title: Association Between Corneal Deformation and Ease of Lenticule Separation From Residual Stroma in Small Incision Lenticule Extraction.
abstract: OBJECTIVE
  To study the association between corneal deformation (CD) and ease of lenticule separation from the stroma in small incision lenticule extraction.
  
  
  METHODS
  Thirty-six myopic eyes of 36 patients underwent small incision lenticule extraction. Preoperative refraction, intraocular pressure, central corneal thickness, and CD were evaluated with Scheimpflug imaging and air-puff applanation. Fourier transform of CD waveform was also performed. The surgeon also graded the ease of separation of lenticule surfaces from the residual stroma intraoperatively as grades 1 (low effort), 2 (moderate effort), and 3 (high effort). All the procedures were performed by the same surgeon. CD values were concealed from the surgeon. Differences between the grades were assessed with 1-way analysis of variance and analysis of covariance.
  
  
  RESULTS
  Mean preoperative refraction, intraocular pressure, central corneal thickness, lenticule thickness, and incision width were similar among the grades (P > 0.05). A total of 5 of the 10 analyzed CD variables were significantly different among the grades. Among them, deformation amplitude (1.20 vs. 1.13 vs. 1.07 mm in the order of increasing grades, P = 0.001), velocity of the corneal apex at the second applanation point (-0.47 vs. -0.43 vs. -0.40 m/s, P = 0.02), peak distance (5.33 vs. 5.25 vs. 5.07 mm, P = 0.006), area under the deformation amplitude (13.40 vs. 12.84 vs. 12.06, P = 0.04), and root mean square of Fourier coefficients (0.12 vs. 0.12 vs. 0.11 mm, P = 0.005) decreased from grades 1 to 3.
  
  
  CONCLUSIONS
  CD was inversely correlated with the ease of lenticule separation from the residual stroma and may assist in customization of the energy parameters of the laser.
authors.affiliation: *Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India; †Vice-Chairman, Narayana Nethralaya, Bangalore, India; and ‡Imaging, Biomechanics and Mathematical Modeling Solutions, Narayana Nethralaya, Bangalore, India.
authors.forename: Rohit
authors.initials: R
authors.lastname: Shetty
authors.forename: Luci
authors.initials: L
authors.lastname: Kaweri
authors.forename: Natasha
authors.initials: N
authors.lastname: Pahuja
authors.forename: Kalyani
authors.initials: K
authors.lastname: Deshpande
authors.forename: Maithil
authors.initials: M
authors.lastname: Thakkar
authors.forename: Abhijit
authors.initials: A
authors.lastname: Sinha Roy
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D003319:Corneal Stroma / Q000503:physiopathology / Q000601:surgery*; D048988:Corneal Surgery, Laser / Q000379:methods*; D003430:Cross-Sectional Studies; D004548:Elasticity / Q000502:physiology*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008866:Microsurgery / Q000379:methods; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D011446:Prospective Studies; D014792:Visual Acuity / Q000502:physiology