Introduction
Allergic conjunctivitis is one of the most common external ocular conditions encountered in a general ophthalmic practice. Pediatricians, general practitioners, and internists also encounter patients with allergic conjunctivitis. The most common form is benign but is often a disruptive nuisance: work days may be missed and recreational activities abandoned. In rare circumstances, ocular allergies may lead to corneal damage with permanent loss of vision. Recognition of the forms of ocular allergy can lead to appropriate treatment and prevention of symptoms and ocular damage. The conditions that may be considered forms of ocular allergy include:
- Seasonal and perennial allergic conjunctivitis
- Atopic conjunctivitis and keratitis
- Atopic blepharitis
- Vernal conjunctivitis
Pathogenesis
The common factor in all ocular allergic conditions is the activation of mast cells in the lids and conjunctiva with release of inflammatory mediators and recruitment of other inflammatory cells. In seasonal allergic conjunctivitis this is the sole event responsible for the signs and symptoms. Histamine is released from pre-formed granules in the mast cell cytoplasm and arachadonic acid is synthesized from the phospholipids on the mast cell membrane, leading to the production of prostaglandins and leukotrienes. In chronic allergy, vernal conjunctivitis, and atopic conjunctivitis, eosinophils and lymphocytes are responsible for more severe ocular surface changes. Vision can be threatened when the corneal surface is disrupted by major basic protein, an epithelial-toxic protein released by eosinophils in the upper tarsal conjunctiva. More complex inflammatory responses also occur in chronic disease, with the release of cytokines from epithelial cells and fibroblasts on the ocular surface.
Clinical Findings
All allergic conditions of the eye produce itching. Without symptoms of itching, a different diagnosis should be considered. Other non-specific symptoms can occur including burning, irritation, and watery discharge. Clinical signs may be minimal with mild conjunctival hyperemia, minimal chemosis, and few papillae of the conjunctiva.
Seasonal allergic conjunctivitis occurs during times of high pollen counts. Typical patterns are trees in the early spring, grasses in the late spring and summer, grasses and weeds in the late summer and fall. In southern portions of the United States, various pollens can be found year round. Many patients have some rhinitis along with the ocular symptoms. Some rhinitis may be from excessive tears transported in to the nose via the nasolacrimal duct. Itching predominates. If patients rub their eyes then hyperemia and chemosis may be noticeable. Few papillae are noted. The cornea is almost never affected. Confusion with other causes of red eye can be reduced if the symptom of itching is present especially when pollen counts are high.
Perennial conjunctivitis has all the same features of seasonal allergic conjunctivitis but symptoms persist beyond the typical allergy seasons. This syndrome arises when sensitive individuals have frequent contact with animal dander, molds, or dust. These allergens can be present throughout the year. Some patients have multiple allergies to pollens as well as perennial allergens. These patients may be atopic, with an immune dysregulation. Patients suffering with perennial conjunctivitis or atopic conjunctivitis often benefit from consultation with an allergist.
Atopic conjunctivitis is a disease of adults with immune dysfunction leading to the production of IgE molecules that recognize many allergens. This is a chronic condition that can lead to severe ocular symptoms and corneal changes. The cornea may become ulcerated and scarred, leading to permanent visual loss. Almost all atopic patients will have one or more of the following: conjunctivitis, eczema (sometimes of the eyelids), rhinitis, and asthma. Because the conjunctival mast cells degranulate repeatedly over months and years, there is recruitment of eosinophils and lymphocytes and stimulation of fibroblasts. The consequence is possible conjunctival cicatrization, corneal ulceration and corneal vascularization. In addition to conjunctival hyperemia and chemosis, giant papillae can form on the upper palpebral conjunctiva and at the limbus. Every effort must be made to control the disease before the corneal changes occur.
Vernal conjunctivitis is a disease of childhood that shares many of the clinical features of atopic conjunctivitis and keratitis. The disease does not continue into adulthood, but some of these patients may develop atopic conjunctivitis later in life. Classically, the symptoms begin in the spring and recede in the fall and winter. Itching is severe, often accompanied by a ropy discharge and giant papillae of the upper palpebral conjunctiva. In darker skinned patients the limbus is commonly involved as well. Prolonged rubbing accompanied by the release of major basic protein from eosinophils in the giant papillae may result in corneal epithelial disruption and formation of a shield ulcer.
Treatment
Treatment of allergic conjunctivitis varies depending on the severity of the disease. All patients should be instructed to avoid allergens whenever possible. Since pollens are brought to the face by the hands in great quantities, it is critical to avoid eye and nose rubbing (even when the eyes and nose itch.) Eye rubbing may also cause mechanical degranulation of mast cells with release of inflammatory mediators. Simple treatments such as cold compresses to the eyes, feel good and may relieve the need to itch. Artificial tears are soothing. They wash out pollens and mediators from the tear film.
Over-the-counter antihistamine-vasoconstrictor combinations provide some relief but most of the effect is related to the washing effect of the vehicle. The antihistamines in these preparations are quite weak in comparison to newer products. The vasoconstrictors do a good job of whitening the eyes temporarily but exhibit tachyphylaxis, with progressively shorter duration of action during prolonged use. Rebound hyperemia may occur but this is controversial. With better products available, the best feature of these agents is their low cost.
Potent antihistamines are available and provide excellent relief of ocular itching. These include levocabastine (Livostin), olopatadine (Patanol), and emadastine (Emadine). They are extremely safe and can be used from one to four times a day for many months.
Topical nonsteroidal agents such as ketorolac (Acular) and diclofenac (Voltaren) are effective at reducing itching as well as other nonspecific ocular symptoms such as burning and irritation. Patients with multiple symptoms may benefit from these agents. They are when used one to four times a day for many months.
Mast cell stabilizers such as cromolyn sodium (Crolom and Opticrom) and lodoxamide (Alomide) are best prescribed for patients with chronic disease or in advance of the allergy season. They take some time to work and will not eliminate all symptoms in most patients. They are extremely safe and especially helpful for patients with perennial, atopic, or vernal conjunctivitis. They may be prescribed for years, and should be used at least twice a day. Most patients do best with drops four times a day initially.
Topical corticosteroids must be used whenever the cornea is threatened, to suppress inflammation and allow the mast cell stabilizers to take effect. Children with vernal conjunctivitis also need steroid drops when they present in the spring to control their severe symptoms. Newer products such as lotoprednol (Alrex) may be helpful with less elevation of intraocular pressure compared to stronger corticosteroids. Steroids should be tapered as quickly as possible.
Cyclosporin can reduce conjunctival inflammation safely and reliably, but the preparation from the IV or oral products causes pain on application. Newer, more comfortable vehicles are needed. Oral antihistamines can be helpful but the side effect of decreased tear production can exacerbate some ocular symptoms. Many patients with severe disease require multiple drops in combination.