Epidemiology^[2]

Dry eyes is a common condition affecting up to a third of those aged over 65 years. It is 50% more common in women than in men.

Aetiology^[1][2][3]

Dry eyes can arise as a result of insufficient tear production, excess tear loss, abnormalities of eyelids and blinking, or changes in tear film composition. Different forms of dry eye interact with each other, creating a vicious circle. Inflammation is both a cause and a consequence of dry eye, and can have a key role in maintaining the vicious circle. The inflammation does not necessarily manifest as redness. Preservatives found in artificial tears (particularly benzalkonium chloride) also contribute to the problem.

Common causes^[2]

Most people with dry eyes have no measurable abnormality of tear production, and no serious disease affecting tear composition. Common causes are:

• Decreased tear production, commonly due to:
  • Blepharitis, eg from seborrhoeic dermatitis, atopic dermatitis, or rosacea.
  • Adverse effect of drugs (see box).
  • Allergic conjunctivitis.
• Increased evaporation of tears due to:
  • Low humidity - from central heating, air conditioning or high wind conditions.
  • Low blink rate, wide lid aperture, eg from prolonged use of a computer or microscope.
  • Allergic conjunctivitis.

Other causes

Contributing factors

Risk factors for dry eye include:

• Diet low in omega-3 essential fatty acids (or low omega-3 to omega-6 ratio).
• Decreased androgens (pregnancy, oral contraceptive pill, hormone replacement therapy).
• Low-humidity environments, computer use or prolonged reading, smoking, vehicle pollution.
• Refractive surgery and use of contact lenses.
• Malignant tumours (due to radiotherapy and systemic chemotherapy).

Presentation^[2][3]

Symptoms

The diagnosis is usually made on the history:

• Gritty irritation and foreign body sensation.
• Burning or mild pain, aggravated by air conditioning, prolonged reading or computer work, dry air, etc.

Symptoms tend to be worse towards the end of the day. Less often, there may be itching, photophobia and a tired or heavy feeling. Some patients may report a lack of emotional tears or may have noticed a less vigorous response when peeling onions. Some patients paradoxically complain of too much tearing - an excessive reflex response to corneal dryness.^[3]

Signs

• May have mucous discharge and strands of mucin on the corneal surface.
• Corneal signs - may have signs of keratopathy, eg punctate epithelial erosions, filament and plaque depositions on the cornea.
• If severe, may have complications, eg corneal ulcer.

Assessment^[2]

• How troublesome are the symptoms?
• Is there any corneal damage?
• Is there any other explanation for these symptoms and signs? (See Differential diagnosis, below.)
• Is there any underlying cause for the dry eye? (See above list.)
• What treatment has already been tried?
• Are there any aggravating or risk factors?
• Severity can be formally graded (usually in secondary care) by use of symptom questionnaire, tear break-up time test and examination of cornea (see 'Investigations and diagnosis', below).^[1]

Investigations and diagnosis^[1]

• Tear film can be assessed by tear break-up time or carrying out the Schirmer's test (usually in a secondary care setting).
• Corneal damage is assessed by staining with dyes, eg rose Bengal, lissamine green or fluorescein.^[4]
• However, these test results do not necessarily correlate well with symptom severity.
• Symptom questionnaires are available in the Canadian guidelines.^[1] These assist in grading the severity of dry eyes.

Investigations for underlying causes, eg serology for circulating auto-antibodies, may be indicated.^[3]

Tear break-up time^[4]

This simple test needs the use of a slit lamp, set on a bright-light setting with a cobalt blue filter.

• Instil fluorescein into the lower fornix.
• Ask the patient to blink several times and then stop.
• Measure the time between the last blink and the first appearance of a dark spot on the cornea (formation of a dry area).

A tear break-up time of <10 seconds suggests dry eyes.

Schirmer's test^[4]

• Instil a drop of local anaesthetic (optional).
• Prepare a filter paper (5 mm x 35 mm with folded end).
• Gently dry the eye.
• Apply the filter paper with the folded end hooked on to the lower lid margin at the junction between the middle and outer third (take care not to touch the cornea).
• Tell the patient to keep their eye open and to blink normally.
• Measure the amount of wetting after five minutes: wetting of <6 mm (with local anaesthetic) or <10 mm (without anaesthetic) indicates dry eye.
• Protect the eye if local anaesthetic was used.

Differential diagnosis^[2][3]

• Other causes of Red Eye - see separate article. Dry eyes tend to be a bilateral condition, even if one eye is more affected than the other.
• Allergy or irritation.
• Blepharitis - this often co-exists with a degree of dry eye.
• Entropion (eyelid turned in).
• Floppy eyelid syndrome - floppy and easily everted upper eyelids associated with chronic papillary conjunctivitis of the upper palpebral conjunctiva.^[5]

Treatment aims^[2]

• To ease discomfort.
• To protect and preserve the cornea.
• To treat any underlying conditions.

Management

Initial management - mild disease^[2][4]

• Explain the protracted nature of this condition and the importance of the patient's input in managing it.
• Many of these patients suffer with concurrent blepharitis and good lid hygiene measures can go some way towards alleviating both problems (see separate Blepharitis article).
• Reduce aggravating factors:
  • Review medication.
  • Reduce cigarette smoking or secondhand smoke.
  • Avoid draughts (use shields if necessary) and low humidity (humidifiers can help).
  • Regular breaks from computer work and reading, and encourage blinking. Lowering the computer screen to below eye level can decrease lid aperture.
  • Minimise contact lens wear.^[2]
• Treat underlying conditions, eg allergies, dermatoses.
• Tear substitutes - drops, gels and ointments (see box). The choice depends on patient preference and sensitivity to preservatives, etc.

Further management - moderate or severe disease^[1][2][4]

If things do not settle, use preservative-free tear substitutes and refer for further management, which includes:

• Increasing dietary omega-3 fatty acids (oily fish or supplements).
• Anti-inflammatory agents - these may be more effective than tear substitutes:
  • Topical ciclosporin A - useful, as there are no systemic effects with topical use.
  • Topical steroids - long-term use is limited by side-effects.
  • Oral tetracyclines - have both antibacterial and anti-inflammatory effects. Where these are not tolerated, clarithromycin or azithromycin may be used. Dose regimes are suggested in the literature.^[1]
• Ocular insert:
  • Slow-release rods of lubricant inserted into the conjunctival sac - but may cause discomfort.
• Punctal plugs:
  • Temporary or permanent occlusion of lacrimal ducts to reduce tear drainage (various methods available).^[7]
  • Inflammation should be controlled first.
• Moisture retention:
  • 'Bandage' contact lenses - protect and hydrate the cornea.
  • Scleral lenses - create a tear-filled reservoir.
  • Moisture-retaining goggles.
• Secretagogues:
  • Pilocarpine can improve symptoms but side-effects can be problematic.
• Autologous serum tears:
  • Serum contains various nutritive and anti-inflammatory agents and no preservatives. The serum can be frozen and stored for use as eye drops.^[8]
  • Usually reserved for severe cases.
• Surgery:
  • Tarsorraphy.
  • Conjunctival surgery, eg conjunctival graft or transplant, amniotic membrane transplant, salivary gland autotransplantation.

Complications^[2]

• Dry eyes are more susceptible to conjunctivitis.
• If severe, dry eye can lead to keratitis, corneal ulceration and infection, and corneal perforation (rare).

Prognosis^[2]

There is little formal research into the natural history of the condition, but it tends to follow a protracted course. The prognosis depends on the underlying cause if there is one. Loss of vision and corneal ulcers are rare.