Mucins play an integral role in ocular surface health. They are the secret ingredient that gives the aqueous its viscosity and moisturizing properties. They entrap pathogens in the tear film to protect the eye. And they provide the glycocalyx anchor that keeps the tear film residing on the ocular surface. In this episode, Anna Tichenor, OD, PhD, of Indiana University explains all this and more in the no-nonsense terms you’d expect from a Midwesterner.

There are two types of mucin: free-floating and membrane-bound. The former are secreted by conjunctival goblet cells into the tear film, where they scavenge for bacteria and pollen while also providing the hydration properties of the tears. Membrane mucins, by contrast, arise from corneal and conjunctival epithelial cells and produce the glycocalyx, “kind of a shag carpet” on the ocular surface. Dr. Tichenor explains. Functionally, this creates a hydrophilic base that adheres the tear film to the eye.

The discussion then delve into clinical manifestations of these mucin properties, beginning with lissamine staining and what it signifies—dead or devitalized corneal epithelial cells that also have patches of missing glycocalyx.“Those areas are not going to be wetting very well,” Dr. Tichenor explains, “and would be very prone to infection.”

The team also offers advice on how to identify the Line of Marx at the mucocutaneous junction on lissamine green staining and what it might signify, as well as the role of mucins in lid wiper epitheliopathy.

Although fluorescein patterns are most often interpreted in the context of lipid layer integrity, Dr. Tichenor offers a nice clinical pearl on what they may say about the state of the glycocalyx, too: watch for the fluorescein spreading pattern across the cornea. If you see dark patches form almost immediately after a blink, “I would interpret that as areas where the glycocalyx is not functioning as well as it could.”

Membrane mucins are an effective early warning system. Inflammation is widely recognized as the key driver of dry eye, and research points to mucin as a potential regulator of inflammatory cytokines, Dr. Tichenor explains. Furthermore, overproduction of mucus happens in response to an antigen on the ocular surface—a threat that needs to be eliminated. This might be a clue to mucin deficiency in, for instance, Sjögren’s Syndrome.

This episode emphasizes that mucins contribute to dry eye cases in important ways that shouldn't be overlooked in favor of lipid-based mechanisms and interventions. Other mucin-mediated conditions include ocular cicatricial pemphigoid, mucus fishing syndrome, filamentary keratitis and Stevens-Johnsons Syndrome.

Despite the paucity of mucin-specific treatments available in the US. Dr. Tichenor explains that some artificial tears have “mucomimetic” properties, especially those containing hyaluronic acid. The potential of topical vitamin A is also touched on, as well as two drugs available internationally: diquafosol and rebamipide.

“Have mucins on your mind” as you assess dry eye and other ocular surface conditions, is Dr. Tichenor’s takeaway for the episode.

Relevant articles:

A Sticky Subject

As Smooth As Silk

Dry Eye Drop Boosts Ocular Mucins

Regional Conjunctival Differences in Glycocalyx Mucin Expression in Dry Eye and Normal Subjects