Purpose: Silicone hydrogel contact lens spoliation has been shown to be predominantly associated with lipids. Post wear contact lens lipid uptake has been measured as a means of characterising silicone hydrogel resistance to lipid spoliation. The limitation of the current techniques are that lipids are extracted from the worn contact lenses without differentiation between bulk and surface lipids, whereas from a clinical viewpoint the important parameter is surface spoliation. The current study describes a novel method to measure lipid uptake differentiating between bulk and surface lipids.<br />
Methods: A sandwich method was developed which involved contact under controlled force of the contact lens back and front surfaces with filter paper to transfer the lipids available at the contact lens surface. Chloroform / methanol extraction was applied to the two filter papers and to the contact lens and the extracts were analysed by HPLC with ELSD detection. The method was validated for both hydrogel (Hy) (etafilcon A & nelfilcon A) and silicone hydrogel (SiHy) (balafilcon A, lotrafilcon B, senofilcon A) materials by loading three samples per material with lipid standards. Confirmation measurements were subsequently made with ex vivo, worn contact lenses (SiHy n=6; Hy n =3).
Results: The results obtained showed that: (i) SiHy uptake of standard lipids was more than twice Hy uptake (mean 49.3µg vs. 23.4µg). (ii) Lipid partition for SiHy and Hy was different: For SiHy, bulk lipid was dominant (69.7%) and surface lipid was low (Front 17.0% - Back 13.3%); however, for Hy, surface lipid was dominant (Front 34.3% - Back 38.5%) and bulk lipid relatively low (27.3%). (iii) The applicability of the technique to worn contact lenses was confirmed, the same relative uptake being observed with ex vivo lenses (Total uptake: SiHy 21.0µg, Hy 9.5µg; Front: SiHy 17.6%, Hy 46.3%; Bulk: SiHy 62.2%, Hy 20.2%; Back: SiHy 20.3%, Hy 33.4%).
Conclusions: This novel technique differentiates between surface and bulk lipid uptake in vitro and ex vivo. The findings demonstrate vastly different lipid partitioning for SiHy, (bulk lipid) and Hy (surface lipid) suggesting that comparing overall lipid uptake is not a true depiction of contact lens lipid interaction in vivo, where surface lipids are responsible for lens spoliation, and explaining the reason for the poor correlation to date between lipid uptake and comfort
|Number of pages||1|
|Journal||Investigative Ophthalmology and Visual Science|
|Publication status||Published - 1 Jun 2015|