What is Dry Eye?
Dry Eye Disease (DED) is a multifactorial ocular surface disease characterized by loss of tear film homeostasis and associated ocular symptoms.
According to the Dry Eye Workshop II -2017 (DEWS II) report [1] “Dry eye is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, and accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiological roles."
Key pathophysiological drivers [2-4]
Tear film instability:
Disruption in tear film structure or function, causing rapid breakup and exposure of the ocular surface.
Hyperosmolarity:
Elevated tear osmolarity damages ocular surface cells and triggers inflammation.
Ocular surface inflammation:
Chronic ocular surface inflammation perpetuates tissue damage and symptoms.
Neurosensory abnormalities:
Altered corneal nerve function contributes to symptom severity and disease chronicity.
DED is not a single-point failure - it's a self-perpetuating cycle [2, 5]
Tear film instability and hyperosmolarity initiate inflammatory cascades.
Ocular surface inflammation worsens tear film instability.
Neurosensory abnormalities amplify symptoms and perpetuate the cycle [6, 7].
This vicious cycle explains why DED requires a multifactorial diagnostic and therapeutic approach rather than a single intervention.
Classification of dry eye:
Dry eye disease is commonly divided into two major subtypes, which may occur independently or in combination:
a.Aqueous-Deficient Dry Eye (ADDE)[8]
- Characterised by reduced tear production from the lacrimal glands, resulting in insufficient aqueous volume.
- Etiologies include age-related lacrimal gland hypofunction, autoimmune diseases such as Sjögren's syndrome, and medication-induced hyposecretion.
- Reduced tear volume compromises tear film stability and increases exposure of the ocular surface, leading to ocular discomfort, foreign body sensation, and visual disturbance.
b.Evaporative Dry Eye (EDE)[9]
- Results from excessive evaporation of the tear film, most commonly due to meibomian gland dysfunction (MGD).
- Abnormal or insufficient lipid secretion reduces the stability of the lipid layer, accelerating evaporation of the aqueous component.
- Clinically, this can manifest as reflex tearing, fluctuating vision, and ocular surface irritation, despite apparently normal or increased tear volume.
- Note: Many patients present with mixed DED, where both aqueous deficiency and increased evaporation contribute to disease pathophysiology. Recognising the predominant mechanism is essential for targeted therapy.