title: Which soft lens power is better for piggyback in keratoconus? Part II.
abstract: OBJECTIVE
  To evaluate how soft lens power affects rigid gas-permeable (RGP) lens power and visual acuity (VA) in piggyback fittings for keratoconus.
  
  
  METHODS
  Sixteen keratoconus subjects (30 eyes) were included in the study. Piggyback contact lens fittings combining Senofilcon-A soft lenses of -6.00, -3.00, +3.00 and +6.00 D with Rose K2 RGP contact lenses were performed. Corneal topography was taken on the naked eye and over each soft contact lens before fitting RGP lenses. Mean central keratometry, over-refraction, RGP back optic zone radius (BOZR) and estimated final power as well as VA were recorded and analyzed.
  
  
  RESULTS
  In comparison to the naked eye, the mean central keratometry flattened with both negative lens powers (p<0.05 in all cases), did not change with the +3.00 soft lens power (p=1.0); and steepened with the +6.00 soft lens power (p=0.02). Rigid gas-permeable over-refraction did not change significantly between different soft lens powers (all p>0.05). RGP's BOZR decreased significantly with both positive in comparison with both negative soft lens powers (all p<0.001), but no significant differences were found among negative- or positive-powers separately (both p>0.05). Estimated RGP's final power increased significantly with positive in comparison with negative lens powers (all p<0.001), but no significant differences were found among negative or positive lens powers separately (both p>0.05). Visual acuity did not change significantly between the different soft lens powers assessed (all p>0.05).
  
  
  CONCLUSIONS
  The use of negative-powered soft lenses in piggyback fitting reduces RGP lens power without impacting VA in keratoconus subjects.
authors.affiliation: MRG Doctores S.C, Madrid, Spain. Electronic address: mrjlentes@gmail.com.
authors.forename: Miguel
authors.initials: M
authors.lastname: Romero-Jiménez
authors.affiliation: Menicon R&DIC, Menicon Co., Ltd, Japan.
authors.forename: Jacinto
authors.initials: J
authors.lastname: Santodomingo-Rubido
authors.affiliation: Clinical & Experimental Optometry Research Lab, Center of Physics, University of Minho, Braga, Portugal.
authors.forename: Jose-Manuel
authors.initials: JM
authors.lastname: González-Meijóme
authors.affiliation: Pontificia Universidad Católica de Valparaíso, Chile.
authors.forename: Patricia
authors.initials: P
authors.lastname: Flores-Rodriguez
authors.affiliation: European University of Madrid, Spain.
authors.forename: Cesar
authors.initials: C
authors.lastname: Villa-Collar
mesh_terms: D000328:Adult; D003263:Contact Lenses, Hydrophilic; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007640:Keratoconus / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D017755:Prosthesis Fitting; D014792:Visual Acuity; D055815:Young Adult
keywords: Contact lens; Cornea; Keratoconus; Keratometry; Piggyback