Kendra Krutilla
Graduate Student, Ph.D. Program
University of Pittsburgh
B.S. Chemical and Petroleum Engineering, minor in Bioengineering, 2001
Research Interest:
Modification of soft contact lenses both to improve the wettability of the lens regarding the pre-lens tear film and to minimize contact lens-cornea adhesion
Research Summary:
Title: Soft Contact-Lens Surface Phenomena: wettability enhancement, tear-film stability, fouling, and bacterial adhesion.
Wettability Enhancement
Many clinicians and researchers believe that reducing the liquid-contact angle of soft contact lenses can improve pre-lens tear-film stability leading to better wearing comfort. Unfortunately, the contact angles of commercially available contact lenses are not ideal. With this in mind, many contact-lens care solutions now contain poly(ethylene oxide)-poly(propylene oxide) block-copolymer surfactants which act as wetting agents. These wetting agents significantly reduce the contact angle of some soft contact lenses.
We hypothesize that the efficacy of these wetting agents is dependent upon the ability to both adsorb onto the surface and absorb into the polymer matrix of the soft contact lenses and slowly release during wear. Using a modified captive-bubble technique and tensiometry, we examine these two mechanisms of sorption and the kinetics of desorption of two such wetting agents, Tetronic 1304 and Pluronic F127, from two soft contact lens brands, Acuvue 2 and O2 Optix. Our findings support our hypothesis and indicate that enhanced wetting can be achieved for several days when the wetting agent both adsorbs onto and absorbs into the lens.
Tear-Film Stability
As mentioned previously, theory teaches us that improved wettability should relate to improved tear-film stability. The use of Tetronic 1304 with Acuvue 2 contact lenses results in an ideal wetting angle, which should result in ideal tear-film stability. To test this theory, w e performed a clinical study to investigate the correlation among the contact angle of lenses with and without wetting agents, tear-film stability, and comfort. Our findings indicate the in-vitro contact angle as measured by the captive-bubble technique does not correlate to either tear-film stability or comfort. However, we did find that the contact angles of the contact lenses after wear were statistically equivalent despite having significantly different contact angles before contact with the human eye. Our hypothesis is that upon insertion of the lens into the eye, tear-film components adsorb to the surface of the lens, which changes the wettability of the lens. We therefore conclude that it is not the “fresh” contact angle that dictates tear-film stability, but the contact angle after adsorption of tear-film components.
Fouling
Because it is unreasonably expensive to perform clinical trials to simply test tear-film component adsorption to and the resulting wettability of contact lenses, an in-vitro simulation of fouling would be beneficial. To meet this demand, we devised an in-vitro blink-cycle cell that mimics contact-lens exposure to the human-eye environment during blinking and that permits contact-angle assessment. Evaluation of the cell shows that when all tear-film components (lipids, proteins, salts, and mucin) are included the contact angles of the lenses placed in the blink-cycle cell are equivalent to lenses worn by humans.
Bacterial Adhesion
The most serious complication of soft contact-lens wear is microbial infection of the cornea. It is imperative that contact lenses not foster growth of bacterial colonies on their surfaces. We have designed a constant-shear flow cell to expose contact lenses to bacteria and can then enumerate the amount of bacteria on the lens surface using either microscopy or a viable cell count. We test lenses that have been exposed to various wetting agents or fouled in our blink-cycle cell as well as commercially available clean lenses.