One of our biggest fears as optometrists is irreversible vision loss due to contact lens-related infections. We try and try to explain to our patients the importance of removing their contacts nightly and not wearing them beyond the manufacturers’ recommendations, but we all know that these recommendations are not always followed even with the best of intentions.
New advancements in antimicrobial contact lenses are a way to limit contact lens-related infections and thus preserve our patients’ vision.
Contact lens stats
An article by the CDC in 2015 estimated that approximately one in six adults (>18 years old) wears contact lenses. Ninety-nine percent of those wearers exhibited at least one behavior that put them at greater risk of microbial keratitis. As we all well know, contact lens wearers are at increased risk of infection if they sleep in their lenses, expose lenses to water, fail to replace disinfecting solution daily, or fail to change contact lens cases at least every three months.
The incidence of microbial keratitis in RGP wearers is 2/10,000. For daily-wear soft CL wearers, the incidence is 2.2-4.1/10,000/year and 13.3-20.9/10,000 per year for extended-wear soft contact lens wearers. The majority of corneal ulcers were caused by Gram negative bacteria.
Antimicrobial contacts
Coating medical devices with an antimicrobial layer, in many cases made of heavy metals, is done in many areas of medicine to prevent infection (think catheters or orthopedic devices). The idea of coating a contact lens or case with an antimicrobial layer has been investigated for decades.
The goal is to either coat a lens or infuse it with a compound that can minimize microbial colonization and biofilm formation, thereby reducing the risk of infection and inflammation. It is important that at the same time these lenses do not disrupt the normal ocular flora.
So, it’s an exciting development to think of contact lenses that could be coated with an antimicrobial biofilm to help prevent infection and, thereby, reduce unnecessary vision loss.
Several types of antimicrobial contact lenses have been produced over the years, although many have not progressed to human trials.
For example, silver and selenium have both been embedded in contact lenses. These did not make it to market either due to corneal toxicity or lack of efficacy in decreasing corneal infiltrative events. Within the last few years, melamine, a peptide found in our innate immune system, has been tested to reduce microbial colonization in contact lens wear.
A recent study looked at etafilcon A contact lenses (Acuvue 2) coated with a derivative of the peptide melamine called “Mel4” to determine whether they can reduce the incidence of microbial corneal infiltrative events (CIEs) during extended wear. One hundred seventy-six participants were randomized to wear a Mel4 coated antimicrobial contact lens in one eye and an uncoated Acuvue 2 lens in their contralateral eye and instructed to replace lenses biweekly for a period of three months.
Corneal infiltrative events included microbial keratitis (MK) as well as “significant events” (CLARE), contact lens peripheral ulcers (CLPUs) or infiltrative keratitis (IK). “Non-significant” events that were tracked included asymptomatic infiltrates or asymptomatic IK. During the three-month study, nine participants experienced CIE, three from the Mel4-coated group and six in the control group.
While this shows that half the number of participants in the Mel4 group had CIEs compared with the control group, this was not statistically significant.
Image 1: Extracted from Efron Grading Scale, The Vision Institute
One person in the Mel4 group, however, wore the contact lens for longer than the prescribed period of time (22 days instead of the prescribed 14). Even removing this person, there was a 69% reduction in incidence of CIEs for Mel4-coated lenses, but this was also not statistically significant (P=0.29).
After a CIE was discovered, the lenses were placed in sterile saline and cultured and participants’ eyes were swabbed for analysis. Four of the nine contact lenses where CIE occurred did not show any microbial growth. Lid swabs of participants wearing control lenses showed coagulase-negative staphylococci while, interestingly, none of the lids from eyes wearing Mel4-coated lenses grew any microbes.
This study had some limitations especially in that their small sample size only had a small number of patients who experienced CIE in either group, which did not allow for statistical significance. Additionally, according to the study, approximately 50% of contact lens wearers worldwide wear silicone hydrogel lenses, while the lenses tested in this study were etafilcon A, an older lens material.
Conclusion
While this study showed initial promise, further studies will be needed to move Mel4-coated contact lenses into the consumer market. Those studies will need to focus on larger sample size and testing silicone hydrogel lenses.
Antimicrobial contact lenses offer exciting potential to further reduce the incidence of vision loss from microbial keratitis in patients worldwide. Be sure to keep an eye out as this exciting technology continues to develop.
