Allergic conjunctivitis is an inflammation of the conjunctiva, a clear membrane covering the inner eyelids and the sclera, resulting from exposure to allergens.¹

Common environmental triggers include pollen, mold spores, dust, and animal dander, particularly prevalent during hay fever season.¹

Pathophysiology and risk factors

The immune system perceives allergens as threats, triggering the release of histamine and other inflammatory mediators. People with allergy histories are at higher risk for allergic conjunctivitis, especially during seasonal allergies.

Diagnosis¹

Diagnosis primarily relies on clinical history and examination. Key diagnostic signs include redness of the sclera and small papillae on the conjunctiva.

The allergic cascade

The allergic cascade in the eye is a series of events that occur when an allergen, such as pollen, animal dander, or dust, comes into contact with the eye. Here’s a step-by-step explanation of the process:

1. Allergen entry: An allergen enters the eye and binds to specific receptors on mast cells, which are immune cells located in the conjunctiva (the membrane covering the white part of the eye and the inside of the eyelids).⁴
2. Mast cell activation: The binding of the allergen to the H1 and H2 receptors on mast cells triggers these cells to become activated.⁴
3. Release of mediators: Activated mast cells release several chemical mediators, including histamine.⁴ Histamine is a key player in the allergic response and is responsible for many of the symptoms associated with allergic conjunctivitis.
4. Histamine effects:
   • Nerve stimulation: Histamine stimulates nerve endings in the eye, leading to itching.⁴
   • Vasodilation: Histamine causes the blood vessels in the eye to dilate (widen), resulting in redness.⁴
   • Vascular permeability: Histamine increases the permeability of blood vessels, allowing fluid to leak into surrounding tissues, which leads to swelling.⁴

Management

Management includes both non-pharmacological and pharmacological approaches:

Home care: Patients should avoid rubbing their eyes, use artificial tears, apply cool compresses, and maintain good hand hygiene. To reduce pollen exposure, wearing hats and sunglasses outdoors and showering after outdoor activities can help.

Pharmacological treatment: OTC antihistamine eye drops help reduce histamine H1, H2 and mast stabiliser release. Prescription drops containing ophthalmic H1 and H2 antagonists, as well as mast cell stabilisers offer effective relief.¹ Anti-inflammatory eye drops reduce inflammation, while vasoconstrictor eye drops help constrict congested vessels.¹

For severe cases, steroid eye drops are prescribed under medical supervision.¹ Epinastine hydrochloride prevents histamine binding to both the H1- and H2-receptors, and stabilises mast cells, providing fast relief from itching, lasting up to 12 hours.⁴ Allergic conjunctivitis is a widespread condition, impacting a significant portion of the global population. While the condition is manageable through avoidance strategies and pharmacological treatments, more severe cases may require specialist intervention.

Emerging therapies promise to further improve patient outcomes, offering relief from the debilitating effects of this allergic condition.²

References available on request