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Management of Ocular Allergies
Ocular allergy is a common condition affecting approximately 17 to 20% of the population, and its incidence is increasing.(1,2,3,4) The conjunctiva is exposed to many environmental allergens and is often the location of initial contact with an allergen. For this reason, the management of ocular allergies is a very important aspect of many vision care practices.
ALLERGIC CONJUNCTIVITIS AND KERATOCONJUNCTIVITIS
Allergic ocular surface disease is traditionally divided into five categories, all of which result from a hypersensitivity reaction by ocular tissues to one or more allergens.
Mild, acute allergies include:
Seasonal allergic conjunctivitis (SAC), and
Perennial allergic conjunctivitis (PAC).
Chronic allergic diseases with the potential for causing significant ocular consequences include:
Giant papillary conjunctivitis (GPC),
Atopic keratoconjunctivitis (AKC), and
Vernal keratoconjunctivitis (VKC).
Atopic and vernal keratoconjunctivitis are potentially vision-threatening conditions due to the risk of corneal ulceration, vascularization, and scarring.(4)
Seasonal and perennial allergic conjunctivitis
Although SAC (also known as hay fever conjunctivitis) is less severe than other ocular allergies, it is by far the most common type of allergy affecting the eyes.(5,6) SAC typically occurs in the fall and spring when grass, tree, or ragweed pollens are abundant. In contrast, PAC can occur year round, and its causes can include animal dander, insects, and dust mites.
Age of onset
SAC and PAC can occur at any age, but patients are typically young, with an average age of 20 to 30 years.(5,6,9) The incidence of sensitivity to airborne allergens typically begins around age 8 to 10 years of age.(10) Eighty percent of people who will develop allergies have symptoms before the age of 20 years.(11) There is no statistical difference in the number of females versus males affected by seasonal and perennial allergies.(8,9,12) One recent study found a relationship between increased myopia and the prevalence of ocular allergies.(79)
Cost of ocular allergies
SAC and PAC do not typically threaten vision, but they do alter the quality of life, cause missed workdays, and inflict a significant social and financial burden on patients.(7)
Ocular allergy symptoms can result in patient discomfort that interferes with visual tasks such as computer work and recreational activities. Twenty percent of allergy suffers report taking time away from work due to allergy symptoms.(8) Direct and indirect costs of SAC and PAC include lost wages as well as physician and medication costs.(7)
Exposure to environmental allergens, such as cigarette smoke and pollution, has been associated with the development of ocular allergies to other allergens.(10) Children born by Caesarean section (13) and those who were fed milk other than breast milk during the first 4 months of life (10) also have an increased risk of developing allergies. Dietary intake of n-6 polyunsaturated fatty acids has also been associated with seasonal rhinoconjunctivitis.(14)
Vernal keratoconjunctivitis is rarer than SAC and PAC, but due to possible corneal involvement, it is potentially a more serious condition. VKC has a mean age of onset of 7 years and the majority of cases (85%) have an onset prior to age 10 years.(16) For this reason, an initial diagnosis of VKC in an adult patient should be suspect.(5)
VKC is found most commonly in males (6,15) and is most likely to occur in warm, windy climates such as the Mediterranean, West Africa, Japan, India, and South America.(17,18) The condition is not as common in North America and Western Europe (17); however, the migratory nature of populations accounts for an increased prevalence of the disease in these countries.(18)
Atopic keratoconjunctivitis, which is an allergic conjunctivitis associated with atopic dermatitis, is the most potentially blinding of all of the ocular allergies.(1) Like vernal, AKC is more common in males. The condition typically begins in the late teens or early twenties with a peak severity occurring between ages 30 to 50 years.(19) Patients with AKC typically have eczema on the eyelids and skin as well as a history of asthma.
Approximately 15 to 40% of patients with atopic dermatitis will develop AKC,(17) and at least 95% of patients with AKC have eczema.(19) Eczema typically starts in childhood, and ocular symptoms occur somewhat later in life.(20)
Giant papillary conjunctivitis
With the use of disposable contact lenses, GPC has become a far less frequently occurring allergy. However, the condition does continue to affect some contact lens wearers.(80) GPC most commonly develops after prolonged conjunctival contact with a foreign substance such as a contact lens. It has also been reported with exposure to ocular sutures or prostheses.
Often it is not the contact lens itself that causes GPC, but rather it is deposits or allergens on the surface of the contact lens. These allergens are rubbed against the upper palpebral conjunctiva many times during the day, and this causes sensitization.
GPC can occur in patients who wear either hard or soft contact lenses, but soft lenses cause GPC more commonly than rigid contact lenses. This is due to the ability of soft contact lenses to accumulate more deposits than rigid lenses. Also, the larger surface area of a soft lens produces a larger area of reaction. People who sleep in their lenses are three times as likely to develop GPC as those who do not.
REVIEW OF IMMUNOLOGY
Patients typically consider ocular problems; including itch, watering, and redness; to be the most important symptoms requiring relief.(21) However, these symptoms are often overlooked by non-eye care practitioners, and many physicians minimize the effects that allergies have on their patient’s comfort and wellbeing.(22) Because of this, a large number of patients self-medicate to reduce their symptoms, and, as a result, many of them are not treated fully or appropriately. An understanding of basic immunology will aid in proper diagnosis and appropriate management of patients with ocular allergies.
Mast cells are primarily responsible for the hypersensitivity reaction that occurs in SAC and PAC. In addition to mast cells, eosinophils and T lymphocytes are also involved in VKC, AKC, and GPC.
Allergy symptoms occur after an allergen binds to immunoglobulin E (IgE) on conjunctival mast cells in a sensitized individual. This causes mast cell degranulation, which releases inflammatory mediators such as histamine, leukotrienes, prostaglandins, tryptase, and cytokines.(23,24) These mediators trigger the acute, or early phase, of an allergic reaction. Histamine induces itching, redness, and swelling. Prostaglandins and leukotrienes are responsible for increased mucus secretion and vascular permeability.
Large doses of an antigen can cause the initial allergic reaction to progress to a late-phase response.(25) Eosinophils and T lymphocytes are responsible for this late-phase reaction. T helper 2 (TH2) cytokines, including interleukin (IL)-4, IL-5, IL-6, IL-8, IL-13, stem cell factor, platelet activating factor, and tumor necrosis factor (TNF) can trigger a series of inflammatory events.
These events, including the expression of chemokines, protein regulated on activation normal T-cell expressed and secreted (RANTES) monocyte chemoattractant protein-1 (MCP-1), eotaxin, intercellular adhesion molecule (ICAM-1), vascular cell adhesion molecule (VCAM), and p-selectin lead to the recruitment of eosinophils and neutrophils. This can result in allergy symptoms that persist for up to 24 hours.(23,26)