Dry Eyes... Simple Problem, Complex Solution

Although ENT doctors are not eye specialists, dry eyes are a very common complaint we often hear. Although the problem sounds very simple, the treatment often is not as straightforward as you might think. In order to understand why dry occurs occur, as well as what treatments may help, normal tear creation must first be understood.

Keep in mind that ENT doctors will typically check for Sjogren's Syndrome especially if there is concurrent dry mouth complaints. Lubricating eye drops are recommended to provide symptommatic relief until a more comprehensive evaluation can be performed by an eye care specialist. 

Moving on... Tears are actually quite complex composed of 3 different layers secreted by different glands and tissues. There is the oily outermost lipid layer. The water-like middle aqueous layer. And finally the innermost mucin layer. The lacrimal gland located above the eye produces the aqueous layer by continuously releasing fluid that coats the eye’s surface. It is what most people would consider the eye’s natural moisture.

An eye specialist may perform some or all of the following tests to evaluate each of the 3 tear film layers:

• Schirmer Test - aqueous 

• Phenol Red Thread Test - aqueous 

• Epithelial Staining (rose bengal, lissamine green, fluorescein) - mucin layer 

• InflammaDry - all 3 

• Lactoferrin - aqueous 

• TearLab (Tear Osmolarity) - aqueous 

• Meibomian Gland Evaluator - lipid 

• LipiView - lipid

The oily lipid layer is produced by the meibomian glands located within the eyelids. The lipid layer protects the eye’s moistness or aqueous layer and allows the eyelid to glide safely over the eye. The cells on the inner wall of the meibomian gland produce the oil in a normal eye. When you blink, the eyelids touch and pressure is applied to the meibomian glands causing them to eject small amounts of this oil into the tears. The upper eyelid then pulls the oil upward over the eye. As the lid opens fully, the oil disperses evenly over the entire eye surface. The oil stabilizes the tear film evenly as well as prevents the aqueous layer from evaporating rapidly. The oil also increases lubrication and comfort. When there is not enough oil present, the aqueous layer may evaporate quickly leading to dry irritated eyes. Inadequate oil production may occur due to Meibomian gland blockage or simply from not blinking often enough as the blink is what causes the oil to discharge over the eye.

The mucin layer is the deepest layer of the tear film and adheres firmly to the eye’s surface. The mucus found in the mucin layer is produced by conjunctival epithelial cells as well as within the crypts of Henle and glands of Manz. This mucus layer allows the aqueous layer to adhere to the eye’s surface, thereby preventing beading. By lowering the surface tension between the aqueous and mucin layers, it also acts as a wetting agent and a stabilizing agent for the tear film between blinks. 

The main initial goto treatment for dry eyes are artificial tear drops which attempt to restore a normal tear film. When artificial tear drops are purchased to help with dry eyes… keep in mind that different brands use different mixes of ingredients to address deficiencies in one or more layers of the tear film. For example, if dry eyes are mainly due to an inadequate lipid layer causing rapid evaporation of the aqueous layer, an eye drop containing more oil based ingredients would work better than an eye drop that provides a more aqueous hydration.

For dry eyes due to inadequate oil production, or some type of meibomian gland dysfunction, that does not respond to over-the-counter eye drops, more aggressive medical treatments geared towards unblocking and/or stimulating the meibomian glands will be required.

As an aside... Eye drops which are NOT recommended to treat dry eyes (may actually make dry eyes worse!) include Clear Eyes, Visine, and Naphcon-A.