The Ocular Microbiome, Inflammaging, and Surface Health

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Introduction Our eyes are covered by a thin film of tears and a community of harmless microbes – the ocular surface microbiome – that help protect them. This microbiome normally lives in balance, but as we age the balance shifts. Aging brings a chronic, low-level inflammation (often called “inflammaging” ()) which can affect all tissues, including the eyes. The result is a higher risk of conditions like dry eye and meibomian gland dysfunction (MGD) – where the oil glands in the eyelids don’t work well. These conditions cause tear film instability and irritation. In recent years, researchers have found that age-related changes in the eye’s microbial community are linked to this inflammation and surface disease. Understanding these changes is important for keeping older eyes healthy. For example, a study of healthy volunteers found that tears and eyelid bacteria became “more inflammatory” with age – older people had higher levels of inflammatory molecules (like ICAM-1 and IL-8) on the conjunctiva after age 60 (). Over the years older eyes often make fewer and thinner tears () and blink less, which may let more irritants and microbes accumulate. At the same time, enzymes and toxins from certain eyelid bacteria (e.g. Staphylococcus aureus) can stimulate inflammation and damage the tear film () (). In a combined effect, an aged ocular surface can become chronically irritated. Recent studies confirm that the mix of microbes on the eye changes with age. Using DNA sequencing, scientists showed that “young” and “old” adult eyes have different bacterial communities and gene functions (). In other words, growing older appears to reshape which bacteria thrive on the eye. These shifts seem to favor some types of microbes that can make inflammation worse. (Older patients often also use eye drops for conditions like glaucoma; those drops – especially if they contain preservatives – further alter the ocular flora ().) In short, aging eyes often show microbial changes that go along with a tired tear film and low-grade eyelid inflammation. Age-Related Microbiome Changes and Ocular Surface Inflammation Dry Eye and Meibomian Gland Dysfunction (MGD) Dry eye disease (DED) is very common in older adults. It happens when the tears can no longer keep the eye surface wet and nourished. DED has two major forms: one where the tear glands make too little water, and another where tears evaporate too quickly (often because of poor oil quality). The oil layer of tears comes from the meibomian glands in the eyelids. As people age, these glands more often become blocked or change their normal oil composition. This meibomian gland dysfunction (MGD) leads to very oily tears or no oil at all, making eyes dry and inflamed. In fact, about 70% of dry eye patients have MGD (). Recent research has found that the bacteria living in and around the meibomian glands are different in MGD. Shotgun DNA sequencing of meibum (the gland oil) showed that people with MGD have a “distinct microbiota” in their eyelid secretions (). For example, potentially harmful bacteria like Campylobacter coli, Campylobacter jejuni, and Enterococcus faecium were abundant in MGD glands but nearly absent in healthy controls (). These bacteria carry genes for strong virulence factors (such as immu