OVERVIEW

What is allergic conjunctivitis?

Allergic conjunctivitis is the most common ocular allergic disease, sharing the same pathogenesis with other allergic conditions. It often coexists with allergic rhinitis, and when both occur together, it is termed allergic rhinoconjunctivitis. The main symptoms include itchy eyes, tearing, and redness. Topical antihistamines are commonly used for treatment, while corticosteroids are generally avoided.

How common is allergic conjunctivitis?

It is relatively common, affecting approximately 25% of the population.

What are the common types of allergic conjunctivitis?

Based on the timing of onset, allergic conjunctivitis is classified into three common types: acute allergic conjunctivitis, seasonal allergic conjunctivitis, and perennial allergic conjunctivitis:

• Acute allergic conjunctivitis is a sudden hypersensitivity reaction triggered by environmental exposure (often to known allergens, such as cat dander). Symptoms appear rapidly and typically resolve within 24 hours after allergen removal. It is characterized by intense itching, redness, tearing, conjunctival swelling, and eyelid edema.
• Seasonal allergic conjunctivitis: Accounts for 80% of all ocular allergy cases and is more noticeable than perennial allergic conjunctivitis. Typical allergens include tree and weed pollens.
• Perennial allergic conjunctivitis: Occurs year-round due to airborne allergens such as house dust mites, animal dander, and mold.

Which department should I visit for allergic conjunctivitis?

First, consult an ophthalmologist to rule out other conditions and confirm the diagnosis of allergic conjunctivitis. If confirmed, you may then visit a dermatology department for allergen testing.

SYMPTOMS

What are the common manifestations of allergic conjunctivitis?

Allergic conjunctivitis is usually easy to identify, typically presenting with simultaneous symptoms in both eyes, including itching, tearing, redness, edema of the bulbar conjunctiva (white part of the eye), and eyelid swelling.

Eye itching is a key clinical feature. Children may frequently rub their eyes, which can worsen the itching. In rare cases, eye swelling may occur, making it difficult to open the eyes.

What serious consequences can allergic conjunctivitis cause?

If symptoms like itching, tearing, and redness persist and worsen without timely treatment, vigorous eye rubbing may lead to secondary bacterial conjunctivitis, keratitis, or even severe complications such as lens dislocation and retinal detachment.

CAUSES

What causes allergic conjunctivitis?

Like other allergic diseases, common allergens can trigger allergic conjunctivitis.

The most frequent triggers are inhaled allergens, including various dust mites (house dust mites and storage mites are the most common), molds (such as Alternaria, Aspergillus niger, Bacillus, etc.), insect droppings and body fragments (e.g., cockroaches), grass pollens (ragweed, mugwort, hops, stinging nettle, sunflower, etc.), tree pollens (juniper, white ash, elm, mulberry, willow, plane tree, etc.), and animal dander (cat hair, dog hair, wool).

A small number of allergic conjunctivitis cases are caused by food, medications, or other allergens.

Who is more likely to develop allergic conjunctivitis?

Allergic conjunctivitis is related to individual constitution. People with other allergic conditions, such as allergic rhinitis, asthma, or skin allergies, have a higher risk of developing allergic conjunctivitis. If one or both parents have allergic diseases or there is a family history of allergies, the person is also more likely to suffer from allergic conjunctivitis.

Is allergic conjunctivitis contagious?

No, it is not contagious. However, multiple people in the same household or workplace may develop allergy symptoms simultaneously, often mistaken as transmission. In reality, it occurs because they share the same environment and are exposed to the same allergens, leading to similar allergic conjunctivitis reactions.

Therefore, if allergic conjunctivitis occurs, the first step should be to eliminate allergens. Ensure indoor ventilation, remove odorous objects or items (such as bedding), and wash and replace them regularly to prevent eye discomfort caused by allergic conjunctivitis.

DIAGNOSIS

What tests are needed for allergic conjunctivitis?

• Allergen testing: Includes skin prick tests and serum-specific IgE tests.
• Conjunctival secretion smear examination: Checks for the presence of characteristic cells in allergic conjunctivitis, such as eosinophils.

What is the purpose of allergen testing? What precautions should be taken?

Allergen testing is mainly used to identify specific allergens so that patients can avoid exposure in daily life.

• Skin prick test:

  • Primarily screens for common inhalant and food allergens. The allergens tested are usually those commonly encountered in daily life. The types of allergens tested may vary by hospital, with some hospitals able to test for dozens of allergens, though not all possible allergens can be covered.

  • Precautions: Discontinue antihistamines (e.g., loratadine, cetirizine, chlorpheniramine) and medications containing antihistamine ingredients (e.g., common cold remedies) 3–5 days before the test.

• Serum-specific IgE test:

  • Mainly assists doctors in assessing the severity of a patient's allergy to a specific allergen. Generally, higher IgE concentrations indicate a higher allergy level and more severe symptoms.

