title: A simplified method to perform photorefractive keratectomy using an erodible mask.
abstract: BACKGROUND
  Photorefractive keratectomy (PRK) using the current erodible mask technique is difficult to perform, because of the stringent requirements in the alignment of the eye to the mask and in the centration of the mask under the laser beam. The surgeon has to manually control the eye-cup over 5 degrees of freedom. If not accurately done this may lead to decentration of the ablation and bring about technical problems during treatment. The aim of this study was to find a way to improve and simplify the erodible mask procedure.
  
  
  METHODS
  We used a modified non-contact mask eye-cup with a rigid mechanical support to obtain a precise and reliable positioning in space of the mask itself. Eye centration over the pupillary aperture was obtained with conventional patient fixation on the reference aiming light, coaxial to the laser beam path, and controlled using two He-Ne beams aimed at the corneal apex.
  
  
  RESULTS
  Good reliability was demonstrated in the first 22 eyes operated on using this technique. All the masks were ablated with good centration of the laser beam over the polymethylmethacrylate (PMMA) button, and all the treatments were satisfactorily centered over the pupillary aperture. No complications or side effects were encountered during the treatments.
  
  
  CONCLUSIONS
  Compared to the conventional erodible mask procedure, this technique proved much faster to perform, was more comfortable for both patient and surgeon, and was technically easier for the operator.
authors.affiliation: Department of Ophthalmology and Visual Sciences, S. Raffaele Hospital, University of Milan, Italy.
authors.forename: P G
authors.initials: PG
authors.lastname: Gobbi
authors.forename: F
authors.initials: F
authors.lastname: Carones
authors.forename: F
authors.initials: F
authors.lastname: Scagliotti
authors.forename: E
authors.initials: E
authors.lastname: Venturi
authors.forename: R
authors.initials: R
authors.lastname: Brancato
mesh_terms: D003315:Cornea / Q000601:surgery*; D006801:Humans; D053685:Laser Therapy / Q000295:instrumentation* / Q000379:methods*; D020366:Methylmethacrylate; D008768:Methylmethacrylates; D009216:Myopia / Q000601:surgery*; D015203:Reproducibility of Results
chemical_list: D008768:Methylmethacrylates; D020366:Methylmethacrylate