Allergic conjunctivitis (AC) is inflammation of the conjunctiva (the membrane covering the white part of the eye) due to allergy. Although allergens differ among patients, the most common cause is hay fever. Symptoms consist of redness (mainly due to vasodilation of the peripheral small blood vessels), edema (swelling) of the conjunctiva, itching, and increased lacrimation (production of tears). If this is combined with rhinitis, the condition is termed allergic rhinoconjunctivitis (ARC).
The symptoms are due to the release of histamine and other active substances by mast cells, which stimulate dilation of blood vessels, irritate nerve endings, and increase secretion of tears.
Treatment of allergic conjunctivitis is by avoiding the allergen (e.g., avoiding grass in bloom during "hay fever season") and treatment with antihistamines, either topical (in the form of eye drops), or systemic (in the form of tablets). Antihistamines, medications that stabilize mast cells, and nonsteroidal anti-inflammatory drugs (NSAIDs) are generally safe and usually effective.
Itching is the most typical symptom of ocular allergy, and more than 75% of patients report this symptom when seeking treatment.
A study by Klein et al. showed that in addition to the physical discomfort allergic conjunctivitis causes, it also alters patients' routines, with patients limiting certain activities, such as going outdoors, reading, sleeping, and driving.
- Pollen from trees, grass, and ragweed
- Animal skin and secretions such as saliva
- Perfumes
- Cosmetics
- Skin medicines
- Air pollution
- Smoke
- Dust mites
- Balsam of Peru (used in food and drink for flavoring, in perfumes and toiletries for fragrance, and in medicine and pharmaceutical items for healing properties)
- Eye drops (A reaction to preservatives in eye drops can cause toxic conjunctivitis)
- Contact lens solution (some preservatives can irritate the eye over time, resulting in conjunctivitis)
- Contact lens (conjunctivitis is also caused by repeated mechanical irritation of the conjunctiva by contact lens wearers)
Most cases of seasonal conjunctivitis are due to pollen and occur in the hay fever season, grass pollens in early summer, and various other pollens and moulds may cause symptoms later in the summer.
Pathophysiology
thumb|250px|right|Eye with mild allergic conjunctivitis
The ocular allergic response is a cascade of events that is coordinated by mast cells. Beta chemokines such as eotaxin and MIP-1 alpha have been implicated in the priming and activation of mast cells in the ocular surface. When a particular allergen is present, sensitization takes place and prepares the system to launch an antigen-specific response. TH2 differentiated T cells release cytokines, which promote the production of antigen-specific immunoglobulin E (IgE). IgE then binds to IgE receptors on the surface of mast cells. Then, mast cells release histamine, which then leads to the release of cytokines, prostaglandins, and platelet-activating factor. Mast cell intermediaries cause an allergic inflammation and symptoms through the activation of inflammatory cells. SAC is the most common ocular allergy. Symptoms of the aforementioned ocular diseases include itching and pink to reddish eye(s).
Management
A detailed history allows doctors to determine whether the presenting symptoms are due to an allergen or another source. Diagnostic tests, such as conjunctival scrapings to look for eosinophils, help determine the cause of the allergic response.
Dual Activity Agents
Dual-action medications are both mast cell stabilizers and antihistamines. They are the most commonly prescribed class of topical anti-allergy agents. Olopatadine (Patanol, Pazeo) and ketotifen fumarate (Alaway or Zaditor) are both commonly prescribed. Ketotifen is available without a prescription in some countries. However, studies demonstrates that olopatadine is more effective than ketotifen in reducing the itching associated with allergic conjunctivitis in the antigen challenge model.
Corticosteroids
Ester-based "soft" steroids such as loteprednol (Alrex) are typically sufficient to calm inflammation due to allergies, and carry a much lower risk of adverse reactions than amide-based steroids.
A systematic review of 30 trials, with 17 different treatment comparisons, found that all topical antihistamines and mast cell stabilizers included for comparison were effective in reducing symptoms of seasonal allergic conjunctivitis. There was not enough evidence to determine differences in long-term efficacy among the treatments. Allergy immunotherapy can be administered orally (as sublingual tablets or sublingual drops) or by injections under the skin (subcutaneous). Discovered by Leonard Noon and John Freeman in 1911, allergy immunotherapy represents the only causative treatment for respiratory allergies.
Experimental research has targeted adhesion molecules known as selectins on epithelial cells. These molecules initiate the early capturing and margination of leukocytes from circulation. Selectin antagonists have been examined in preclinical studies, including cutaneous inflammation, allergy, and ischemia-reperfusion injury. There are four classes of selectin blocking agents: (i) carbohydrate-based inhibitors targeting all P-, E-, and L-selectins, (ii) antihuman selectin antibodies, (iii) a recombinant truncated form of PSGL-1 immunoglobulin fusion protein, and (iv) small-molecule inhibitors of selectins. Most selectin blockers have failed phase II/III clinical trials, or the studies were stopped due to their unfavorable pharmacokinetics or prohibitive cost.