Why Dry Eye Affects Contact Lens Wearers
Contact lens-related dry eye is the leading cause of lens discomfort and one of the primary reasons patients reduce wearing time or abandon contact lenses altogether. The presence of a contact lens fundamentally alters tear film dynamics, creating conditions that promote dryness even in patients who have adequate tear production without lenses.
Understanding the mechanisms behind contact lens dryness allows practitioners to select appropriate materials, modify wearing habits, and implement targeted treatments that keep patients comfortable and compliant.
Mechanisms of Dryness
Lens Dehydration
Soft contact lenses are hydrogel or silicone hydrogel polymers that contain a specific percentage of water. During wear, the lens gradually loses water to evaporation from its anterior surface. As the lens dehydrates, it draws replacement moisture from the tear film beneath it:
- This creates a cycle where the lens dehydrates the pre-lens tear film, causing symptoms
- Environmental factors accelerate dehydration: low humidity, air conditioning, heating systems, airplane cabins, and windy conditions
- Dehydration worsens as the day progresses, explaining the classic "end of day discomfort" pattern
Reduced Blink Rate
Studies show that the blink rate decreases significantly during concentrated visual tasks:
- Normal blink rate: approximately 15-20 blinks per minute
- During computer use or reading: may drop to 5-7 blinks per minute
- Fewer blinks mean less tear film renewal across the lens surface
- Incomplete blinks (where the upper lid does not fully close) compound the problem by leaving the inferior lens surface exposed
Tear Film Disruption
A contact lens physically splits the tear film into a pre-lens tear film (in front of the lens) and a post-lens tear film (between the lens and cornea). The pre-lens tear film is thinner than the normal tear film and breaks up more rapidly, reducing the interval between blinks when the cornea and lens surface are adequately lubricated.
The Water Content Paradox
Counterintuitively, higher water content lenses can worsen dry eye symptoms:
- High-water lenses (>50% water content) lose water faster through evaporation due to the larger water reservoir available for evaporation
- As they dehydrate, they draw more aggressively from the tear film to maintain their equilibrium water content
- Lower-water-content lenses (<40%) dehydrate less and draw less moisture from the tears
- Silicone hydrogel lenses generally maintain hydration better than conventional hydrogels of equivalent water content
Management Strategies
Lens Selection
- Lower water content materials: Less susceptible to dehydration
- Silicone hydrogel lenses: Better resistance to dehydration than conventional hydrogels
- Daily disposable lenses: A fresh lens every day avoids the accumulation of deposits that increase surface wettability problems
- Lenses with surface treatments: Some manufacturers incorporate wetting agents or plasma surface treatments to improve tear film stability
Rewetting Drops
- Preservative-free rewetting drops formulated for contact lens use provide temporary relief
- Instruct patients to apply drops before symptoms develop, not after discomfort is already established
- Some drops are designed to be applied over the lens; others should only be used before insertion or after removal
Environmental Modifications
- Use humidifiers in air-conditioned or heated environments
- Position computer screens below eye level to reduce palpebral aperture width
- Take regular breaks during extended screen time (the 20-20-20 rule: every 20 minutes, look at something 20 feet away for 20 seconds)
Blink Training
- Conscious blink exercises help patients restore normal blink rate and completeness
- Particularly important for computer users and students
Key Takeaways
- Contact lens-related dry eye results from lens dehydration, reduced blink rate, and tear film disruption
- Higher water content lenses can paradoxically worsen dry eye by dehydrating faster
- The pre-lens tear film is thinner and less stable than the normal tear film
- Management includes lens material selection (lower water, silicone hydrogel, daily disposable), rewetting drops, environmental modifications, and blink training
- End of day discomfort is the classic presentation as lens dehydration accumulates throughout the day