title: RGP contact lens fitting in keratoconus using FITSCAN technology.
abstract: OBJECTIVE
  To assess and compare the base curve (BC) of rigid gas permeable contact lens (RGP) that were calculated by FITSCAN using corneal topography (Orbscan IIz) and the diagnostic contact lens fitting method in keratoconus eyes.
  
  
  METHODS
  A prospective comparative study of 85 keratoconus eyes was conducted. Two masked observers calculated the contact lens parameters of RGP lens by diagnostic fitting method and using FITSCAN technology. The base curves calculated by two methods were compared using Wilcoxon signed rank test and agreement between two methods were analysed using Bland-Altman plot.
  
  
  RESULTS
  Eighty-five eyes from 55 keratoconus patients were included in the study. The mean age was 17.63±2.78 (range: 12-23) years and among them 46 were males. The keratoconus was graded into mild, moderate and severe based on average keratometry values. The base curve calculated by the FITSCAN is on average 0.22mm higher than that calculated by diagnostic method (P value <0.0001, 95% CI=0.155, 0.245, Wilcoxon signed rank test) and the bias between the two methods was found to be 2.7% (Bland-Altman plot), indicating systematic bias between the two modalities. By single linear regression analysis, the base curve of RGP contact lens could calculated by using the formula, base curve (BC)=(FITSCAN calculated BC×0.86563)+0.78738.
  
  
  CONCLUSIONS
  Our study showed that selecting the BC of the initial trial lens 0.22mm steeper than the FITSCAN calculated base curve, may help to reduce the complexity of RGP contact lens fitting in keratoconus.
authors.affiliation: L V Prasad Eye Institute, Hyderabad, India. mspreeji@gmail.com
authors.forename: Preeji S
authors.initials: PS
authors.lastname: Mandathara
authors.forename: Mariya
authors.initials: M
authors.lastname: Fatima
authors.forename: Sobia
authors.initials: S
authors.lastname: Taureen
authors.forename: Srikanth
authors.initials: S
authors.lastname: Dumpati
authors.forename: Mohd Hasnat
authors.initials: MH
authors.lastname: Ali
authors.forename: Varsha
authors.initials: V
authors.lastname: Rathi
mesh_terms: D000293:Adolescent; D001251:Astigmatism / Q000175:diagnosis* / Q000209:etiology / Q000534:rehabilitation*; D002648:Child; D003261:Contact Lenses; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D007640:Keratoconus / Q000150:complications / Q000175:diagnosis* / Q000534:rehabilitation*; D008297:Male; D017755:Prosthesis Fitting / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016037:Single-Blind Method; D012984:Software; D013813:Therapy, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D016896:Treatment Outcome; D014792:Visual Acuity; D055815:Young Adult