Understanding Dry Eyes
Dry eyes occur when your tear glands don’t produce enough tears to lubricate your eyes. This condition can be uncomfortable and painful. It can be caused by both medical and environmental factors.
The eyes produce tears all the time. When you blink, yawn or laugh, a film of tears spreads over the eye. This keeps the eye’s surface smooth and clear. The tear film is important for good vision and prevents the eyes from becoming dry and enables clear vision.
Tear Film Can Become Unstable
When you blink, a film of tears spreads over the eye. This keeps the eye’s surface smooth and clear. The tear film is important for good vision.
The tear film is made of three layers:
- An oily (lipid) layer
- A watery (Aqueous) layer
- A mucus (mucin) layer
- you don't produce enough watery layer of tear film (~ 20%) – Aqueous deficient dry eye
- tears evaporate too fast due to damage in lipid layer of the tear film (~80%) - Evaporative dry eye
- Mix of both
The Scientific Explanation
How Dry Eyes Happen
The lipid layer of our tear film act as a seal for the watery aqueous layer preventing it from evaporating (see Fig 1).
However, in 80% of people who suffer from dry eye, the cause of their dry eye is due to deficiency or instability of the lipid layer of the tear film resulting in tears evaporating too fast causing dry, irritated eyes (See Fig 2)
Figure 1: The tear film
Three main layers make up the normal tear film. In 80% of people with dry eye, the cause is deficiency or instability of the lipid layer causing tears to evaporate too fast.
Most eye lubricant only replenishes the water layer of the tear film and needs to be re-applied frequently because they do not seal in moisture.
Fig 2. Healthy tear film (left) Unstable tear film (right) due to damaged lipid layer can cause increase evaporation of tears causing dry and irritated eyes.
Source: https://www.nzoptics.co.nz/
