What is the most common cause of Evaporative Dry Eye?

• A. Sjogren's syndrome
• B. Nocturnal lagophthalmos
• C. Parkinson's disease
• D. Meibomian gland dysfunction (MGD)

Answer: (D)

Evaporative dry eye happens mainly when the tear film loses its protective oily layer. That oily layer comes from the meibomian glands along the eyelids. When these glands are blocked, inflamed, or produce poor-quality lipid (meibum), the lipid layer becomes thin or unstable. Without a healthy lipid layer, tears evaporate too quickly, leaving the surface dry and hyperosmolar. That makes Meibomian gland dysfunction the most common cause of evaporative dry eye.

Other conditions, like Sjögren's syndrome, primarily reduce the aqueous tear quantity by attacking the lacrimal glands, leading to aqueous-deficient dry eye rather than evaporative. Night-time eyelid reopening (lagophthalmos) or neurological issues can contribute, but they are not the leading cause of evaporative loss. In many patients there is some overlap, but MGD is the main driver of evaporative dry eye.