Mitchell H. Friedlaender

Disclosures

Curr Opin Allergy Clin Immunol. 2011;11(5):477-482. 

In This Article

Types of Ocular allergy

There are numerous classifications of ocular allergy, and it seems prudent to select one which takes into consideration our current understanding of immunologic mechanisms and their relationship to systemic disease. The simple classification below distinguishes between IgE-mediated and cell-mediated conditions. It also includes one disease, giant papillary conjunctivitis, which has certain signs suggestive of allergy, but is probably a strictly irritative phenomenon.

Seasonal and Perennial Allergic Conjunctivitis

Seasonal allergic conjunctivitis (SAC) and perennial allergic conjunctivitis (PAC) are the most common forms of ocular allergy (Fig. 1). Estimates vary, but these types of allergy are said to affect at least 15–20% of the population.[2] Signs and symptoms of these two conditions are the same. The difference is the specific allergens to which the patient is allergic. SAC is usually caused by airborne pollens. Signs and symptoms usually occur in the spring and summer, and generally abate during the winter months. PAC can occur throughout the year with exposure to perennial allergens. Diagnostic features of SAC and PAC consist of itching, redness, and swelling of the conjunctiva. Redness, or conjunctival injection, tends to be mild to moderate. Conjunctival swelling, or chemosis, tends to be moderate, and somewhat more prominent than one would expect for a mild amount of redness. Itching is a fairly consistent symptom of SAC and PAC. It is sometimes said that 'if it itches, it must be allergy, and if does not itch, it cannot be allergy'. This is probably an overstatement. Itching may, in fact, be associated with blepharitis, dry eye, and infection. Still, patients who complain of itching should be considered likely candidates for ocular allergy.

Figure 1.

Mild conjunctival redness (injection) and moderate swelling (chemosis) typical of acute seasonal and perennial allergic conjunctivitis

Vernal keratoconjunctivitis

Vernal keratoconjunctivitis (VKC) is a disease of warm climates and warm weather months.[3,4] It is more common in the tropics than in northern climes. However, it is not unusual to see occasional vernal conjunctivitis patients throughout the United States and Canada. Young people are typically affected. VKC may begin before puberty, and it usually resolves by age 20 years.[5] Patients often have a strong history of allergy to pollens, or other types of allergic conditions, such as atopic dermatitis, allergic rhinitis, or asthma. Symptoms include ocular itching, redness, swelling and discharge. Itching may be quite severe, and even incapacitating. Patients are often photophobic, sometimes intensely so. The most characteristic sign is giant papillae on the upper tarsal conjunctiva (Fig. 2). These 'cobblestone-like' swellings may be several millimeters in diameter. Usually, 10–20 are found on the tarsal conjunctiva, and they can be seen easily by 'flipping' the upper eyelid. There may be a tenacious mucous discharge between the giant papillae. As one might expect, the giant papillae are filled with inflammatory cells and edema. Neutrophils, plasma cells, mononuclear cells, and eosinophils are found in abundance. There is also a great deal of mast cell activity within the giant papillae. Mast cells can be seen in various stages of degranulation throughout the conjunctival stroma. Mast cells may also be found in the conjunctival epithelium, a location in which they are not normally present. The tears of VKC patients contain high levels of IgE and mast cell mediators.[6,7] Histamine, leukotrienes, prostaglandins, and kinase may be found in the tears of VKC patients.

Figure 2.

Giant papillae of the upper tarsal conjunctiva in vernal keratoconjunctivitis

The cornea may be affected in VKC. A punctate keratitis, known as keratitis epithelialis vernalis of El Tobgy, may begin in the central corneal. The dots may coalesce to form a syncytial opacity. This often leads to a whitish or grayish plaque beneath the epithelium (Fig. 3). These vernal plaques may interfere with vision and lead to central scarring of the cornea. This is one of the few instances in which ocular allergy can be associated with visual morbidity. Plaques can be removed by superficial keratectomy, but they rarely resolve without surgical intervention. Histologically, plaques consist of mucin and epithelial cells which are literally ground into the central cornea. VKC patients may also demonstrate Trantas dots (Fig. 4), small white dots usually at the superior limbus. The dots represent almost pure collections of eosinophils.[5] These cells collect in crypts which are formed by invaginations at the junction of the cornea and conjunctiva. Trantas dots tend to appear when VKC is active, and disappear when symptoms abate.

