Conjuntivite alérgica.

INTRODUCTION — Allergic conjunctivitis is a relatively benign ocular disease that causes significant suffering and use of healthcare resources, although it does not threaten vision. Ocular allergy is estimated to affect at least 20 percent of the population on an annual basis, and the incidence is increasing.

CLINICAL MANIFESTATIONS — Allergic conjunctivitis is predominantly a disease of young adults, with an average age of onset of 20 years of age. Symptoms tend to decrease with age. Approximately one-half of patients have a personal or family history of other allergic conditions, such as allergic rhinitis, atopic dermatitis, and asthma.
- Signs and symptoms — Allergic eye disease primarily affects the conjunctiva. The signs and symptoms include itching, tearing, conjunctival edema, hyperemia, watery discharge, burning, and photophobia (picture 1). Eyelid edema is also common. Symptoms are usually bilateral; however, one eye can be affected more than the other.
- Laboratory findings — The diagnosis of allergic conjunctivitis is usually made clinically. A number of tests can be performed in patients suspected of having allergic conjunctivitis, although these are usually limited to academic or confirmatory purposes.
 Conjunctival scrapings
 IgE levels
 Mast cell activity

TYPES OF ALLERGIC CONJUNCTIVITIS — Allergic conjunctivitis can be subdivided into three specific conditions:
 Acute allergic conjunctivitis
 Seasonal allergic conjunctivitis (SAC)
 Perennial allergic conjunctivitis (PAC)
Each is associated with specific clinical features.
- Acute allergic conjunctivitis — Acute allergic conjunctivitis is a sudden-onset hypersensitivity reaction caused by environmental exposure, usually to a known allergen, such as cat dander.
- Seasonal allergic conjunctivitis — Seasonal allergic conjunctivitis (SAC) goes by several other names, including allergic conjunctivitis, hay-fever type conjunctivitis, or allergic rhinoconjunctivitis. It is a mild form of ocular allergy, and it is frequently associated with rhinitis. SAC typically has a less dramatic onset compared to acute allergic conjunctivitis, and a more predictable and chronic course that corresponds to one or more specific pollen seasons.
- Perennial allergic conjunctivitis — Perennial allergic conjunctivitis (PAC) is a mild, chronic, allergic conjunctivitis related to environmental exposure to year-round, usually indoor, allergens such as dust mites, animal danders, and molds.

DIAGNOSIS — The diagnosis of allergic conjunctivitis is made clinically based on suggestive signs and symptoms. Laboratory tests are generally not needed.
- Differential diagnosis — The differential diagnosis of these findings includes infectious conjunctivitis, blepharitis, and dry eye.
 Allergic conditions are often accompanied by significant itch, whereas this is not very common in infection.
 Allergic conjunctivitis principally affects the conjunctiva, whereas the principal target tissue in dry eye is the cornea. Corneal involvement is characterized by vital dye uptake. This test can readily be performed by an ophthalmologist.

GENERAL MANAGEMENT
- Basic eye care — In all types of allergic conjunctivitis, patients should not rub their eyes because that can cause mechanical mast cell degranulation and worsening of symptoms. Frequent use of artificial tears throughout the day can also help to dilute and remove allergens. During acute episodes of itching, patients should be instructed to use topical antihistamines, frequent artificial tears, and cool compresses. Avoidance or reduction of contact with known allergens and appropriate management of environmental exposure are key to effective management of allergic conjunctivitis, especially in more severe cases. This includes significant reduction (or even complete avoidance) of contact lens use, given the propensity of allergens to adhere to contact lens surfaces.
- Allergen avoidance — Avoidance of the allergen is the primary therapy whenever possible. Preventive steps to reduce symptoms of SAC include limiting outdoor exposure, use of air conditioning, and keeping car and home windows closed during the peak seasons.
- Allergy evaluation and immunotherapy — Referral to an allergy specialist for possible skin testing is indicated for severe allergic conjunctivitis that is not controlled adequately by standard therapy. Referral is also appropriate for the management of concurrent allergic rhinitis, asthma, or systemic allergic symptoms, regardless of severity.

STEPWISE APPROACH TO THERAPY
- Acute allergic conjunctivitis — If pharmacologic treatment is needed, then several options exist:
 Over-the-counter topical antihistamine/vasoconstrictors are usually sufficient in treating symptoms of short-duration (eg, less than two weeks).
 Oral, nonsedating, over-the-counter or prescription antihistamines are another option for occasional acute allergic conjunctivitis. However, topical agents are faster-acting and less likely to cause systemic side effects, and are therefore preferred when ocular symptoms are the main presenting problem.
 Single agent topical products (ie, decongestants or antihistamines only) are also widely available without a prescription, although the combination of an antihistamine and a vasoconstrictor works better than either agent alone [19].

