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.