title: Correction of myopia and astigmatism using an ablatable mask.
abstract: BACKGROUND
  Most excimer laser refractive procedures use a computer driven mechanical diaphragm to shape the laser beam. Studies are currently underway using an ablatable polymethylmethacrylate (PMMA) mask to transfer a new spherical or toric curve to the cornea for the correction of myopia and astigmatism; it may leave a smoother corneal surface than diaphragm procedures.
  
  
  METHODS
  As part of a Phase IIb FDA clinical study, 25 eyes of 25 patients underwent excimer laser photorefractive keratectomy using a hand held ablatable mask. Fifteen eyes had attempted spherical corrections of up to 6.00 diopters (D) and 10 had toric corrections of up to 6.00 D of sphere and 2.75 D of astigmatism.
  
  
  RESULTS
  Seventy-four percent of all eyes achieved uncorrected visual acuity of 20/40 or better--86% in the spherical group and 63% in the astigmatism group. Sixty-nine percent of eyes were within +/- 1 D of the attempted correction. In eyes treated for astigmatism, mean astigmatism decreased from 1.48 D preoperatively to 0.86 D postoperatively. Approximately one half of the eyes treated for astigmatism had a decrease in cylinder of more than 0.5 D. One eye lost 2 Snellen lines of best spherical corrected visual acuity. Video keratography showed toric ablations to result in an elliptical optical zone. Analysis of centration of the procedure showed 66% of ablations centered within 1.0 mm of the center of the pupil aperture.
  
  
  CONCLUSIONS
  The ablatable mask represents a promising modality for the treatment of eyes with both myopia and myopic astigmatism.
authors.affiliation: Department of Ophthalmology, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY 10467.
authors.forename: P S
authors.initials: PS
authors.lastname: Hersh
authors.forename: R
authors.initials: R
authors.lastname: Patel
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted; D053685:Laser Therapy / Q000295:instrumentation* / Q000379:methods; D008297:Male; D020366:Methylmethacrylate; D008768:Methylmethacrylates; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D011183:Postoperative Complications; D014481:United States; D014486:United States Food and Drug Administration; D014792:Visual Acuity
chemical_list: D008768:Methylmethacrylates; D020366:Methylmethacrylate