Optometrists have known for a long time that Dry Eye Disease damages the cornea, which is the front curved part of the eye that is responsible for a significant portion of the eye's
optical power. In a recent study, published in the December 2014 volume of Optometry and Vision Science, researchers found that Dry Eye Disease actually decreased the thickness of the corneal epithelium. In effect, dry eyes may have a thinning effect on certain areas of the cornea.
The human cornea is made up of several layers, most notably are the epithelium (outer layer), stroma (middle layer),and endothelium (inner layer). It's the epithelium that requires a consistent coat of moisture; the epithelium is also the resting place for contact lenses. Investigators measured corneal epithelial thickness in patients of varying degrees of dry eye severity.
What they found is that the superior (near 12 o'clock) portion of the cornea was thinnest in patients with the most severe dry eyes. This is perhaps one of the first studies that showed this correlation. One possible explanation for these findings is that as the surface of the eye becomes dry, there is less moisture to lubricate the friction created by the blinking of the upper eyelid across the surface of the eye. With more friction, the superior eyelid blinking may slowly be breaking down or eroding the thickness of the corneal epithelium.
But, what are the symptoms created as the dry eye damages the cornea? One of the biggest symptoms may be discomfort. Disruptions to any part of the cornea may result in irritation and sandy or foreign-body type sensations. The other symptom is instability of vision. If the surface on which the tear film is spread across becomes uneven, the moisture layer becomes unstable. And an unstable moisture layer produces unstable or fluctuating vision. Yet, another potential symptom may be uncomfortable contact lens wear.
This study, while providing new insight, points back to common clinic observations: dry eyes produce changes to the integrity of the cornea which in turn can affect vision and ocular comfort. Treating dry eyes, through various prescription and non-prescription means, can help improve these findings and provide and a tangible benefit to patients suffering from dry eyes.