What is dry eyes?
Dry eye is a medical condition in which the eyes do not produce enough tears. You may wonder why that is a problem. The human eye needs to produce a certain amount of tears to remain healthy and comfortable so if the eye does not produce enough tears, it is a problem. A common type of dry eye disease is when the eye does not produce the right type of tears and tear film.
Understanding the importance of tears
Each time you blink, a film of tears spreads over your eyes to keep their surface clear and smooth. In other words, your tear film promotes clear vision. There are three layers of tear film and they are the mucus layer, watery layer, and oily layer.
The oily layer is outside the tear film and its purpose is to make the eyes’ surface smooth. It also prevents the tears from drying up too quickly. The oily layer is produced in the Meibomian glands. The watery layer is the middle of the tear film and it makes up most part of the visible tears. Its major function is to clean the eyes by washing away dirt or particles from the eyes. This layer comes from the Lacrimal glands right in the eyelids.
The mucus layer is the inner layer of the film and it ensures that the surface of the eyes is always moist by spreading the water layer over the eyes’ surface. This layer comes from Conjunctiva. Sometimes the eyes do not produce enough tears or one or more of the three layers become dysfunctional. Either case will lead to what is known as dry eyes. Dry eye can be diagnosed through three major tests that have been outlined below.
Common dry eye tests used during a dry eye assessment
This test can be carried out using various osmolarity instruments. The osmolarity test assesses the quality of tears with results displayed in most/l. An elevated reading, >300 mOsm/L, indicates loss of tear film homeostasis. When the inter-eye difference is >8 mOsm/L, it indicates instability of the tear film. The iPen and Tearlab are two common examples.
To perform this test, a patient is first given numbing drops to reduce the discomfort that the test may cause. The optometrist will then pull down the lower eyelid and place a strip of paper beneath it. After that, the patient will close their eyes and leave it closed for 5 minutes. The strip is removed thereafter and the amount of moisture in it is measured. Dry eye disease is diagnosed if the amount of moisture is insufficient.
Red Thread Test
This is a very similar version of the Schirmer’s test. The main difference is that the strip is replaced with a red thread in this test.
Oculus Keratograph 5M
This is an advanced form of corneal topography coupled with specific dry eye tools. It consists of a keratometer, topographer and a color camera that has been optimized for external imaging. Apart from topography and external imaging, the equipment helps to evaluate the lipid layer, measure the tear meniscus height and performs a non-invasive tear film break-up time. Optometrists use this tool to diagnose the specific type(s) of dry eye disease involved. It also helps provide comparative pre and post treatment analysis.
This is an imaging study of the morphology of meibomian glands in vivo. The test is for the purpose of examine the upper and lower meibomian glands and to assist in diagnosing Meibomian gland dysfunction (MGD).
Patients with dry eye syndrome are advised to see an optometrist with the right equipment to run a comprehensive diagnostic battery of tests. Specific tests tailored for the diagnosis of dry eyes will help narrow the diagnosis and the root cause of the condition and ultimately helps in providing a guide for a targeted treatment.