Abstract
Purpose :
The typical chemical structure of mucins which are involved in tear liquids as a main constituent implies the surface activation property while its evidence has never been confirmed. If they act as surfactants, the tear liquids effectively spread over ocular surfaces forming a very thin and stable tear film without dry islands. In other words, the wettability of mucin solution seems magnified by the existence of mucin molecules. As a result, the lubrication between the ocular surface and the eyelid, and probably that between the surface and a contact lens, are controlled by the concentration of mucin. In order to justify this newly suggested molecular mechanism of dry eye, we measured the surface tension of mucin and hyaluronan (HA) solutions both of which are solutions of polyanions.
Methods :
A mucin extracted from mesoglea of jellyfish (qniumucin: Q-mucin) was used as a standard mucin. The surface tension of each solution was measured in a pendant drop method which can be applied to a single droplet. Droplet shapes were monitored by a TV camera and automatically analyzed by a laptop computer using Young-Laplace equation.
Results :
The surface tension of Q-mucin solutions (0.1-10mg/mL) dissolved in saline and pure water was measured. On increase of Q-mucin concentrations in pure water, the surface tension values were gradually decrease from 72 mN/m (that of water) down to 60 mN/m for (10 mg/mL). The lineshapes were similar to that known as a typical behavior of surfactants. In saline solutions of Q-mucin, essentially the same lineshapes were obtained. Contrastingly, saline solutions of HA showed almost no change in surface tension on increase of HA concentration. These results indicate that the mucin solutions have surface activation property but HA solutions do not.
Conclusions :
Wettability and lubricating property of tear films seem to be sustained by mucin molecules in tear liquids. Only mucin has this ability because it can effectively act as a surfactant. While it is used as an additive to eye drops, HA did not show any surface activation properties.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.