title: Preoperative assessment of corneal and refractive stability in soft contact lens wearing photorefractive candidates.
abstract: OBJECTIVE
  This pilot study compared traditional methodologies; manifest refraction and keratometry, with that of newer technologies; corneal topography, and optical pachymetry, in assessing corneal and refractive stabilization after soft contact lens wear in photorefractive candidates. The timeline differences among these various technologies in determining refractive and corneal stability were investigated.
  
  
  METHODS
  This was a masked prospective observational clinical study of full-time soft contact lens subjects on various wear schedules, all eligible candidates for photorefractive surgery. Subjects discontinued contact lens wear within 30 min of the initial study visit. During each study visit, the same sequence of tests were performed (manifest refraction, keratometry, corneal topography, and optical pachymetry). The timing of the last visit was determined when the four procedures resulted in stable findings when compared with the previous visit.
  
  
  RESULTS
  Fifteen soft contact lens wearers and five noncontact lens wearing controls completed the study. The mean number of days until stability of the 15 test subjects were: 10.7 +/- 10.4 days with manifest refraction, 16.2 +/- 17.5 days with keratometry, 28.1 +/- 17.7 days with topography, and 35.1 +/- 20.8 days with pachymetry. Within the control group, intraclass correlation coefficients for all four methods were > or =0.89, indicating very little variability. Analysis with the randomized block design found statistical differences between traditional and newer technologies in their assessment of stability (p < 0.001). One-way Analysis of variance of the various soft contact lenses modalities suggested extended hydrogel wearers taking the longest time to reach stability after discontinuing full-time contact lens use.
  
  
  CONCLUSIONS
  Corneal curvature and thickness measurements took the longest to achieve consistency. Thus, topography and pachymetry may be better methods to determine ocular stability before photorefractive surgery. In light of this finding, the current protocol in practice of determining the readiness of contact lens candidates for photorefractive surgery may be inadequate.
authors.affiliation: Southern California College of Optometry, Fullerton, California 92831, USA. lng@scco.edu
authors.forename: Loretta T
authors.initials: LT
authors.lastname: Ng
authors.forename: Eunice Myung
authors.initials: EM
authors.lastname: Lee
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Nguyen
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D003262:Contact Lenses, Extended-Wear; D003263:Contact Lenses, Hydrophilic; D003315:Cornea / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery*; D019781:Corneal Topography; D005260:Female; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D054018:Lasers, Excimer; D008297:Male; D018903:Photorefractive Keratectomy; D010865:Pilot Projects; D011300:Preoperative Care; D011446:Prospective Studies; D012029:Refraction, Ocular
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate