title: Surface roughness in PMMA is linearly related to the amount of excimer laser ablation.
abstract: OBJECTIVE
  To determine if surface roughness after excimer laser ablation is a function of the amount of ablation and to identify a standard unit for ablation roughness.
  
  
  METHODS
  We used a VISX 20/20 excimer laser to perform a series of single zone 6-mm diameter ablations (photorefractive keratectomy [PRK]) in polymethylmethacrylate (PMMA). Corrections ranged from -1.00 diopter (D) to -15.00 D. A scanning white light interferometry microscope (Zygo Corp, Middlefield, Conn) was used to quantify the surface roughness at the center of each ablation.
  
  
  RESULTS
  We found a linear increase in surface roughness as the refractive correction increased. Each diopter increment resulted in an approximately 300 nm increased peak-to-valley measurement. This represented an increase of 25 nm roughness per micron of ablation in PMMA.
  
  
  CONCLUSIONS
  Surface irregularities in PMMA increase with ablation depth. We propose a unit of measure of roughness, the "ablation," expressed as the peak-to-valley distance in nm/divided by m of ablation.
authors.affiliation: O'Donnell Eye Institute, St. Louis, MO 63122, USA.
authors.forename: C B
authors.initials: CB
authors.lastname: O'Donnell
authors.forename: J
authors.initials: J
authors.lastname: Kemner
authors.forename: F E
authors.initials: FE
authors.lastname: O'Donnell
mesh_terms: D006801:Humans; D053685:Laser Therapy / Q000379:methods; D007834:Lasers; D008768:Methylmethacrylates / Q000528:radiation effects*; D008857:Microscopy, Interference; D054140:Refractive Surgical Procedures; D013499:Surface Properties
chemical_list: D008768:Methylmethacrylates