  • Precautions: Serum-specific IgE testing is not affected by medications, so no discontinuation of drugs is required. Fasting is also unnecessary on the day of the blood draw.

Which diseases can allergic conjunctivitis be easily confused with?

• Acute infectious conjunctivitis: Caused by viral or bacterial infections.

• Vernal keratoconjunctivitis: Common in children and adolescents, with males more frequently affected than females. Severity varies seasonally, often worsening in hot, dry climates. Intense itching, photophobia, and sticky discharge are common symptoms.

• Atopic keratoconjunctivitis: A chronic, bilateral, severe form of conjunctivitis associated with atopic dermatitis. About 25% of adults with atopic dermatitis may develop this condition, often preceded by skin symptoms and eyelid eczema.

• Giant papillary conjunctivitis: Now common, caused by prolonged exposure to foreign bodies, such as long-term contact lens wear. Prosthetic eyes or surgical sutures rubbing the eye may also trigger it.

• Dry eye syndrome: Results from reduced tear production and decreased tear film stability. Allergic conjunctivitis itself can worsen dry eye symptoms, often coexisting with it and leading to confusion between the two conditions.

TREATMENT

How to treat allergic conjunctivitis?

First, identify the allergen and then remove or try to avoid known allergens as much as possible.

Second, try non-drug treatments, such as cold compresses or rinsing the eyes with artificial tears.

Third, undergo symptomatic drug treatment under a doctor's guidance.

The most common approach is topical medication, such as eye drops or ointments, like emedastine eye drops or olopatadine hydrochloride eye drops.

Additionally, systemic medication (oral or intravenous) may also be used, but topical treatment is generally more effective than oral medication and more convenient than IV therapy.

If allergic rhinitis is also present, nasal treatment can significantly relieve eye symptoms. If other allergic conditions coexist, they should also be actively treated.

If needed, desensitization therapy may also be considered.

What are the adverse effects of medications for allergic conjunctivitis?

• The most commonly used drugs are antihistamines, with drowsiness being the main side effect. Therefore, avoid driving, operating precision instruments, or working at heights after taking them. Antihistamines also reduce tear production, which may cause or worsen dry eye symptoms.
• Topical corticosteroid eye drops may affect intraocular pressure. Hormonal treatments should be avoided unless other anti-allergy drugs are ineffective. During treatment, intraocular pressure should be measured monthly and evaluated annually.
• Topical eye medications may cause chemical irritation and discomfort.

Does allergic conjunctivitis require follow-up visits?

Yes.

Patients with allergic conjunctivitis need long-term supervision and medication guidance from specialists. For example, those receiving topical steroid treatment require regular intraocular pressure monitoring. Those undergoing specific immunotherapy (desensitization) also need periodic follow-ups.

Some may also need regular allergen testing to check for new sensitivities.

DIET & LIFESTYLE

What should patients with allergic conjunctivitis pay attention to in their diet?

• If the symptoms of allergic conjunctivitis are caused by an allergic reaction to a certain food, that food should be avoided.
• During acute allergic episodes, it is advisable to moderately reduce the intake of spicy or irritating foods and avoid alcohol to prevent worsening discomfort symptoms.

What should patients with allergic conjunctivitis pay attention to in daily life?

The primary focus should be on effectively avoiding or minimizing exposure to allergens.

For those allergic to dust mites:

• Wash bed sheets, pillowcases, and curtains frequently, using water at 60°C or higher to kill dust mites.
• Use mattress covers. On sunny days, expose quilts outdoors for at least half an hour, and discard old cotton padding that has been used for years.
• Avoid using carpets at home as much as possible.
• Minimize the use of plush toys for allergic children. Reduce decorative items that easily accumulate dust.
• Maintain indoor air circulation and sunlight exposure.
• Clean the house regularly, wear a mask while cleaning, and use a high-efficiency vacuum cleaner.

For those allergic to pollen:

• Avoid going outdoors during pollen season (pollen density tends to be higher on sunny and windy days).
• Wear a mask and transparent goggles when going out during pollen season. Change into clean clothes after returning home, and wash hair or wipe it with a damp towel.
• Keep windows closed while driving or indoors.
• Do not hang clothes outside during pollen season.
• Start taking anti-allergy medications one month before pollen season to prevent pollen allergies.

For those allergic to mold:

• Avoid placing too many indoor plants and overwatering them, as damp soil is an ideal environment for mold growth.
• Monitor indoor humidity levels, keeping them between 50% and 60%.
• Ensure indoor air circulation and keep bathrooms and kitchens dry.

For those allergic to animal dander:

• The ideal choice is to avoid keeping pets indoors and stay away from other pets as much as possible.

PREVENTION

Can allergic conjunctivitis be prevented?

Identifying and avoiding personal allergens as much as possible can help prevent the occurrence of allergic conjunctivitis.