Allergic conjunctivitis

What is allergic conjunctivitis?

The term conjunctivitis refers to inflammation of the conjunctiva. When this is caused by an allergic reaction it is called allergic conjunctivitis.

The most common form is a type 1 hypersensitivity reaction, which gives rise to seasonal or perennial allergic conjunctivitis.

Other types of allergic conjunctivitis are described here but their management is generally guided by an ophthalmology team. See also separate Eye Drugs - Prescribing and Administering (notes about eye drop allergies); Conjunctivitis (viral and less common types of conjunctivitis); Infective Conjunctivitis; Ophthalmia Neonatorum (conjunctivitis in the newborn); Diagnosing Conjunctival Problems (including trauma, lesions, degenerative conditions, etc) articles.

Although allergic conjunctivitis does not harm vision or cause lasting damage, it can have a significant impact on quality of life during the acute episode.¹

How common is allergic conjunctivitis? (Epidemiology)²

• Allergic conjunctivitis is estimated to affect up to 40% of the population. However, accurate estimates are difficult as many people with allergic conjunctivitis self-medicate and it is often underdiagnosed.

• Most cases are seasonal and typically occur in spring and summer. More than half of cases of allergic conjunctivitis are classified as seasonal or intermittent (less than 4 weeks in duration).

• Allergic conjunctivitis is common in children.

• Between 30–71% of patients with allergic rhinitis also have allergic conjunctivitis or conjunctival symptoms.

• Estimates of the prevalence of vernal keratoconjunctivitis in European countries range from approximately 1 in 10,000 people (in Nordic countries) to 3 in 1000 people (in Italy). It is more common in males.

• The prevalence of allergic conditions, including seasonal and perennial allergic conjunctivitis, has been increasing over the past few decades. The cause of this is not known.

Presentation of allergic conjunctivitis²

Allergic conjunctivitis presents with an intense itch or a burning sensation, a feeling of grittiness in the eyes and mild photophobia.

History

Ask about factors in the history which suggest an allergic cause.

• These include likely exposure to allergens and irritants such as chemicals, eye drops, potential chemical irritants (including eye make-up).

• Environmental allergens are suggested by symptoms which vary with seasonality, time of day, geography and nature of landscape (eg, rural, urban, oceanic).

• Contact lens use is also relevant, especially if there is poor lens hygiene.

Associated conditions which support an allergic cause include atopy, idiopathic urticaria, non-hereditary angio-oedema, and food allergies.

Findings

• Red eyes, usually bilateral, and often with a clear watery discharge.

• Oedema may be visible in round swellings on the inside of the eyelid.

• Lid swelling and/or oedema.

• Conjunctival injection.

• Discharge, if present, is usually watery.

• Skin irritation may be visible on the lids in contact dermatoconjunctivitis.

• Conjunctival chemosis with giant papillae (>1 mm) may be seen in contact lens or prosthesis users. In these cases there may be decreased lens tolerance and a mucous discharge.

Differential diagnosis

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

• Infective conjunctivitis: viral or bacterial.

• Blepharitis.

• Uveitis.

• Acute glaucoma.

• Keratitis: presents with a unilateral, acutely painful, photophobic, injected eye.

• Scleritis: severe, boring ocular pain, which may radiate to the head and face.

• Episcleritis: mildly uncomfortable acute-onset red segment in one or both eyes.

• Orbital cellulitis.

• Foreign body

• Ocular herpes simplex.

• Herpes zoster ophthalmicus.

• Dry eye syndrome.

• Inflamed pterygium/pinguecula (see the separate Diagnosing Conjunctival Problems article).

• Arc eye/snow blindness/retinal burns (see the separate Eye Injuries article).

Diagnosing allergic conjunctivitis (investigations)

Diagnosis is usually made on history and eye examination. This should include fluorescein staining, testing visual acuity, checking the anterior chamber for clarity (with a handheld ophthalmoscope) and everting the lids to examine the undersides and check for foreign bodies.

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 testing against specified allergens (RAST).

Types of allergic conjunctivitis

There are six recognised types of allergic conjunctivitis: seasonal, perennial, drug-induced, contact lens-induced, vernal and atopic.³

Seasonal, perennial, drug-induced and contact lens-induced conjunctivitis are caused by type 1 hypersensitivity reactions; vernal and atopic conjunctivitis are addressed separately below.

Conjunctivitis due to type 1 hypersensitivity reactions

• Seasonal conjunctivitis (conjunctivitis associated with hay fever). The most common allergen is pollen. Grass pollens peak from May to August, whereas tree pollens tend to peak on either side of this period, depending on the tree species involved. Individual patients may have multiple allergies; however, their symptoms tend to recur at the same time each year.

• Perennial conjunctivitis, where symptoms occur throughout the year in response to various allergens such as animal dander and house dust mites. Symptoms are typically worse in the mornings.

• Giant papillary conjunctivitis - common causes include contact lenses and, following eye surgery, (broken) sutures and prostheses. Giant papillary conjunctivitis is the most severe form of contact lens-associated papillary conjunctivitis. It is seen in contact lens and prosthesis users. 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 does not respond to antihistamines and mast cell stabilisers.

Management of allergic conjunctivitis

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.^{4 5}

Many patients self-treat and go for help only when basic measures have failed.¹

In milder cases, it is worth trying the following before considering drug treatment:

Non-pharmaceutical management⁵

• Avoid rubbing the eyes.

• Cool compresses, eye baths and preservative-free lubricants may be soothing.

• Avoid wearing contact lenses/prostheses until symptoms and signs resolve.

• If lenses are essential, use daily disposable lenses.

