title: Factors that influence in vitro cholesterol deposition on contact lenses.
abstract: OBJECTIVE
  The purpose of this study was to analyze the impact that incubation time, lipid concentration, and solution replenishment have on silicone hydrogel (SiHy) and conventional hydrogel (CH) contact lens cholesterol deposition via in vitro radiochemical experiments.
  
  
  METHODS
  Four SiHy (senofilcon A, lotrafilcon B, comfilcon A, balafilcon A) and two CH (etafilcon A and omafilcon A) contact lenses were incubated in an artificial tear solution (ATS) that contained major tear film proteins, lipids, salts, salts, and a trace amount of radioactive C-cholesterol. Lenses were incubated for various incubation times (1, 3, 7, 14, or 28 days), with three concentrations of lipid (0.5×, 1×, 2× tear film concentration) and with or without solution replenishment to assess each variable's impact on cholesterol deposition. After incubation, the lenses were extracted using 2:1 chloroform:methanol, extracts were analyzed in a beta counter and masses (micrograms per lens) were extrapolated from standard curves.
  
  
  RESULTS
  Within the SiHy materials, balafilcon A deposited the greatest amount of cholesterol (p < 0.001) and lotrafilcon B the lowest (p < 0.001). The CH lens materials showed significantly lower uptake amounts than any of the SiHy lens materials (p < 0.001). The uptake of cholesterol ranged from 0.01 ± 0.01 μg/lens to 3.22 ± 0.34 μg/lens for all lens materials. Kinetic uptake of cholesterol was shown to be continuous throughout the 28 days of incubation without plateau (p < 0.001), and varying the lipid concentration did impact the resulting cholesterol deposition (p < 0.001). Replenishing the ATS every other day also affected cholesterol deposition throughout the experiment. Overall, the deposition pattern was 2× > replenishing > 1× > 0.5×.
  
  
  CONCLUSIONS
  Overall, SiHy lenses deposit significantly more cholesterol than CH lens materials, and the mass of lipid deposited is dependent on the contact lens material, length of incubation, concentration of lipids in the ATS, and the replenishment of ATS.
authors.affiliation: *MSc †PhD, FAAO ‡MPS §PhD, FCOptom, FAAO Centre for Contact Lens Research, School of Optometry and Vision Science, University of Waterloo (HW, HL, MH, LK, LWJ) Waterloo, Ontario, Canada and Department of Chemical Engineering, McMaster University (HL), Hamilton, Ontario, Canada.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Walther
authors.forename: Holly
authors.initials: H
authors.lastname: Lorentz
authors.forename: Miriam
authors.initials: M
authors.lastname: Heynen
authors.forename: Lise
authors.initials: L
authors.lastname: Kay
authors.forename: Lyndon W
authors.initials: LW
authors.lastname: Jones
mesh_terms: D002784:Cholesterol / Q000378:metabolism*; D003263:Contact Lenses, Hydrophilic; D005136:Eye Proteins / Q000378:metabolism; D020100:Hydrogels; D066298:In Vitro Techniques; D008055:Lipids; D009883:Ophthalmic Solutions; D011485:Protein Binding; D011506:Proteins; D012828:Silicones; D012996:Solutions
chemical_list: D005136:Eye Proteins; D020100:Hydrogels; D008055:Lipids; D009883:Ophthalmic Solutions; D011506:Proteins; D012828:Silicones; D012996:Solutions; C523195:balafilcon A; C540498:comfilcon A; C524582:lotrafilcon B; C523196:senofilcon A; C042434:tear proteins; D002784:Cholesterol