title: The effect of lens wear on refractive index of conventional hydrogel and silicone-hydrogel contact lenses: a comparative study.
abstract: OBJECTIVE
  The purpose of this work was to evaluate the ability of four silicone-hydrogel contact lenses (galyfilcon A, balafilcon A, lotrafilcon A and lotrafilcon B) to retain their equilibrium water content before and after wear, through measurements of refractive index and compare with that of a conventional disposable hydrogel contact lens (etafilcon A).
  
  
  METHODS
  The refractive indices of 115 contact lenses were measured using an automated refractometer (CLR 12-70, Index Instruments, Cambridge, U.K.) before and after a schedule of daily wear by 58 patients for 30 days in the case of silicone-hydrogel lenses and 15 days for the conventional contact lenses.
  
  
  RESULTS
  In the silicone-hydrogel contact lenses the changes on the refractive indices were not statistically significant, however after being worn the refractive index of the conventional etalfilcon A hydrogel contact lens increased significantly (p<0.001).
  
  
  CONCLUSIONS
  The results presented here show that after being worn the silicone-hydrogel contact lens, show more capacity to retain or to reach their initial equilibrium water content than conventional hydrogel contact lenses. This suggests that the silicone-hydrogel contact lenses are less susceptible to spoilation over time maintaining its biocompatibility and contributing to the clinical success of lens performance.
authors.affiliation: Center of Physics (Optometry), School of Sciences, University of Minho, Portugal. mlira@fisica.uminho.pt
authors.forename: M
authors.initials: M
authors.lastname: Lira
authors.forename: L
authors.initials: L
authors.lastname: Santos
authors.forename: J
authors.initials: J
authors.lastname: Azeredo
authors.forename: E
authors.initials: E
authors.lastname: Yebra-Pimentel
authors.forename: M E C D
authors.initials: ME
authors.lastname: Real Oliveira
mesh_terms: D003261:Contact Lenses; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D020100:Hydrogels; D008297:Male; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000175:diagnosis* / Q000534:rehabilitation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012825:Silicon; D016896:Treatment Outcome
chemical_list: D020100:Hydrogels; D012825:Silicon