Dry Eye Dx and Tx
Biofilms and the Ocular Surface
BY KATHERINE M. MASTROTA, MS, OD, FAAO
Early in our lives, bacteria from the environment colonize our conjunctiva, corneal surface, and associated tissues including the eyelid and lacrimal systems. It is estimated that more than 200 species of bacteria commonly inhabit the human conjunctival mucosa (Dong et al, 2011). The ocular surface is chock-full of nutrients to sustain resident bacteria; in fact, in a balanced and intact ocular surface system, commensal bacterial species may protect the ocular surface from pathogenic infection (Miller and Iovieno, 2009).
When Bacteria Change Form
I imagine that when most of us think about bacteria from the eye, we envision bacterial isolates cultured from the cornea or conjunctiva growing on agar plates. Or, we envision independent, floating microorganisms swimming in the tide of the tear film. Mobile and free-floating bacteria are called the “planktonic” form. Interestingly, the life cycle of most bacteria is in sessile aggregates: microbes most often construct and live in a complex, film-like meshwork known as a biofilm.
Costerton et al (1999) defined biofilm as a structural community of bacterial cells enclosed in a self-produced polymeric matrix that can adhere to inert or living surfaces. The biofilm environment provides physical protection to bacteria and also allows them to communicate with each other (quorum sensing), which may lead to an increase in virulence and propensity to cause infection (Kievit and Iglewski, 2000). In addition, when bacteria change from being planktonic to biofilm-forming, they undergo changes in gene expression; there is speculation that such alterations create a more virulent strain of the bacteria or cause a conversion from a commensal species to a more harmful form (Bjarnsholt, 2013).
With the constant physical disruption of blinking, tear exchange, tear anti-microbial agents, and enzymes and mucins, bacteria generally face a robust ocular surface defense system that prevents generating a biofilm. However, when abiotic surfaces such as contact lenses, ocular prostheses, corneal sutures, and punctal plugs are introduced, biofilm formation upon them becomes a greater concern.
The Importance of Lid Hygiene
Considering the above, it seems intuitive that appropriate lid hygiene practices are in order to lessen the bacterial load on the eyelid/margin and eyelashes, aiding the natural ocular surface defense mechanisms. I often refer to Professor Benitez-Del-Castillo (2012), who suggests that eyelid hygiene should be incorporated into a broader concept of eyelid health in which eyelid cleansing is part of a more complete program of care that includes screening and risk assessment, patient education, and coaching.
I recommend, and most patients prefer, commercially prepared lid hygiene products. Most of these are available as foaming cleansers or pre-moistened wipes.
New to the lid/eyelash cleanser list is NovaBay Pharmaceutical’s i-Lid Cleanser, a bottled, liquid solution containing Neutrox (pure hypochlorous acid). Hypochlorous acid, with antimicrobial and anti-inflammatory activity, is naturally produced by host white blood cells to defend against pathogenic microorganisms. Additionally, in-office removal of eyelid/lash debris and de-bulking microbial load and biofilms can be achieved with Rysurg LLC’s instrument BlephEx, which mechanically debrides treated surfaces.
Take Preventive Measures
There is much to learn about biofilm ecology and how it relates to bacterial virulence. In the meantime, it would seem prudent to clear away bacteria of concern before pathology sets in. CLS
For references, please visit www.clspectrum.com/references and click on document #229.
Dr. Mastrota is secretary of the Anterior Segment Section of the American Academy of Optometry. She is a consultant or advisor to Allergan, B+L, BioTissue, Nicox, NovaBay Pharmaceuticals, and OcuSoft and is a stock shareholder of TearLab Corporation. Contact her at email@example.com.