title: Comparison of higher-order aberration and optical quality after Epi-LASIK and LASIK for myopia.
abstract: BACKGROUND
  Epipolis laser in keratomileusis (Epi-LASIK) and laser in situ keratomileusis (LASIK) are two main surgical techniques for myopia in refractive surgery at present. However, the visual outcome and optical quality after the two procedures are not clear. We conducted the current prospective study to compare ocular higher-order aberrations and evaluate optical quality after Epi-LASIK and LASIK.
  
  
  METHODS
  Sixty-two eyes were included. Thirty-two eyes were treated using Epi-LASIK and thirty eyes using LASIK. Best-corrected visual acuity, uncorrected visual acuity, manifest refraction, and wavefront aberrations were measured and analyzed preoperatively and 4-6 months postoperatively. Wavefront aberrations were measured by Wavescan (VISX, Santa Clara, CA, USA) using a Hartmann-Shack sensor.
  
  
  RESULTS
  The mean changes in RMS for the 5th order (S(5)) were 0.022 ± 0.009 µm and 0.050 ± 0.010 µm, which was significantly smaller in the Epi-LASIK group than in the LASIK group for a 6-mm pupil (P = 0.048, analysis of covariance). The mean changes in C (5) (-1) and C (5) (5) were significantly smaller in the Epi-LASIK group than in the LASIK group at both 3-mm and 6-mm pupil sizes (P = 0.027, 0.045 and 0.024, 0.027, analysis of covariance). Also, the changes in the contribution of coma-like and spherical-like aberration at 6-mm pupil size were statistically significantly different after both procedures (P = 0.000, randomized block design analysis of covariance).
  
  
  CONCLUSIONS
  Both Epi-LASIK and LASIK show their own characteristics in increased higher-order aberration at smaller and larger pupil sizes, and may create different effects on optical quality for photopic (smaller pupil) and scotopic conditions (larger pupil). We speculate that the visual performance in the Epi-LASIK group may be better than in the LASIK group for the larger pupil size.
authors.affiliation: Tianjin Eye Hospital, Clinical College of Ophthalmology, Tianjin Medical University, No 4, Gansu Rd, Heping District, Tianjin, 300020, China.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Yang
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.forename: Kanxing
authors.initials: K
authors.lastname: Zhao
authors.forename: Lihua
authors.initials: L
authors.lastname: Fang
mesh_terms: D057128:Aberrometry; D000293:Adolescent; D000328:Adult; D003315:Cornea / Q000503:physiopathology*; D057108:Corneal Wavefront Aberration / Q000175:diagnosis / Q000503:physiopathology*; D005500:Follow-Up Studies; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult
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