Epidemiology

• Allergies are thought to affect about 20% of the population and, of these, about 20% of individuals experience eye problems.^[2]
• Over 50% of patients who seek treatment for allergies present with ocular symptoms.^[3]
• Both perennial and seasonal allergic conjunctivitis are very common. Allergic conjunctivitis is the cause of around 15% of all eye problems presenting in general practice.^[4]
• Vernal keratoconjunctivitis occurs mainly in hot climates and presents more often in young males (see 'Vernal conjunctivitis', below).
• Seasonal allergic conjunctivitis and perennial allergic conjunctivitis are often associated with a family history of asthma, eczema or rhinitis.

Presentation

• Allergic conjunctivitis presents with an intense itch or a burning sensation and with mild photophobia.
• Ask about exposure to allergens - for example:
  • A history of contact with chemicals or eye drops.
  • A history with a seasonal time course.
• Ask about known allergies:^[5]
  • Major - hayfever, asthma, atopic dermatitis, eczema.
  • Minor - idiopathic urticaria, non-hereditary angioedema, food allergies.
• Look for bilateral red eyes, often with a clear watery discharge.
• Oedema in round swellings may be seen on the inside of the eyelid, and lid swelling.

Differential diagnosis

The diagnosis is usually straightforward but other causes of uncomfortable, inflamed eyes must be considered:

• Infective conjunctivitis: viral or bacterial.
• Blepharitis.
• Uveitis (iritis).
• Acute glaucoma.
• Keratitis: often presents with a unilateral, acutely painful, photophobic, intensely injected eye.
• Scleritis: severe, boring ocular pain, which may also involve the adjacent head and facial regions.
• Episcleritis: relatively asymptomatic acute-onset localised redness in one or both eyes.
• Orbital cellulitis.
• Foreign body.
• Ocular herpes simplex.
• Herpes zoster ophthalmicus.
• Dry eye syndrome.

Investigations

• The diagnosis can usually be based on a careful history and eye examination.
• Investigations and/or referral are only indicated if there is any doubt in the diagnosis.
• Investigations may include conjunctival swabs, skin prick testing, serum immunoglobulin E (IgE) and radioallergosorbent test (RAST).^[6]

Types of allergic conjunctivitis

Type I hypersensitivity reactions

• Essence - hypersensitivity reaction to specific allergens. There are four recognised types:
  • Seasonal conjunctivitis (aka conjunctivitis associated with hay fever), the most common allergen being pollen. This tends to recur at the same time each year, often in atopic individuals.
  • Perennial conjunctivitis, where symptoms occur throughout the year in response to various allergens such as animal dander and house dust mites. Symptoms may be worse in the mornings.
  • Giant papillary conjunctivitis - common causes include contact lenses, (broken) sutures and prostheses following eye surgery. This is the most severe form of contact lens-associated papillary conjunctivitis and, as such, is seen in contact lens and prosthesis users.^[5] However, the widespread use of disposable contact lenses has reduced its incidence.
  • Contact dermatoconjunctivitis which tends to arise in response to eye drops or cosmetics. It is characterised by a complete lack of response to antihistamines and mast cell stabilisers.
• Suggestive symptoms - itchy watery red eyes ± skin irritation in contact dermatoconjunctivitis. Wearers of contact lenses may report decreased lens tolerance and mucous discharge in giant papillary conjunctivitis.^[5]
• Signs to look for - lid oedema or conjunctival chemosis, papillae - may be giant (>1 mm) in contact lens/prosthesis users.
• Management - general measures include:
  • Avoiding wearing contact lenses/prosthesis until symptoms and signs resolve. If the patient has to wear lenses, daily disposable lenses, different lens material and mast cell stabilisers may help.
  • Avoiding rubbing the eyes.
  • Using cool compresses and preservative-free lubricants, which may also help.
  If severe, rapid relief can be obtained with an oral or topical antihistamine. For more long-term management, consider a topical mast cell stabiliser and oral or topical antihistamines (other than in contact dermatoconjunctivitis which is unresponsive to these). Corticosteroids can be used if symptoms are very severe^[7] but there must be absolutely no doubt about the diagnosis.

Patients experiencing giant papillary conjunctivitis following surgery should be referred to the ophthalmologists. Also, consider referral where contact dermatoconjunctivitis is severe or where an alternative eye drop needs to be prescribed (eg for glaucoma).

