Trillions of microorganisms (also referred to as microbiota or microbes) of thousands of different species comprise the microbiome inside of our bodies (Ursell et al, 2012). A typical human body harbors as many microbial species as human cells (Sender et al, 2016). The microbiome consists of bacteria, fungi, parasites, and viruses. These microorganisms coexist peacefully in healthy humans, primarily in the small and large intestines but also throughout the body. The microbiome is considered a supporting organ because of the daily functions that it performs in the operations of the human body. Each person has a unique network of microbiota that is determined by DNA (www.hsph.harvard.edu/nutritionsource/microbiome ).

The eye hosts a core microbiome limited to four genera of bacteria: Staphylococci, Diphtheroids, Propionibacteria, and Streptococci. In addition, the torque teno virus, found in some intraocular diseases, is part of the core and is present on the ocular surface in 65% of healthy people (St. Leger, 2019). The ocular microbiome is dependent on age, geographical region, ethnic background, contact lens wear, and disease state (St. Leger, 2019).

A healthy ocular surface has a relatively stable microbiome with nominal diversity (Ozcan and Willcox, 2019). Ocular surface bacteria help maintain homeostasis by modulating immune function. Researchers have investigated the effect of contact lens wear and ocular disease on ocular surface and eyelid microbiota and the immunoregulatory role of ocular surface microbiota; compositional changes in microbiota occur in ocular surface conditions such as dry eye, blepharitis, and trachoma (Ozcan and Willcox, 2019).

The Effect of Care Solutions

A recent study performed a microbiome analysis of contact lens care solutions and tear fluids of contact lens wearers (Hotta et al, 2020). Molecular biology techniques were used to assay contact lens care solutions in lens storage cases and tears from subjects who had allergic symptoms related to lens wear. Fifteen contact lens storage cases were collected and analyzed from subjects who had allergic symptoms (n = 9) and from a control group of healthy, asymptomatic lens wearers (n = 6). Bacterial populations in care solutions and tears were assayed by culture and 16S rDNA sequencing. High-performance liquid chromatography was used to measure tear histamine levels. In subjects who had allergic symptoms, western blot analysis was performed to identify bacteria recognized by tear IgE.

Compared to asymptomatic subjects, the abundance of Gram positive bacteria in the microbiomes of contact lens care solutions used by those who had allergic symptoms were higher using detailed population analysis (42.24% ± 9.47% versus 16.85% ± 22.76% abundance) (Hotta et al, 2020). In allergic subjects, tear microbiome analysis revealed that the abundance of Streptococcus was significantly higher than in other subjects (19.02% ± 5.50% versus 3.08% ± 3.35%, P < 0.01). In all subjects who had allergic symptoms, tear IgE reacted with Streptococcus (100%), but not with Staphylococcus (Hotta et al, 2020).

The findings provide insight into the pathogenesis of allergic symptoms and identify Streptococcus as an important aspect of allergic symptoms associated with lens wear.

This study brings up questions of future formulations for contact lenses and solutions. Will it be possible to personalize a lens care solution based on an individual’s microbiome? Can a person’s microbiome be used to create a customized contact lens? Can contact lens discomfort and dropout be eliminated or reduced with personalized contact lenses? Creating a fairly stable ocular microbiome for contact lens wearers may augment the lens-wearing experience. CLS

For references, please visit www.clspectrum.com/references and click on document #302.