- Frequent episodes — For frequent attacks of acute allergic conjunctivitis (ie, occurring more than two days per month), a topical medication with both antihistamine and mast cell stabilizing properties is a better choice than a preparation containing a vasoconstrictor. Full efficacy of prophylactic therapy with these agents can be assessed after at least two weeks of therapy.
These agents have two main actions:
 As mast cell stabilizers, they inhibit mast cell degranulation, which is the first step in the allergic cascade. They also inhibit leukocyte activity and dampen mediator release from mast cells, basophils, eosinophils, and neutrophils [20].
 As antihistamines, they competitively and reversibly block histamine receptors in the conjunctiva and eyelids, thus blocking the actions of the primary mast cell-derived mediator [21]. This also helps reduce the late phase of the allergic response.
Olopatadine was the first drug to receive approval as a combination antihistamine and mast cell stabilizer. It has been shown in vitro to inhibit histamine, tryptase, and PGD2 release from mast cells [22]. The H1-receptor selectivity is superior to that of other antihistamines [23]. Common side effects include stinging upon instillation and headache.
Other agents in this class include, but are not limited to alcaftadine (Lastacaft), azelastine HCl (Optivar), nedocromil (Alocril), epinastine (Elestat), pemirolast potassium (Alamast), and ketotifen fumarate (generic, Ketotifen), and bepotastine (Bepreve). Ketotifen fumarate is available in a generic formulation and is over-the-counter, as mentioned previously. Dosing is twice per day, except for Pataday and Lastacaft, which are dosed once daily.

- Seasonal and perennial allergic conjunctivitis — Treatment should be initiated at least two to four weeks before the onset of symptoms whenever possible to optimize effectiveness.
Preferred agents — Topical antihistamines with mast cell stabilizing properties (eg, olopatadine (Patanol, Pataday), azelastine HCl (Optivar), epinastine(Elestat), pemirolast potassium (Alamast), and ketotifen fumarate (generic, Ketotifen)) are the drugs of choice in treating SAC and PAC, since they address both the acute and more chronic aspects of these conditions. These medications were discussed previously. (See 'Frequent episodes' above.)
Other agents — Other useful agents include topical mast cell stabilizers and oral antihistamines. However, each of these options presents some limitations compared to combination topical mast cell stabilizer/antihistamine medications, as reviewed below:
 Mast cell stabilizers - Available agents include cromolyn sodium (generic, Opticrom) and lodoxamide tromethamine (Alomide). The onset of action is 5 to 14 days after therapy has been initiated, and therefore these medicines are NOT useful for acute symptoms [24]. In addition, dosing of mast cell stabilizers is four times daily, compared to twice daily for most agents with combined actions. These features may limit patient compliance.
 Nonsedating oral antihistamines - Nonsedating oral antihistamines include fexofenadine (generic, Allegra), loratadine (generic, Claritin),desloratadine (Clarinex), cetirizine (Zyrtec), and levocetirizine (Xyzal).
As mentioned previously, oral antihistamine use may be associated with drying of mucosal membranes and decreased tear production in some patients [30], especially those with concomitant dry eye [30]. This side effect can usually be countered with the liberal application of artificial tears. Cetirizine causes sedation in a subset of patients, despite its categorization as nonsedating.
Oral loratadine and fexofenadine were less effective than topical olopatadine in randomized trials [31,32]. Similarly, oral desloratadine was less effective than topical ketotifen [33].
 Nonsteroidal antiinflammatory drugs - NSAIDs block the action of cyclooxygenase and thus inhibit the conversion of arachidonic acid to prostaglandins and thromboxanes. In practical terms, however, NSAIDs are not considered to be as effective as other medical therapy in treating allergic ocular disease. As an example, ketorolac tromethamine was more effective than placebo in reducing the symptoms of acute allergic conjunctivitis [34]. However, it was less effective than olopatadine or emedastine [35,36]. Thus, NSAIDs are not recommended for the treatment of allergic conjunctivitis.

- Patients with concomitant rhinitis — In patients with concomitant allergic rhinitis, a topical agent that has both mast cell stabilizing and antihistamine properties can be combined with either an intranasal glucocorticoid or an oral antihistamine.

- Refractory symptoms — A minority of patients will not achieve control of their allergic conjunctivitis despite the above therapies.

- Ophthalmology referral — Referral to an ophthalmologist is highly recommended for patients who do not respond to two or three weeks of consistent therapy with an antihistamine/mast cell stabilizer agent.
Topical glucocorticoid preparations may be considered in patients with refractory symptoms.