Vernal conjunctivitis^[8]

• Essence - this is an uncommon IgE and cell-mediated allergic condition, mainly affecting boys (usually after the age of 5) and young individuals (there is no gender bias post-puberty), living in warm conditions.^[8] It rarely persists beyond the age of 25 years. Its incidence is decreasing among the white population but increasing among Asians. It is most common in Arabs and Afro-Caribbeans.^[5] It may be seasonal or perennial, and is often more pronounced in the spring months.^[9] Think of this in patients not responding to conventional treatment.^[4] A new grading system has recently been developed to indicate the severity of this disease, ranging from 0 (absence of symptoms and no therapy) to 4 (severe disease involving the cornea and needing pulsed high-dose topical steroid).^[10]
• Risk factors - atopy (patient or family history in over 80% of cases),^[6] associated keratoconus (possible cause, possible effect) and other types of corneal malformations.
• Suggestive symptoms^[11] - intense itching, thick ropey mucous discharge.
• Signs to look for^[11] - large cobblestone upper lid papillae (if these are very large, they may cause a mechanical ptosis), raised white mucoid nodules arranged around the limbus (margin) of the cornea. There may be an associated keratitis (in the form of little epithelial erosions, seen as tiny dots on slit lamp examination with a fluorescein stain or in the form of an ulcer).
• Management - refer to ophthalmologists, as topical steroids may need to be added to conventional treatment for allergic conjunctivitis and, occasionally, serious corneal complications can occur from this disease. Rarely, systemic therapy with steroids ± ciclosporin is needed and aspirin may be of benefit in older children.^[5] Systemic antivirals may be added to the treatment regime if immunosuppressants are used, as these patients are vulnerable to herpes simplex keratitis.^[6] It may be worth noting that permanent relocation to a cooler climate is a very effective therapy for vernal conjunctivitis^[9] although, clearly, this is not practicable in many cases.

Atopic conjunctivitis^[8]

• Essence - a relatively rare but potentially serious condition affecting mainly young individuals (onset: 25-30 years old)^[6] suffering from atopic dermatitis. Presentation can be similar to vernal conjunctivitis but persists for years and is associated with significant visual morbidity secondary to keratoconus, presenile cataract and occasionally, retinal detachment.
• Suggestive symptoms - itching, redness, photophobia ± blurred vision.^[6]
• Signs to look for - red, thickened, scaly and occasionally fissured lids (lid eczema and blepharitis), cicatrisation of the conjunctiva in advanced cases, keratopathy (including keratoconus), evidence of concurrent infections such as herpes simplex virus (HSV) and microbial keratitis. Unlike vernal conjunctivitis, the discharge tends to be watery.^[9]
• Management - as for vernal conjunctivitis. This condition is associated with a higher rate of corneal scarring than vernal conjunctivitis.^[9]

Associated diseases

Allergic rhinitis may be associated with allergic conjunctivitis.

Management

The management of allergic conjunctivitis is aimed at preventing the release of mediators of allergy, controlling the allergic inflammatory cascade and preventing ocular surface damage secondary to the allergic response.^[2] Many patients start medicating themselves of their own accord^[1] and go for help when basic measures have failed. In milder cases, it is worth checking the following before considering drug treatment:

• Allergen avoidance is often tricky but should be the primary aim. Consider introducing air conditioning, reducing pet contact, bedding change.
• Cold compresses may be soothing.^[5]
• Artificial tears can be helpful in mild cases (they dilute the allergen).^[6]
• Contact lenses should not be worn if conjunctivitis is present or during a course of topical therapy.

Drugs

• The topical ocular antihistamines, antazoline, azelastine, and emedastine provide rapid relief of the symptoms of allergic conjunctivitis. Azelastine seems to have additional mast cell stabilising properties.^[3] Topical antihistamines are not appropriate for prolonged use (no longer than six weeks).
• Mast cell stabilisers are recommended for use throughout a period of allergen exposure. Sodium cromoglicate is usually effective but the newer agents, lodoxamide and nedocromil, may be effective in those with an inadequate response to sodium cromoglicate.
• Diclofenac eye drops are also licensed for seasonal allergic conjunctivitis.
• Topical corticosteroids should never be given for an undiagnosed red eye, when visual acuity is impaired, or if there is a history of ocular herpes simplex infection. There may be a role for intranasal corticosteroids which have been shown to reduce ocular symptoms.^[12] Ophthalmologists may use topical (occasionally systemic) corticosteroids in severe cases.^[7] Long-term use is avoided because this can result in cataract, glaucoma, and severe bacterial or fungal infections involving the eyelid, conjunctiva, and cornea.
• Oral antihistamines provide relief of symptoms and are particularly useful when there is associated allergic rhinitis.

Complications

Complications are very rare, but a severe allergic reaction can lead to corneal ulceration.

Prognosis

Prognosis is excellent with resolution over a variable time course.