Fiona Patricia Carney

The ocular surface, the tear film, and the wettability of contact lenses.

The tear film is the interface between the ocular surface and the external environment and, as such, plays several important roles.1 (i) It forms a refracting thin film that smooths out the irregular corneal surface topography. (ii) It maintains an extracellular environment for the epithelial cells of the cornea and the conjunctiva that is fairly constant in terms of pH, oxygen and carbon dioxide levels, and nutrient and growth factor concentrations. (iii) Tears dilute and wash away noxious stimuli, including bacteria, which are also combated by an elaborate and effective antibacterial system. (iv) The tear film changes its composition in response to physiological stimuli.

Contact Lenses and Tear Film Interactions

Contact lenses are a successful form of vision correction. However, under certain circumstances adverse inflammatory responses can occur during lens wear. These inflammatory responses can be divided into those that involve the cornea and conjunctiva, and those that are primarily conjunctival. The former category includes microbial keratitis, contact lens-induced acute red eye, contact lens-induced peripheral ulcers, infiltrative keratitis, asymptomatic infiltrative keratitis and asymptomatic infiltrates. These conditions have recently been described in detail, and many are produced by bacterial contamination of contact lenses.1-4 The major contact lens-related inflammatory conditions primarily associated with the conjunctiva are contact lens-induced papillary conjunctivitis (CLPC), and the more severe form of this disease, giant papillary conjunctivitis (GPC). However, the etiology of these conditions is poorly understood. The aim of the current study is to examine the effect of contact lens wear on tear proteins and determine which and how much specific tear proteins are adsorbed to the contact lens during wear.

In vitro adsorption of tear proteins to hydroxyethyl methacrylate-based contact lens materials.

Objectives: Investigations of polymer interactions in single protein solutions is a necessary step in the elucidation of in vivo early binding events during protein deposition on hydroxyethyl methacrylate-based contact lens materials. Quantity and tenacity of binding of significant tear components to groups I and IV contact lenses was assessed. Competitive binding by these components was also examined. Methods: Adsorption on FDA groups I and IV hydrogel lenses was monitored using 125I-labeled protein. Lenses were incubated in increasing concentrations of radiolabeled single species proteins in solution. For competition experiments, concentration of each radiolabeled protein was held constant and the adsorption/sorption challenged with increasing concentrations of nonlabeled proteins. Lenses were soaked in phosphate-buffered saline to determine desorption. Results: Group IV lenses bound large amounts of lysozyme, whereas group I lenses bound highest amounts of albumin. Albumin binding to both lens types was relatively strong and could not be competed from binding by other proteins lysozyme, lactoferrin, and mucin. Mucin at high concentrations tended to positively cooperate with the binding of lactoferrin and albumin to all lenses. Conclusions: Binding of proteins to hydroxyethyl methacrylate-based hydrogel lens surfaces is affected by charge and polymer components, and perhaps manufacturing processes. Albumin binds strongly to lens surfaces, and this may play an adverse role during contact lens wear.