Balancing the Ocular Microbiome

The microbiome plays a key role in the health of the ocular surface, protecting against pathogenic bacteria and modulating immune response—a delicate balance that is essential for preventing infection and the onset of diseases such as dry eye disease (DED).

“When we consider the ocular microbiome, we are referring mostly to the ocular surface low-biomass microbiome, the diverse and dynamic community of microorganisms that are present mainly in the deeper folds of the conjunctiva, as well as in the lower and upper lids, and partially on the cornea,” Heleen Delbeke MD, PhD said in an interview.

A healthy ocular surface microbiota, maintained through immune tolerance, provides the eye with protection from invading pathogenic microbes. By contrast, an imbalance to this system, known as dysbiosis, can lead to an increased risk of ocular disease.

Dr Delbeke noted that a range of factors can disrupt the normal balance between the protective and harmless microorganisms, allowing more harmful bacteria to proliferate. The loss of surface homeostasis promotes inflammation, increasing susceptibility to other diseases.

For instance, patients wearing contact lenses experience a well-known change in their ocular surface microbiome, which comes to more closely resemble that of the skin. This might increase the risk of meibomian gland disease, DED, infectious keratitis, and, reportedly, keratoconus, Dr Delbeke pointed out. Regarding keratoconus, she cautioned against drawing conclusions, citing the multifactorial nature of corneal ectasias and the tendency of keratoconus patients to rub their eyes more frequently. This raises the possibility that changes in the ocular microbiome may be an effect of the disease rather than the cause.

There are also many factors that can trigger dysbiosis of the ocular surface. Endogenous factors such as age, genetics, biological sex, and hormonal status are all likely dysbiosis triggers, while exogenous triggers include geographical location, nutrition, and air pollution.

She noted that there are ocular biodome differences between patients living in urban and rural areas, those following a healthy diet versus one high in sugar and fat intake, and even those who frequently use swimming pools. There is even a seasonal difference in ocular microbiome composition between winter and summer.

According to Dr Delbeke, there is interest in further investigating the mechanisms behind ocular dysbiosis as a means of preventing and treating many ocular diseases.

“There has been a little bit of research done on the potential of prebiotic and probiotic foods and supplements, as well as faecal transplants, to reduce symptoms of dry eye disease,” she said. “I think that once we have a clear and precise idea of what a normal ocular microbiome looks like, what the normal variation is, and what a really diseased state looks like, we would be able to intervene.”

Heleen Delbeke MD, PhD is a cornea, cataract, and refractive surgeon at University Hospitals Leuven, Belgium. heleen.delbeke@uzleuven.be