In 1906, Von Pirquet¹ used the word “allergy” to describe this state of altered reactivity. The term atopy was coined by Coca and Cooke² to denote a wheal-and-flare skin reaction to antigen challenge in an individual with a history of allergy. Prausnitz and Kustner³ were the first to describe a wheal-and-flare reaction to an intracutaneous injection of fish extract in a person sensitive to the antigen. They also demonstrated that the reactivity may be transferred to the skin of a nonsensitized person by injection of serum from sensitized individuals (Prausnitz-Kustner reaction). The transferable serum component was called reagin. Later research revealed the component present in the serum reagin to be a new class of immunoglobulin, called immunoglobulin E (IgE) by the World Health Organization (WHO). In present day clinical practice, the term allergy refers to an acquired hypersensitivity and hyperreactivity to a foreign substance (allergen) resulting in damage to host tissues.

The symptoms that we currently attribute to ocular and nasal allergies following exposure to plant products were first described by Blackley in 1873.⁴ Peshkin used the allergen challenge model, also called conjunctival provocation testing (CPT), in conjunction with skin tests to diagnose ocular allergy.⁵ The model was also used by Abram⁶ and Tuft,^7,8 especially in cases in which skin tests were inconclusive. In research settings, the allergen challenge test allows a reproduction of the allergic response in a controlled environment. It has been used to establish cytokine profiles at various stages in the allergic reaction⁹ and to evaluate the efficacy of specific therapeutic interventions.¹⁰

The exact incidence and prevalence figures for allergic disorders are unknown due to considerable under-reporting. Skin test surveys suggest that as many as 40 to 50 million people in the United States suffer from allergies.¹¹ It is estimated that up to 22% of the population suffers from allergic eye disease,¹² and the percentage continues to rise.¹³

The economic burden created by ocular allergic disorder is increasing with the increasing cost of health care. It is estimated that the medical costs are between $1.5 and $2 billion annually in the United States alone. Aside from the monetary costs, these disorders significantly affect the quality of life of the affected patients.¹⁴

Allergic eye diseases are generally classified into four types:

Atopic keratoconjunctivitis (AKC) is a chronic inflammatory condition of the eye occurring in patients with a history of atopic dermatitis. It involves predominantly the lower tarsal conjunctiva. The symptoms frequently are disabling, and corneal involvement may lead to blindness. Ninety-five percent of the patients have a personal or family history of atopic disorders such as dermatitis, eczema, or asthma. However, only 25% to 42% of patients with atopic dermatitis develop ocular disorders.^12,43 In 1953, Hogan was the first to recognize the association of atopic dermatitis and ocular surface disorders.⁴⁴ The common ectodermal origin of the skin and ocular structure and their close proximity explain this association.

AKC usually presents from the late teens to the second decade, many years after the initial presentation of atopic symptoms. In many patients, the manifestations of disease improve with age and may completely disappear. Severe cases, however, do persist in to later life. Older patients tend to have the more severe form of the disease, which has its peak incidence in the 30-to 50-year-old age group. Males are affected more often than are females.