Allergies

Understanding Allergies and the Eye
Because the eye is an exposed moist area on the body, foreign particles such as pollen, cat dander and mold spores can adhere to the ocular surface and cause the same types of allergic reactions as these noxious substances generate in our nose, throat and lungs. Ophthalmologists are trained to recognize and treat ocular allergies and ocular effects of systemic allergies. It is no longer true that patients must simply suffer with their allergies and it is a mistake to believe that allergies are harmless, temporary annoyances.

The Biochemical Basis of Allergy
Allergy-causing materials, or allergens, do not initially cause overt responses. Instead, they first sensitize the body to their presence. This complicated biochemical pathway involves a number of different cells of the immune system. The normal job of these immune cells is to find foreign proteins, like bacteria, and not only kill them but also set up a system so that in the event the same type of protein is encountered, the body can act even more quickly to kill the germs, often without a patient knowing he suffered a repeat infection. If these foreign proteins are not bacteria (or some other micro-organism) but instead some common other substance, such as pollen, the body will still attempt to attack the substance. And since these substances are so common, the body develops a chronic state of readiness to fight the substances, i.e., an allergy. Once the allergic process is in place, an allergen acts as a trigger that begins a cascade of events, ultimately leading to either localized or systemic inflammation. It does this by interacting with a cell called the mast cell. This cell carries a protein on its surface called IgE. As the allergen contacts the IgE, the mast cells release a number of substances, many of which are inflammatory, the best known being histamine. When released around the eyes, histamine initiates itching, swelling, burning, redness and tearing, and also causes dry eye by making the tear-producing cells sick.

Nonmedical Therapy for Allergies
The best way to protect the eye from allergies is to avoid allergens altogether. It is useful to try to determine the substances provoking allergies and there are medical specialists called allergists who can provide a comprehensive battery of tests to help patients learn their particular triggers. Cigarette smoke, smog, petroleum solvents, fur bearing animals such as cats and horses, and certain house plants all produce irritating airborne substances that can often be avoided. Spectacles and facial hair should be cleaned frequently because they attract allergens and constantly present them to a patient. In addition, households can have air filters installed that effectively reduce allergens. When patients are outside, face masks can often help provide some relief.

Medical Therapy for Allergies
Topical medical therapies for ocular allergies take three approaches. The first is a preventive approach, where the medication either blocks the IgE on the mast cells, protecting it from the allergen, or the medication stabilizes the mast cell, preventing it from releasing its contents despite being stimulated. These medications take days to become effective and may not be the best way to handle an acute attack. The second group of medicines blocks histamine receptors on inflammatory cells, preventing their activity. Antihistamines are effective in acute disease, but are shorter lasting than preventive medications and can be associated with a rebound phenomenon, where the cessation of medication leads to particularly bad allergic symptoms. This causes some patients to become "hooked" on these medications during their allergy season. Finally, the third class of medications are anti-inflammatory drugs, that work at later stages in the inflammation cascade. These cells inhibit the inflammation producing cells from reacting even after they are stimulated. Drugs like aspirin, ibuprofen and steroids fall within this class. Topical anti-inflammatory drugs can be extremely useful in the short term, providing rapid and near complete relief. However, they can have serious side effects when used long term, such as causing the development of cataracts or glaucoma, and their use must be monitored closely by an ophthalmologist.

Consequences of Untreated Allergies
Most people would like to think of allergies as benign seasonal inflammations that cause some discomfort and then disappear for another year. This is far from true! Every time the eye is inflamed, it never completely recovers. Every bout of allergy raises the risk that a chronic dry eye condition may develop. And the swelling of the eyelids will eventually decrease their elasticity, predisposing the patient to malpositioned lids, such as ectropion or entropion. The inflammatory response on the underside of the eyelids causes bumps called papillae. These can swell to occlude the eye, and in patients under 9 years of age, cause amblyopia. In addition, these can cause sterile corneal ulcers that ultimately lead to corneal scarring and reduced vision. Ophthalmologists believe that the relief of patient suffering and the prevention of long term sequella are paramount when treating ocular allergies.