The following is a blog post by our contributor and cat lover Alan Cassels, who turned to a physician-journal editor-cat lover for expert analysis.
A recent story in the Wall Street Journal stated that exposure to cats and cockroaches “may increase glaucoma risk” for people. This study, published in the American Journal of Ophthalmology also concluded that contact with dogs could guard against the common eye disease. Before writing off this story as another piece of propaganda peddled by the rabid anti-cat lobby, (whose motto is: “Felines make the best fiddle strings”) it’s worth taking a closer look at the actual study. The WSJ reported that 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.”
Elevated levels of IgE are found in various immunological disorders, such as asthma and hay fever, and the researchers hypothesized that the immune system probably plays a role in glaucoma.
The study looked at 1,678 people in their 50s and 60s, who all underwent allergy testing for dust mites, cats, dogs, cockroaches and rodents. About five percent of the subjects had glaucoma. 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.”
So what’s one to make from all this? The theory is that allergens from cats and cockroaches may trigger antibodies targeting the optic nerve. That sounds like a reasonable hypothesis but what about dogs? Why single out felines as the prime pet-suspect in glaucoma? Apparently because dogs spend more time outdoors, their allergens behave differently.
For some sober second thought on this study I sought out a fellow cat-lover who could give an appropriate critical appraisal of this study. Dr. Elizabeth Loder, a Boston-based research editor for The BMJ, is a cat owner (like myself) and (like myself) was admittedly well-primed to deliver a gentle smack-down to this study’s tenuous findings.
She told me over the phone from her office at the Brigham and Women’s Hospital in Boston that the link between cat allergens and the development of glaucoma was described in a way that “seemed very causally related,” but it also, in her mind, “seemed very unlikely to be true.” She took a closer look at the study and noted that the researchers were more cautious in their assessment of such a link than the journalist. If anything, she adds, “the study is hypothesis–generating.”
Even though there might be a weak biologic rationale (some literature suggests there’s an inflammatory response in glaucoma) Dr. Loder is not likely to get rid of her Siamese cat anytime soon. She was reassured by the confidence interval for the odds ratio which was “especially wide for the cat.”
I, too, was happy as she reassured myself and many cat-owners who read the Wall Street Journal that we should not start distrusting our choices of pet, fearing a glaucoma-filled future.
Clearly, as we’ve established previously, as in this earlier blog post, Cat People (you know who you are) already have blinders on, so they don’t need more data-dredging health stories like this one to make them suspicious of their cat. Especially when cats are so adorable, and otherwise incredibly good for your health, which this valiant bit of cuteness from the Huffington Post tried to establish.
Note to file: just to clear up a bit of misinformation from the anti-cat lobby, according to Wikipedia, “Catgut” does indeed make very good violin strings, but no actual cats are sacrificed in the interests of fine music. Catgut is made from the intestines of sheep and goats.
Another note: see some of the comments following the online WSJ story: