Binding affinity of benzalkonium chloride on contact lens surfaces and the effects on their physical properties

Benzalkonium chloride (BKC) is a cationic surfactant used as a component in ophthalmic eye drops. The effects of BKC on the eye and the simple binding of BKC on the contact lens surface have been reported in other studies. However, the exact value of the BKC binding affinity on the contact lens surfaces and its effects on the physical properties of contact lenses have not been studied. Here, the binding affinity of BKC toward two types of contact lenses, those with the wetting agent polyvinylpyrrolidone (PVP) and those without, was calculated. In addition, the refractive power, UV–vis transmittance, contact angle, water content, base curve, and diameter of the contact lenses after treatment with BKC were examined to evaluate the effects of its adsorption on the contact lens. We found that the maximum amount of adsorbed BKC was 2.88 mM for the contact lens without PVP whereas it was 2.32 mM for that with PVP. In contrast, the BKC binding affinities were similar. Crucially, the physical properties of the contact lens changed significantly because of the adsorption of BKC. Although BKC is a widely used preservative, our results suggest that use of PVP-containing contact lenses reduces BKC adsorption and discomfort.