.
authors.forename: Vishal
authors.initials: V
authors.lastname: Jhanji
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery*; D003315:Cornea / Q000503:physiopathology; D003319:Corneal Stroma / Q000601:surgery*; D048988:Corneal Surgery, Laser / Q000379:methods*; D019781:Corneal Topography; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology; D016896:Treatment Outcome; D014792:Visual Acuity / Q000502:physiology
keywords: Treatment Lasers