Mucous

[kimby2007]

Hi Dr. Holly:

Thanks for taking the time to answer our questions. I was hoping to get your opinion on mucous strings. I was once told mucous strings are part of an allergic reaction and then once that it was because of a mucin problem. I have allergies and Sjogrens. In my unscientific opinion I believe the mucous strings are related to the dryness not the allergies, but I would be glad to get your opinion on the matter.

Kim

[Frank Holly PhD]

Hi Dr. Holly:

Thanks for taking the time to answer our questions. I was hoping to get your opinion on mucous strings. I was once told mucous strings are part of an allergic reaction and then once that it was because of a mucin problem. I have allergies and Sjogrens. In my unscientific opinion I believe the mucous strings are related to the dryness not the allergies, but I would be glad to get your opinion on the matter.

Kim

Hi, Kim; I have to be short. This is an area of ocular surface phenomena where interface chemistry truly shines. Again the research started in Denmark and somehow the ball ended up in my corner.

Mucin - a rod-like macromolecule - iis highly water soluble and yet has high surface activity. It also interacts with lipids and stabilizes the superficial lipid layer. One role we have not mentioned is functional at the tear layer - cornea interface. The mucous layer at this location does not only lessens the interfacial tension but also masks the lipid molecules when they arrive at that location. The mucous layer can contain up to 35-40% lipid and still remain hydrophilic.

When it contains more than the upper limit the mucus layer will become unstable in a sheet form due to increased tension. Under the shear forces created by lid motion, the sheets roll up (strudel-like) and form fibrils and strings. These are pushed down to the lower cul-de-sac and collect at the canthus or pass through the puncta. A self-cleaning proess affecting the mucus layer.

The direct cause may be an excess polar fraction of lipids or several other subtle processes that increases the lipid-mucin ratio.

When permanent dry spots exist on the ocular surface, these strings are attached to the dry spots by hydrophobic bonding. Lid motion will yank at these locations and can erode surface cells - a painful process causing inflammation, e.g. filamentary keratitis.

Eye drops used to exist to break up these filaments and assist in their removal.