What type of dry eye do you have?
One of the first things we like to check is your tear volume. We do this first as we don’t want to have touched your eyes or put any drops in at all. In other words, we want to know what the usual amount of tears in your eyes is. The assessment involves putting a bit of paper (Schirmer test) or string (Phenyl Red Thread test) and, after a specified amount of time, measuring how much of the paper/string has been wet with your tears.
The amount of tear volume in your eye is an essential measure as it differentiates between the 2 major groups of dry eye:
1. Aqueous deficient dry eye (ADDE) where there are insufficient watery tears, and
2. Evaporative dry eye (EDE, also know as meibomian gland dysfunction/disease ) where there is insufficient oil in the tears.
Most practitioners would now agree that most people with dry eye have a combination of the two. Having said that it is still a very important differentiation as it affects the treatment options that we use.
Meibomian gland assessment
The next step is to assess the meibomian glands. There are about 30 of these glands along the lid margins and they produce the oily film that coats the surface of the watery, aqueous tear layer. It prevents evaporation of the tears and makes the lids feel more comfortable when blinking. We examine the glands by everting the lid and usually photograph how they look. We can then tell if the glands have shrunk or even dropped out all together. We then press the glands to see what the quality of the secretions is like and what sort of volume comes out under pressure. Ideally, the glands produce a beautiful droplet of clear oil but this can look quite buttery and even like toothpaste. Where the glands are producing these thickened secretions and/or there is inflammation or blockage of the glands we refer to it as Meibomian Gland Dysfunction (MGD/Meibomian Gland Disease/Meibomianitis/Posterior Blepharitis). This is the cause of Evaporative Dry Eye.
Examining the front surface of your eye