Meibomian Glands Evaluation
Current research suggests that 85% of patients struggling with dry eye have a meibomian gland dysfunction. In a normal, healthy eye, the meibomian glands produce meibum, a substance similar to the color and consistency of generic vegetable oil. With each blink, a small amount of this oil is expressed from the meibomian glands and onto the ocular surface. The upper eyelid then pulls that oil over the surface of the eye. The purpose of this oil is to prevent evaporation of the tears, to create a smooth ocular surface resulting in clear consistent vision, and to decrease friction between the ocular surface and the upper eyelid.
In Meibomian Gland Dysfunction (MGD), the oil is thick -almost like toothpaste- and can clog the glands. This results in little to no oil being expressed upon blinking. The tears on the eye evaporate quickly, causing a gritty, dry sensation, and difficulty staying comfortable in contact lenses. As part of the meibomian gland evaluation, it is necessary to evaluate the type of oil that is expressed.
Clean, shiny lid margin on a healthy eye
Grade 1: milky, cloudy “turbid” secretion
Grade 2: Milky, boarderline pasty. Capped glands, more difficult to express but may “pop” like a pimple.
Grade 3: Thick toothpaste-like oil that can be very difficult and painful to express
Grade 4: No expression and “notching” of the lid margin, indicating significant gland atrophy
Chronic blockage results in atrophy, or degeneration, of the glands. Unfortunately, gland atrophy is permanent damage. Once you lose the glands, you cannot get them back, so it’s vital to catch MGD before the damage/atrophy becomes too progressive.
Gland Evaluation and Degrees of Atrophy
The picture in the middle of the chart below is a great place to start the discussion of atrophy. The top picture (Degree 0 loss) is a healthy eye. The long yellow lines are the glands and the orange is the space between the glands. All the glands extend from the base of the lid to the lid margin. As you move down the scale (jump to Degree 4), you can see that the yellow lines are just stubs in comparison to Degree 0). Patients at grade 4 atrophy tend to be very uncomfortable, with chronic red, and irritated painful eyes. The pictures in the left hand column are the infrared photos of the real anatomy in dry eye patients. The sooner we discover the problem here, the more proactive we can be at slowing down this process.
Staining of the conjunctiva with dyes like Lissamine Green and Rose Bengal allows us to visualize dead and devitalized cells on the ocular surface. Any cells that are either dead or dying will absorb the dye. The amount of staining we see is then used to grade the degree of ocular disease.
Mild conjunctival staining
Moderate conjunctival staining
Lid Wiper Epitheliopathy
Lid Wiper Epitheliopathy can be evaluated using the same Lissamine Green dye seen above. Lid Wiper Epitheliopathy is a condition that occurs due to ocular trauma and friction between the upper lid and the ocular surface. This staining can present in a number of ways:
- Feather-like pattern: Stains that start vertically from the edge of the lid in narrow brushstroke shape and variable length.
- Band pattern: This most common type of stain adopts a uniform band shape from the nasal to the temporal side of the inner eyelid margin. It often thickens at the center and then slightly thins towards the edges.
- Irregular pattern: Stains without any defined shape
The aqueous, or water portion of the tears, is found between the mucin layer on the surface of the eye and the lipid layer, provided by the meibum from the meibomian glands. Aqueous is produced by the lacrimal gland up by the temple on the head, and drains through the punctum (inner tearduct). Research suggests that only a small percent of people have aqueous deficiency alone without a evaporative component (MGD). Since it can occur, however, we regularly monitor for it.
Osmolarity refers to the concentration of salt in the tears. One way to think of this is like brewing coffee. If you use just a little bit of coffee grounds, but pour a bunch of water of them, the resulting brew is pretty weak. If you take a few heaping spoonfuls of coffee and pour just a small amount of water, that’s going to be a strong brew! The water and salt on your eye is similar. If you don’t have much water (aqueous) on your ocular surface, your tears will be quite salty, or have high osmolarity. If you have plenty of water on your eye, the concentration of the salt will be lower, and you will have low osmolarity. Normal osmolarity should be below 300 milli-osmols per liter of tears.
At Valley Eye Clinic, we use TearLab - a simple, painless way to monitor your tear osmolarity. This test can be repeated over time to give a quantitative analysis of your changing ocular surface osmolarity levels to help determine and maintain the best course of treatment.