It may seem difficult to believe that pet ownership has anything to do with vision, but new research suggests a possible link. A study conducted by the University of California, Los Angeles, revealed that cat owners who reacted to their cat’s allergen had a 90 percent increased risk of glaucoma compared with non-cat owners. Meanwhile, dog owners were 20 percent less likely to develop the debilitating condition.
“The goal of the study was to assess whether there were any associations between increased sensitivity to a panel of common indoor allergens and glaucoma risk,” says Anne L. Coleman, MD, PhD, and head of the study. “Specifically, we wanted to see if people who had elevated levels of serum antibodies to dust, cat dander, dog dander, cockroaches, mice or rats had an increased risk of glaucoma.”
The Search Begins For A Link Between Pet Allergens And Glaucoma
The researchers chose this topic because previous studies had demonstrated that sensitization to indoor allergens can be associated with asthma, which is a chronic lung condition, and they thought it would be interesting to investigate whether there are similar associations with glaucoma — a chronic eye condition.
Glaucoma occurs when fluid in the eyeball stops draining efficiently, causing a build-up of pressure, which damages the optic nerve and nerve fibers from the retina. Previous studies have suggested that inflammation can drive the disease, and the researchers wanted to find out if that could be triggered by pet allergens.
How The Research Was Done
The study was conducted based on the 2005-2006 National Health and Nutrition Examination Survey (NHANES) population. The NHANES study examines a representative sample of adults and children throughout the United States and uses data from this sample to produce weighted estimates that are meant to be representative of the U.S. population.
“Our study included 1,678 adults in NHANES over age 40, which led to a weighted estimate of 83,308,318 individuals,” Coleman says.
To measure sensitivity to indoor allergens, participants had their blood drawn and their blood samples were tested against antigens from dust, cat dander, dog dander, cockroaches, mice and rats. Immunoglobulin E (IgE) antibody levels to these antigens were then measured in each blood sample to determine if participants had levels that were above normal.
Animals frequently groom themselves, so allergens from saliva and secretions spread throughout the home, becoming airborne easily — where humans can inhale them. When humans suffer an allergic reaction to animals, their levels of IgE antibody rises, which causes itchy eyes, sneezing and congestion.
“Each participant had optic nerve photos taken and also performed a visual field test, which can show patterns of vision loss that are suggestive of glaucoma,” Coleman says. “Based on the photos and the visual field test results, we used a standardized protocol to determine if participants were likely to have glaucoma.”
The Study Indicates A Need For More Research
Scientists had already discovered that dogs and cats carry antigens, which can prompt different immune responses in humans. This study found that, while the allergen that dogs carry reduces the chance of developing glaucoma — the second leading cause of blindness — owning a cat nearly doubles the risk of contracting the eye disease for those who have allergies to cats.
“This does not in any way prove that allergies to cats or dogs can cause or prevent glaucoma; it just suggests that there may be common mechanisms relating sensitization to cat and dog antigens and glaucoma,” Coleman says. “Our study suggests the need for further clinical and laboratory studies specifically examining the scientific mechanisms behind allergies and glaucoma to see if there is a potential link between the two conditions. At this point in time, we would not suggest that any pet owners make any changes based on the findings from our study.”
Health Benefits From Dogs
Keeping a dog also has the added benefit that owners are outside more, which has been proven to protect against nearsightedness.
“The protective effect of dogs could be due to their natural antigens in their dead skin, but might also be because they spend more time outdoors and are happy to get dirty, whereas cats are cleaner animals,” Coleman says. “We already know that exposure to dogs and the germs and bacteria they carry can be good for the immune system. Now it seems to be the case for the eyes, too.”
Keeping Your Eyes Healthy
While some pet owners suffer mild allergic reactions to their pets and still choose to keep them, the new study suggests that even a small immune response could lead to blindness.
As several eye conditions are chronic and develop slowly over time, the researchers suggest that people visit their eye doctor on a regular basis for routine screening and early detection of any eye conditions that may exist.