Figure 3.

Corneal plaque in vernal conjunctivitis

Figure 4.

Trantas dots in vernal conjunctivitis

Atopic Keratoconjunctivitis

Atopic keratoconjunctivis (AKC) is the ocular counterpart of atopic dermatitis, or atopic eczema.[8•] Eczematous lesions may be found on the eyelids (Fig. 5), or any place on the body. Skin lesions are red and elevated. They often occur in the antecubital or popliteal regions. Typically, eczematous lesions are itchy, and scratching them makes them more itchy. Ocular findings vary. The eyelid skin may have a fine sandpaper-like texture. There may be mild, or severe, conjunctival injection and chemosis.[9] Giant papillae may, or may not, be present. Conjunctival scarring is common. Trantas dots may also be present. AKC is said to be associated with keratoconus. If this association exists, it is relatively uncommon. Most atopic patients do not have keratoconus, and most keratoconus patients do not have AKC. It has been suggested that eye rubbing, precipitated by ocular itching, may lead to keratoconus. Whereas this may be an interesting theory, there does not seem to be much evidence that rubbing the eye could create an ectatic corneal condition like keratoconus. AKC patients may also develop atopic cataracts (Fig. 6). Typically, these are anterior, shield-like cataracts, but nuclear, cortical and even posterior subcapsular cataracts may develop. Corticosteroid therapy of AKC may contribute to cataract development.[10] However, atopic cataracts were documented long before corticosteroids were available for medical use. It is not unusual for AKC patients to have cataract surgery at a young age.

Figure 5.

Atopic keratoconjunctivitis with eczematous skin lesions of the eyelids

Figure 6.

Anterior shield-like cataract associated with atopic keratoconjunctivitis

It may seem that the appearance of VKC and AKC is similar. Both may be associated with giant papillae and Trantas dots. In fact, there probably is some overlap between these two conditions. VKC, however, resolves by age 20 years, whereas AKC can persist throughout life.

Contact Allergy

Contact allergy, or contact dermatitis, is not an IgE-mediated allergy, and can be considered in a different category than the aforementioned allergic conditions.[11] Contact allergy is mediated by lymphocytes, rather than antibody. Allergens are generally simple chemicals, low molecular weight substances that combine with skin protein to form complete allergens. Examples include poison ivy, poison oak, neomycin, nickel, latex, atropine and its derivatives. Although contact allergic reactions usually occur on the skin, including the skin of the eyelids (Fig. 7), the conjunctiva may also support contact allergic reactions. Initial sensitization with a contact allergen may take several days. Upon re-exposure to the allergen, an indurated, erythematous reaction slowly develops. The reaction may peak 2–5 days after re-exposure. The delay in development of the reaction is due to the slow migration of lymphocytes to the antigen depot. The term 'delayed hypersensitivity' is sometimes given to these reactions, in contrast to 'immediate hypersensitivity', a term which emphasizes the rapid development of IgE antibody-mediated reactions. Contact allergic reactions are generally associated with itching. Treatment consists of withdrawing, and avoiding future contacts with the allergen. Patch testing is sometimes used to identify unknown allergens. Severe reactions can be treated with topical or systemic corticosteroids.

Figure 7.

Contact allergy to neomycin eyedrops

Giant Papillary Conjunctivitis

Giant papillary conjunctivitis (GPC) is not a true ocular allergy, but rather an irritant phenomenon (Fig. 8), which induces giant, medium, or small papillae in the superior palpebral conjunctiva. GPC used to be classified as an allergic phenomenon because of conjunctival changes similar in appearance to vernal conjunctivitis.[12] However, the incidence of systemic allergy in GPC patients is similar to that of the general population, and the stimuli for the papillary conjunctival changes are inert substances rather than allergens. For example, GPC may be caused by limbal sutures, contact lenses,[13] ocular prostheses, and limbal dermoids. When these irritative stimuli are removed, the conjunctival papillary changes resolve. The conjunctival tissues may contain mast cells, basophils, or eosinophils, but not to the extent of an allergic reaction. There is no increase in IgE or histaimine in the tears of GPC patients. Since the advent of disposable contact lenses, the frequency of GPC is low. It appears that protein build-up on the surface of contact lenses, and irregular edges were the main reason for the close association between contact lenses and GPC.

Figure 8.

Giant papillary conjunctivitis caused by contact lens wear

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