Exposure to cats and cockroaches may increase the risk for glaucoma, but contact with dogs could guard against the common eye disease, suggests a study in the American Journal of Ophthalmology.

People with glaucoma had significantly higher levels of immunoglobulin E (IgE), a type of allergic antibody, to cats and cockroaches, compared with people without glaucoma, the study found. Levels of IgE are elevated in various immunological disorders, such as asthma and hay fever, raising the possibility the immune system plays a role in glaucoma, the researchers said. Elevated IgE doesn’t mean a person has an allergy.

Researchers at the University of California, Los Angeles, analyzed data from 1,678 people enrolled in a larger study. The subjects, who were in their 50s and 60s, underwent allergy testing for dust mites, cats, dogs, cockroaches and rodents. Use of steroids, which are linked to glaucoma, was recorded.

Glaucoma was diagnosed in 5.1% of the subjects. Of these, 14.3% had significantly elevated IgE levels to cats and 19.1% to cockroaches. In contrast, 10% of the nonglaucoma subjects had elevated IgE for either cats or cockroaches. Levels of IgE to dog allergens were elevated in 6% of glaucoma patients and in 9.2% without glaucoma.

Total IgE levels for all of the tested allergens weren’t associated with glaucoma, suggesting it is specifically the cat and cockroach allergens that are associated with the development of glaucoma, researchers said.

Allergens from cats and cockroaches may have biochemical or physical properties that trigger antibodies targeting the optic nerve, while dog allergens may behave differently, possibly because dogs spend more time outdoors, the study suggests.

An estimated 27 million Americans have glaucoma, a group of eye diseases caused by progressive optic-nerve damage, according to the National Eye Institute.

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