title: Corneal flap displacement and drift in LASIK: comparison of Hansatome and Automated Corneal Shaper microkeratomes.
abstract: OBJECTIVE
  To describe and compare the displacement of corneal flaps created during laser in situ keratomileusis (LASIK) procedures performed with two different microkeratomes and analyze parameters (for example, pupil-to-hinge distance, drift during suction) that might affect the flap displacement or be influenced by flap displacement.
  
  
  METHODS
  This work was based on a cross-sectional study design.
  
  
  METHODS
  Images copied from video recordings of 206 consecutive LASIK surgeries were analyzed to determine the distance from pupil center to corneal flap hinge (pupil-to-hinge distance), the hinge size, the distance from the center of the pupil to the margins of the flap, and the positions of the suction ring before and after vacuum in corneal flaps created by the Hansatome and the Automated Corneal Shaper (ACS) microkeratomes. Accurate measurements of all these variables could be obtained in 121 eyes (Hansatome: n = 66, right eye (OD) = 27 eyes, left eye (OS) = 39 eyes; ACS: n = 55, OD = 25 eyes, OS = 30 eyes), which were included in the analysis. Formulas were derived to calculate from the measurements the magnitude and direction of the drift of the suction ring during vacuum and the final displacement of the corneal flap.
  
  
  RESULTS
  The mean +/- standard deviation (SD) drift of eyes during suction with the Hansatome was 0.27 +/- 0.02 mm and with the ACS was 0.12 +/- 0.02 mm (P <.001). The Hansatome induced, on average, more biased (temporal vs random) drift than did the ACS. The mean final displacement of the center of the flap from the center of the pupil was of equal magnitude for the two instruments (0.37 +/- 0.02 mm and 0.36 +/- 0.02 mm with the Hansatome and ACS, respectively).
  
  
  CONCLUSIONS
  The drift induced by the Hansatome contributes to the horizontal component of the final decentration of the corneal flaps. This tendency for drift and the resultant decrease in pupil-to-hinge distance should be considered to minimize flap displacements during LASIK.
authors.affiliation: Massachusetts Eye and Ear Infirmary, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02114, USA.
authors.forename: Rafael L
authors.initials: RL
authors.lastname: Ufret-Vincenty
authors.forename: Rogan
authors.initials: R
authors.lastname: Jiunn-Liang Chen
authors.forename: Dimitri T
authors.initials: DT
authors.lastname: Azar
mesh_terms: D003319:Corneal Stroma / Q000473:pathology*; D003430:Cross-Sectional Studies; D005123:Eye / Q000033:anatomy & histology; D006801:Humans; D007431:Intraoperative Complications / Q000175:diagnosis*; D020731:Keratomileusis, Laser In Situ / Q000009:adverse effects* / Q000295:instrumentation; D011680:Pupil; D054140:Refractive Surgical Procedures; D012189:Retrospective Studies; D013396:Suction; D013524:Surgical Flaps / Q000473:pathology*; D014741:Video Recording