Submitted by Susan Herndon, OD, EyeOne
It‘s spring, and trees, plants and weeds are blooming, and pollen is in the air and coating our cars. Ocular allergies are becoming a common complaint in patient care.
Ocular allergies or Allergic Conjunctivitis refers to a spectrum of ocular disorders of the eyelid and conjunctiva. These range from Seasonal Allergic Conjunctivitis (SAC) and Perennial Allergic Conjunctivitis (PAC) also, Atopic Keratoconjunctivitis, Atopic Blepharconjunctivitis, Vernal Keratoconjunctivitis and Giant Papillary conjunctivitis. Non-complicated allergic eye disease comprises 95% of all ocular allergies.
Allergy is a form of hypersensitivity, a chronic condition involving an abnormal reaction to an ordinary harmless substance called an allergen. Four types of hypersensitivity reactions exist. Types I, II and III are antibody mediated. While type IV is mediated by T-cells and macrophages. Most ocular allergies result from either type I or Type IV hypersensitivity or combination of both.
Seasonal Allergic Conjunctivitis and Perennial Allergic Conjunctivitis
Seasonal Allergic Conjunctivitis (SAC) and Perennial Allergic Conjunctivitis (PAC) are the two most common forms of ocular allergy affecting up to 20% of the population. 90% of allergic conjunctivitis are SAC and 5% are PAC.
In Seasonal Ocular Allergies, symptoms are tied to the pollination of plants and tend to peak in spring, late summer, and fall. Symptoms recur but are self limiting every season.
In Perennial Ocular Allergies, symptoms are usually mild but persistent. Chronic exposure to allergens like house dust mites, mold and animal dander can cause PAC. If suspected, a work related allergy has to be confirmed by worsening of symptoms in the workplace. Smoke, pollutions or wind can also increase symptoms of ocular allergies.
Medical history is the first crucial step in the diagnosis of ocular allergies, especially in the differential diagnosis of a ‘red eye’. Medical history should cover types of symptoms (itching, burning, photophobia, discharge, visual changes and pain) whether unilateral or bilateral, duration of symptoms, presence of allergies or systemic diseases.
Previous treatments, family history, environmental and occupational exposures, use of contact lenses and any ocular medication and surgery are essential in the diagnostic considerations.
Signs and Symptoms
Signs and symptoms include itching, tearing, chemosis and conjunctiva injections, eyelid edema and papillary hypertrophy.
Ocular allergies are diagnosed typically by clinical history, signs and symptoms. There are mimics of ocular allergy that make the diagnosis difficult like tear film dysfunction (dry eye syndrome), blepharitis and toxic or mechanical conjunctivitis. Ocular allergy and dry eye syndrome are the most common ocular surface inflammatory disorders. One does not preclude the coexistence of the other.
Ocular itching is the hallmark symptom of ocular allergies. This indicates the release of histamine from conjunctival mast cells and the activation of H1 receptors on nerve endings. Eyelid itching frequently occurs in blepharitis patients especially if related to eyelid infestation.
Ocular redness (hyperemia) is the primary sign of ocular allergies due to conjunctiva vasodilation which is often diffuse.
Tearing or watery eyes is a nonspecific consequence of the lacrimal glands response reflex to several stimuli involving conjunctiva and nasal sensory nerve endings. Tearing is associated with ocular allergies but also other forms of ocular surface disease such as evaporative dry eye.
Edema is easy to observe when limited to eyelid swelling and can also involve the conjunctiva resulting in chemosis. This symptom is easy to observe if intense. When mild or moderate, a slit lamp exam is required.
Allergic patient may report mild visual disturbances like blurring this is usually a sign of corneal involvement. Bilateral involvement is typical for ocular allergies but Asymmetrical presentation are possible. Viral conjunctivitis is often unilateral at onset and becomes bilateral in 1-2 days.
Mast cell degranulation releases histamine into surrounding tissues. The binding of histamine to H1 and H2 receptors on conjunctiva nerves and small blood vessels produces itching, vascular dilation and influx of fluid into conjunctiva tissue. Histamine is only one of several preformed mediators that are released when a mast cell degranulates. Antihistamines are beneficial but do not block the effects on non histamine mediators. Dual acting mast cell stabilizes/antihistamines are the most effective medication for treatment of ocular allergies. The efficacy and safety profile of combination mast cell stabilizers and antihistamines suggests that the combination medications be first line agents for management of these conditions.
Refer to an ophthalmologist or optometrist especially in cases of severe symptoms, unilateral redness, ocular pain, visual disturbance, or long‐term use of topical drugs.
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