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Describe dry eye disease with its classification, investigation and management.

Ophthalmology · 3rd Professional

Nature and Classification

Dry eye disease is a multifactorial disease of the ocular surface characterised by loss of homeostasis of the tear film, with tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormality.

Two concepts IN that definition drive modern treatment: hyperosmolarity, which is the core mechanism damaging the epithelium and triggering inflammation; and inflammation, which is why anti-inflammatory treatment works and why lubricants alone often do not
The vicious circle — reduced or unstable tears raise osmolarity; hyperosmolarity damages epithelial and goblet cells and releases inflammatory mediators; inflammation further damages the glands and the goblet cells and damages the corneal nerves; and the resulting reduction in reflex secretion perpetuates the cycle. Breaking the circle, not merely wetting the eye, is the aim

Category	Causes
Aqueous-deficient — sjogren	Primary Sjogren syndrome (dry eye, dry mouth and autoantibodies) and secondary Sjogren with rheumatoid arthritis, systemic lupus erythematosus or systemic sclerosis. Anti-Ro (SS-A) and anti-La (SS-B) antibodies; lymphocytic infiltration of the lacrimal and salivary glands, with a raised lifetime risk of lymphoma
Aqueous-deficient — non-sjogren	Age-related lacrimal gland atrophy.
Evaporative — lid-related	Meibomian gland dysfunction and blepharitis (the leading cause); lid aperture disorders — proptosis, lagophthalmos, ectropion; and a low blink rate with screen work, reading and in Parkinson disease
Evaporative — surface-related	Vitamin A deficiency, which causes mucin deficiency through goblet cell loss; topical drugs and preservatives; contact lens wear; and allergic eye disease
Iatrogenic and environmental	Systemic drugs — antihistamines, anticholinergics, beta-blockers, diuretics, isotretinoin, antidepressants and hormone therapy; refractive surgery.

Symptoms, Signs and Investigation

Symptoms — grittiness, burning, foreign-body sensation, itching, photophobia, fluctuating blurred vision that clears on blinking, contact lens intolerance, and — paradoxically — watering from reflex hypersecretion
A characteristic feature is that symptoms exceed signs, particularly early; and in severe long-standing disease with corneal nerve damage the reverse may be true, with marked signs and few symptoms
Symptoms are worse with reading, screen work, driving, air conditioning, wind and in the evening.

Test	Method and interpretation
Tear break-UP time (TBUT)	Fluorescein is instilled and the time to the first dry spot measured after a blink. Less than 10 seconds is abnormal, and a short TBUT with a normal Schirmer indicates evaporative disease. It is the simplest and most useful test
Schirmer I test	A 5 × 35 mm filter strip in the lower fornix for 5 minutes, without anaesthetic, measuring total (basal plus reflex) secretion. Less than 10 mm is abnormal and less than 5 mm is severe. Performed with anaesthetic it measures basal secretion. It is poorly reproducible and normal in evaporative and mucin-deficient dry eye — which is its principal limitation
Fluorescein staining	Stains areas of epithelial loss on the cornea; graded by the Oxford or NEI scheme
Lissamine green or rose bengal	Stain devitalised and unprotected cells, and are better for the conjunctiva. Rose bengal stings considerably; lissamine green is equally informative and comfortable, and has replaced it
Tear osmolarity	Raised above 308 mOsm/L; a direct measure of the core mechanism and useful for monitoring
Meibography and interferometry	Image gland dropout and the lipid layer thickness
Matrix metalloproteinase-9	A point-of-care marker of ocular surface inflammation
Systemic tests	Anti-Ro and anti-La, rheumatoid factor, ANA, ESR; salivary gland biopsy where Sjogren is suspected

Management

Treatment is a ladder, and severity determines the rung:
Step 1 — education and environment: explain that the condition is chronic and controllable rather than curable; take breaks from screen work and blink deliberately (the blink rate falls by more than half at a screen); lower the screen below eye level to reduce the exposed surface area; humidify; avoid direct air conditioning and fans; and review systemic drugs with the physician
Step 1 — lid hygiene with warm compresses and massage for meibomian dysfunction.
Step 1 — tear substitutes: drops by day, gels and ointment at night. Preservative-free preparations are essential above about four instillations daily.

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