• Allergen avoidance is often tricky but should be the primary aim. Consider introducing air conditioning and ventilation, reducing pet contact, reducing carpet thickness and quantity in favour of hard floors, and regular bedding change.

• Artificial tears can be helpful in mild cases (they dilute the allergen).

• Contact lenses should not be worn if conjunctivitis is present or during a course of topical therapy.

Pharmaceutical management⁵

• Topical mast cell stabilisers. These are recommended for use throughout a period of allergen exposure. Sodium cromoglycate is usually effective but newer agents, such as lodoxamide and nedocromil, may be effective in those with an inadequate response to sodium cromoglycate.

• Topical antihistamines (other than in contact dermatoconjunctivitis which is unresponsive to these). The topical ocular antihistamines, antazoline and azelastine, provide rapid relief of the symptoms of allergic conjunctivitis. Azelastine may have additional mast cell stabilising properties.⁶ Topical antihistamines are not appropriate for prolonged use (no longer than six weeks).

• Combined antihistamine/vasoconstrictor drops - eg, antazoline with xylometazoline.

• Topical ocular diclofenac can be prescribed as adjunctive therapy if further symptomatic relief is required.

• Oral antihistamines such as loratadine or chlorphenamine. Oral antihistamines provide relief of symptoms and are particularly useful when there is associated allergic rhinitis. They can cause drowsiness, particularly the older compounds such as chlorphenamine. Patients need to be cautioned regarding this.

• Topical corticosteroids may be an option for very severe symptoms but should ONLY be started after examination by a ophthalmologist.⁷ Steroid drops carry increased risks of infections (including the risk of worsening undiagnosed corneal herpes simplex or ocular herpes zoster), and of secondary glaucoma. Long-term use is avoided because this can result in cataract, glaucoma, and severe bacterial or fungal infections involving the eyelid, conjunctiva and cornea.

• Intranasal corticosteroids have been shown to reduce ocular symptoms.⁸

Referral²

Arrange urgent assessment by ophthalmology if:

• Features suggestive of a serious cause of red eye.

• Suspected periorbital or orbital cellulitis.

• Severe disease - eg, corneal ulceration, significant keratitis, or presence of pseudomembrane.

• Recent intraocular surgery.

• Conjunctivitis associated with a severe systemic condition such as rheumatoid arthritis or other reasons for immunocompromise.

• Corneal involvement associated with soft contact lens use. Do not give antibiotics in the interim as this may interfere with corneal culture. Advise the person to take their contact lenses with them to eye casualty as special diagnostic tests may be required.

• Neonate with red sticky eye (suggesting ophthalmia neonatorum).

Discuss with or refer to ophthalmology (urgency dependent on clinical situation) if:

• Diagnostic uncertainty or the appropriate diagnostic equipment is not available.
  Suspected atopic keratoconjunctivitis, vernal keratoconjunctivitis, or giant papillary conjunctivitis.

• Suspected mild papillary conjunctivitis due to contact lens wear (assessment by an optometrist for modification of contact lens use is needed, and specialist management by an ophthalmologist is required for more severe cases).

• Severe or resistant allergic conjunctivitis (atopic keratoconjunctivitis and vernal keratoconjunctivitis must be excluded). Resistant cases of perennial and seasonal allergic conjunctivitis may require specialist treatments, such as topical corticosteroids or immunotherapy.

Consider referral to an allergy specialist if:

• Multisystem disease (eg, nasal and respiratory symptoms). Allergen identification may help with avoidance.

• Symptoms interfere significantly with quality of life and ability to function.

Complications of allergic conjunctivitis

Serious complications are very rare in the majority of cases of allergic conjunctivitis; however, a severe allergic reaction can lead to corneal ulceration.

Prognosis²

• Most people with allergic conjunctivitis respond well to treatment although seasonal exacerbations can occur.

• Vernal conjunctivitis generally resolves spontaneously after puberty, although complications such as corneal ulcers, cataract and glaucoma can lead to permanent visual impairment.

• Atopic keratoconjunctivitis is a chronic disease which persists for years. Corneal complications which can be sight-threatening have been reported in 60-70% of people.

Vernal conjunctivitis³

This is an uncommon IgE- and cell-mediated allergic condition, mainly affecting boys (usually after the age of 5 years) and young individuals (there is no gender bias post-puberty), living in warm conditions. 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.

Vernal conjunctivitis may be seasonal or perennial and it is often more pronounced in the spring months.

Consider the diagnosis in patients not responding to conventional treatment.⁹ A new grading system has 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).

• Associated keratoconus (possible cause, possible effect) and other types of corneal malformations.

Suggestive symptoms

• Intense itching.

• Thick ropey mucous discharge.

Signs

• 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.

• 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 suspected vernal conjunctivitis to ophthalmologists, as management is specialised and serious corneal complications can occasionally occur.

• Topical steroids may need to be added to conventional anti-inflammatory treatment.

• Systemic therapy with steroids ± ciclosporin may sometimes be needed.

• Aspirin may be of benefit in older children.

• Systemic antivirals may be added to the treatment regime if immunosuppressants are used, as these patients are vulnerable to herpes simplex keratitis.

• Permanent relocation to a cooler climate is a very effective therapy for vernal conjunctivitis although, clearly, this is not often practicable.

Atopic conjunctivitis¹¹

This is a relatively rare but potentially serious condition affecting mainly young individuals (onset: age 25-30 years) who have atopic dermatitis. Presentation can be similar to vernal conjunctivitis but the condition 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.

Signs

• 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.

Management

Referral to ophthalmology, where the approach is similar to that for vernal conjunctivitis. This condition is associated with a higher rate of corneal scarring than vernal conjunctivitis and needs specialised care.³

Dr Mary Lowth is an author or the original author of this leaflet.