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Allergic Disorders of the Eye

Virginia L. Calder, Amirah Mohd-Zaki, Valerie Saw

Allergic disorders of the eye range from the mild conditions of to open the lids and a ballooning out of the conjunctiva termed
seasonal and perennial allergic conjunctivitis (SAC, PAC), due chemosis, particularly after exposure to high aeroallergen con-
to immunoglobulin E (IgE)–mediated mast cell and histamine- centrations or after rubbing of the eye. Eversion of the lids to
related inflammation, to the clinically more severe diseases reveal the tarsal conjunctiva demonstrates some hyperemia and
associated with T cell–mediated chronic inflammation, vernal mild infiltration (loss of transparency and thickening) of the
and atopic keratoconjunctivitis (VKC, AKC). The ocular allergic conjunctiva with diffuse small inflammatory excrescences known
responses in SAC and PAC are confined to the conjunctival tissues, as papillae. Because there is no serious limbal disease or con-
whereas in both VKC and AKC the cornea also can become junctival scarring and the cornea is not involved, the visual acuity
involved, potentially leading to impaired vision. Research to remains normal. Outside the pollen season, the eye examination
identify the inflammatory cells and molecules involved in allergic is normal.
responses at the ocular surface and their role in the pathogenesis
of allergic eye diseases has increased in the past few years. Extensive Conjunctival Immunostaining in SAC
immunohistochemical studies have identified distinct expression SAC involves an immediate, rapid early-phase hypersensitivity
profiles of adhesion molecules, chemokine receptors, cytokines, response due to allergens binding and cross-linking IgE molecules
and immune cell types for each subtype of allergic conjunctivitis, attached to tissue mast cells. The acute response is rapid, usually
while immune pathways are being studied via novel experimental taking place within 30 min. The late-phase response occurs 6–12 h
models. This chapter reviews recent advances in our understanding after antigen exposure and involves the infiltration of inflam-
of the cellular and molecular processes occurring in ocular allergy. matory cells, primarily mast cells, and some eosinophils and
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neutrophils (Fig. 47.1). Primarily mast cells and their degranula-
tion products (histamine, proteases, leukotrienes, chemokines,
KEY CONCEPTS and cytokines) orchestrate the inflammatory response in SAC,
Predominating Cell Types in the although neutrophils and eosinophils also secrete a wide range
Conjunctival Tissues of proinflammatory mediators that amplify the inflammation.
Immunohistochemical studies of tarsal and bulbar conjunctival
In seasonal and perennial allergic conjunctivitis: mast cells biopsy specimens demonstrated increased expression of intercel-
In vernal keratoconjunctivitis: eosinophils, T cells, neutrophils, mast cells lular adhesion molecule (ICAM)-1 and E-selectin adhesion
In atopic keratoconjunctivitis: T cells, eosinophils, neutrophils molecules in SAC in comparison with controls, but only inseason,
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and expression returns to baseline outside the pollen season.
This pattern of expression is correlated with the degree of
SEASONAL ALLERGIC CONJUNCTIVITIS neutrophil or eosinophil infiltration in the bulbar tissue, sug-
gesting a mast-cell–mediated cell recruitment process.
Ocular allergy, principally SAC, is the commonest ocular disorder
seen in primary care. SAC is a recurrent conjunctivitis apparent Therapy
only during the pollen season; the timing (spring, summer, or General measures may provide effective relief, particularly when
autumn) is dependent on which particular pollen or mold is the disease is not severe. Limiting pollen exposure by keeping
allergenic for that individual. The disorder can occur at any age windows shut and remaining indoors, especially on high-pollen-
but is more frequently seen in children and young adults and count days, is common sense. Cold compresses and ocular
tends to lessen in severity in the older age groups. lubricants (artificial tears) relieve symptoms, particularly itching.
Patients present with seasonally recurring itching, watering, Numerous classes of agents, both systemic and topical, have
redness, and swelling of the eyes and lids, and there may be been used to manage the signs and symptoms of allergic con-
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increased conjunctival discharge. An associated rhinitis is junctivitis. Topical mast cell inhibitors, the prototype being
common. A personal or family history of atopy very often can sodium cromoglycate, are the most useful drugs for non-sight-
be elicited. During the allergen season, the ocular signs range threatening ocular allergy. Sodium cromoglycate eye drops are
from mild to dramatic and are usually bilateral and symmetrical. available over the counter. They have a number of effects
Edema of the lids and conjunctiva may be mild and often (inhibition of other leukocytes, direct mediator antagonism) in
outweighs the degree of hyperemia, giving a milky or pink addition to inhibiting mast cell degranulation (one of the earliest
appearance to the eye, but the swelling may be gross, with inability mechanisms of the acute ocular allergic response), which accounts

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