Silicone hydrogel contact lenses may significantly limit absorption of certain anti-infective agents used to treat ocular surface diseases such as infectious keratitis, reports a new study in the September 2015 Eye & Contact Lens.1 Interactions between contact lenses and topical drugs have become a much-examined topic in recent years, as lenses are known to stimulate biochemical changes that alter the composition of the ocular surface and tear film.2,3 This can lead to issues with drug effectiveness. Additionally, when used in conjunction with topical drops, therapeutic soft contact lenses may also act as a physical barrier to topical drug absorption and contribute to formula dilution by trapping debris underneath.

Researchers from the University of Pittsburgh School of Medicine performed a biological assay to determine the activity of diffused moxifloxacin, polyhexamethylene biguanide (PHMB) and amphotericin B (AmB) against Staphylococcus epidermidis and Saccharomyces cerevisiae. Results indicated sufficient diffusion of moxifloxacin and PHMB at 30 minutes, but not AmB. Ultimately, however, only moxifloxacin demonstrated efficacy at the 60-minute mark, and at 10 times the amount of the most common commercial formulation; thus, the researchers say, further study is needed.  

1. Zambelli AM, Brothers KM, Hunt KM, et al. Diffusion of antimicrobials across silicone hydrogel contact lenses. Eye & Contact Lens. Sept. 2015;41(5):277-280. 
2. Mann A, Tighe B. Contact lens interactions with the tear film. Exp Eye Res 2013;117:88-98.
3. Craig JP, Willcox MD, Argueso P, et al. The TFOS International Workshop on Contact Lens Discomfort: Report of the contact lens interactions with the tear film subcommittee. Invest Opthalmol Vis Sci. 2013:54:TFOS123-TFOS156.