Dynamics of Soft Contact Lens-Surface Wettability in vitro: Effect of Surface-Active "Leachables"

Abstract

Purpose: : To investigate the release of surface-active substances from soft contact lenses and their influence on lens-surface wettability in vitro.

Methods: : Wettability of the contact lenses immersed in OptiFree® (OF) lens-care solution (LCS) was evaluated in dynamic-cycling regime using modified captive-bubble apparatus. The advancing and receding angles (CA) were measured concurrently with surface tension. Conventional pHEMA-based lenses (e.g., Accuvue2, BioMedics55, Proclear, Extreme H₂O), and silicone hydrogel (SiH) lenses (FocusN&D (FND), O₂Optix, PureVision (PV), Biofinity, Accuvue Oasys, and Accuvue Advance) were studied. After measurements with pristine lenses from blister, lenses were soaked in 20 ml of LCS each and agitated overnight. Contact angles and surface tension were measured for 7 consecutive days. Surface tension of blister-pack solutions was measured by pendant drop method.

Results: : Surface tension of blister-pack solutions ranged from 38 (Extreme H₂O) to 70 mN/m (O₂Optix and PV), lower than that of OF (71.4 mN/m). Lens-surface wettability of AV2 and BM55, gauged by aqueous adhesion energy (E_adh) , was reduced by 35-40 mN/m after 7 days of soaking. For SiH-lenses (FND, O₂Optix, and PV), changes in E_adh were within 15 mN/m after prolonged soaking. Other SiH-lenses contained surface-active ingredients from blister-pack solutions, and reduction of air-aqueous surface tension by up to 20 mN/m was observed upon equilibration. Pristine SiH lenses exhibited a wide spectrum of E_adh from 8 mN/m (PV) to slightly above 50 mN/m (Biofinity and O₂Optix); the advancing CA were ranging from 12.8±4.5^o (Biofinity) to 16.4±7.5^o (AV Oasys) and 34.9±3.5^o (AV Advance), to 36±2.4 ^o and 44±4.1^o (O₂Optix, FND), and up to 83±15.1 ^o (PV). For all the lenses, the receding angles were below 15^o and were not affected by leachables.

Conclusions: : The surface-active ingredients of blister solutions or of lens-matrixes affected wetting properties of all studied SCLs, although in different extent. Surface tension reduction caused by leachables lowered the advancing contact angles on most pristine SCLs. SiH lenses exhibited stable and self-sustained in vitro surface wettability. For most conventional lenses, surface wettability was largely dependent on leachables and reduced significantly after depletion of leachables.

Keywords: contact lens