Quantitation of cholesterol and phospholipid sorption on silicone hydrogel contact lenses

Abstract

The introduction of silicone hydrogel (SiHy) contact lenses to the consumer marketplace necessitates study of the susceptibility of these lenses to spontaneous deposition by hydrophobic lipid components of ocular tears. The use of radioisotopes to measure lipid sorption on SiHy contact lenses gives precise and accurate results but requires institutional infrastructure and compels efficient lipid removal from the lens. This study compares three methods of quantitating phospholipid and cholesterol sorption on SiHy lenses using radiolabeled cholesterol and phosphatidylcholine that were sorbed on lenses from an artificial tear fluid. A triple extraction technique using n-propanol gives the most reliable results. Comparison of sorption on SiHy lenses shows that balafilcon A and senofilcon A lenses sorb similar amounts, while lotrafilcon B lenses sorb comparatively less.

The role of multi-purpose solutions in prevention and removal of lipid depositions on contact lenses

“…This suggests that the ATF was consistent from batch to batch. Recognizing that small changes in ATF composition and preparation procedure may have an impact on lipid sorption [19,20], we present this data as a study of trends and differences pertaining to lens type and MPS type, not actual amounts of lipid predicted after one day of wear and one night of soaking in an MPS.…”

“…This composition has higher values of lipid and lower values of lactoferrin and lysozyme than found in ATF formulations from other labs. It was selected because it produces lipid deposits on SiHy lenses after overnight incubation in similar amounts to those found on clinically worn lenses after several weeks of wear [16,17]. It is known that lipid sorption is sensitive to ATF preparation and composition [18,19].…”

“…The extraction procedure is detailed in a prior publication [16]. In brief, each lens was placed in a 20-mL glass scintillation vial containing 2 mL of n-propanol and placed on a rotary table shaker at 60 rpm for 1 h at 37 • C. Each lens was then held above the extraction solution with plastic tweezers and rinsed with 1 mL of n-propanol into the same vial.…”

“…The details of preparing the ATF were reported in a previous publication [16]. Briefly, the aqueous base of the ATF, borate buffered saline (BBS), was prepared by mixing boric acid, sodium borate and sodium chloride in distilled deionized water (DDH2O), and the pH of the solution was adjusted to 7.3 through addition of NaOH or HCl.…”

Ex Vivo Analysis of Cholesterol Deposition for Commercially Available Silicone Hydrogel Contact Lenses Using a Fluorometric Enzymatic Assay

“…10 For example, in an in vitro study by Carney et al, 16 lotrafilcon A and B contact lenses absorbed the lowest levels of cholesterol compared with senofilcon A, galyfilcon A, and balafilcon A. 8,19,22,23 However, each method has limitations, such as its sensitivity, accuracy, or efficiency. However, the use of artificial tear solutions does not accurately mimic the diversity of the tear film and may not be representative of the clinical situation.…”