Optimizing the Treatment of Ocular Allergy
Optimizing the Treatment of Ocular Allergy
Not every reaction to ragweed or pet dander is allergic in nature, so the first step in treatment is determining the cause of the reaction.
By Robert Lanier, MD
While patients use the term “allergy” quite broadly, not all adverse reactions to food, pet hair, or pollen are the result of a true allergic response. Strictly defined, allergy is a dynamic, active immune defense against a protein, typically associated with the allergic antibody immunoglobulin E (IgE). While other hypersensitivities may produce similar symptoms, they often result from a chemical reaction or other non-immune mechanism.
Because the underlying disease process determines which treatments will be effective, clinicians need to evaluate patients carefully to distinguish between true allergy and other conditions. Antihistamines are generally very effective for allergic conjunctivitis, but they will provide little benefit for non-allergic conditions. In addition, patient education plays a large role in effective allergy treatment, since patients can often achieve a significant reduction in symptoms simply by learning to avoid the substances that trigger their allergies.
Allergy in the US
In the past, regional variations in plant and animal species produced different allergy patterns across the country. Differences in soil acidity, weather, and other geographic factors allowed certain plants to grow only in the Eastern or Western United States, and the Rocky Mountains served as a physical barrier to limit the spread of pollen beyond the plants’ native ranges. With the advent of interstate highways, railroads, and other transportation links, however, massive flows of people and commerce have redistributed our nation’s fauna and flora, and today we see much more homogeneous pollen sensitivities across the country. Differences in temperature still affect when local plants produce pollen and for how long, but the allergens themselves tend to be widely distributed.
For patients, this means that moving to a different part of the country is unlikely to alleviate their allergy symptoms over the long term, although it may give temporary relief. In addition to the fact that no region of the country is allergen-free, we also know that patients with allergies have a genetic predisposition to develop hypersensitivities to innocuous proteins. Thus, even when they move to an area where the local pollen does not affect them, allergic patients are likely to develop sensitivities to new allergens within a few years.
Interestingly, while the genetic trait that causes patients to develop allergies seems maladaptive, it may have some benefits. For example, people with allergy and asthma tend to live longer than people who do not have allergies, and they tend to have fewer forms of cancer.
Clinical Presentation and Diagnosis
Thought to have developed as an evolutionary defense against parasites, allergy causes the release of histamine, which leads to a number of effects (which, unfortunately, patients perceive as symptoms). In the eye, allergy causes itching, redness, and tearing; in the nose, it triggers nasal discharge and sneezing. Allergy can also affect the lungs and skin causing asthma and eczema, respectively.
When patients exhibit ocular symptoms in the context of rhinitis or other signs of allergy, the diagnosis of allergic conjunctivitis is usually clear. If patients have only ocular symptoms, however, allergy may be misdiagnosed. Patients with dry eye disease or other non-allergic ocular surface conditions are also frequently misdiagnosed as having allergy, even though the cause of their symptoms is quite different.
While there are always exceptions, the general rule for diagnosing allergy is that if patients describe itching, then they have allergic conjunctivitis, but if they report burning, then the condition is usually not allergic. In some cases, a trial of antihistamine therapy can help to distinguish allergy from other conditions, since antihistamines are usually very effective at alleviating allergy symptoms but provide minimal benefit for non-allergic conditions.
In addition to distinguishing allergy from non-allergic disease, clinicians should consider whether the patient has seasonal or perennial allergies. Typically, seasonal allergies involve a response to one or more types of pollen that are present only during certain times of the year. On the other hand, perennial allergies result from sensitivities to allergens that are present year-round—such as house dust, animal feces, or indoor molds—making this a chronic condition that tends to be more difficult to treat.
Medical Treatment Options
Because histamine release is central to the allergic response, topical antihistamines are usually a very effective treatment for allergic conjunctivitis. With drugs such as Patanol® (Alcon), Pataday™ (Alcon), Elestat® (Allergan), and Bepreve™ (ISTA Pharmaceuticals), clinicians currently have a number of options from which to choose. When selecting one of these medications, clinicians should consider the comfort of the drop and the dosing frequency, as both factors can significantly affect patient compliance. If cost is an issue, ketotifen is now available in over-the-counter formulations, including Alaway® (Bausch & Lomb) and Zaditor® (Novartis).
In addition to antihistamines, mast cell stabilizers and steroids can also play a role in the treatment of allergic conjunctivitis. Like antihistamines, mast cell stabilizers target histamine, but they do so by preventing histamine release rather than blocking the histamine receptors. Many of the medications listed above have mast cell stabilizing properties in addition to their antihistaminic effects.
Steroids do not act on histamine, but they can be used to quiet the eye in allergic conjunctivitis patients who have significant ocular surface inflammation. Because of the risk of intraocular pressure spikes and cataract formation, allergists like myself are often hesitant to prescribe topical steroids, especially for long-term use, so these patients are often referred to an ophthalmologist or optometrist for treatment and monitoring.
Finally, patients who have both ocular and non-ocular symptoms may require a nasal or systemic antihistamine. An important caveat when using such drugs is that they can sometimes be drying to the eye, which may exacerbate the patient’s ocular discomfort. Thus, while a systemic antihistamine or a high dose of nasal antihistamine may relieve both ocular and nasal symptoms, this is not always the best treatment approach. Instead, patients with ocular symptoms are often better served by treatment that addresses the eye directly.
While topical antihistamines are a very effective treatment for allergic conjunctivitis, environmental modification is also important. If patients know what triggers their allergies and learn how to avoid these substances, they can often significantly reduce the severity of their symptoms. I therefore encourage patients to take practical steps to reduce their exposure to common allergens—for example, by encasing their mattress in a dust mite cover or washing their hair to remove pollen before going to bed.
One of the most common triggers of perennial allergies is house dust, which carries a large load of dust mite excrement. While some dust exposure is unavoidable, putting dust mite covers on mattresses can help to minimize patients’ exposure, since mattresses are one of the major reservoirs of dust mite excrement. Patients with perennial allergies should therefore replace their mattresses and/or find a way to seal up the mattress so that dust mites cannot get in and out. Linen mattress covers work well and are comfortable, but they can be fairly expensive; as an alternative, patients can encase a mattress in plastic and seal it with duct tape.
Another common allergic trigger is pollen. Again, some pollen exposure is unavoidable, but patients can minimize the severity of their allergy symptoms by washing their hair before bed. Because hair fibers carry an electrostatic charge, they attract pollen during the day; at night, the electrostatic charge drops, causing the pollen to fall off the hair fibers onto pillows and into patients’ eyes. If patients find it inconvenient to wash their hair in the evenings, an alternative is to use hair spray or mousse to keep the pollen from coming loose during the night and then wash their hair in the morning.
THE BOTTOM LINE
Common in all parts of the United States, allergies result from an immune response against various otherwise innocuous proteins, including those found in dust, pollen, animal dander, and mold. Because allergies can cause significant patient discomfort, proper diagnosis and effective treatment are essential. In addition to the use of medications—including antihistamines, mast cell stabilizers, and steroids—non-medical therapies can also help to relieve patients’ symptoms. Specifically, patients can benefit from fitting their mattress with a dust mite cover and washing pollen out of their hair before bed.
Robert Lanier, MD, is clinical professor of pediatrics and immunology at the University of North Texas Health Science Center in Fort Worth, TX.