05/06/2026
A new peer-reviewed review published by researchers at the University of Illinois examined the health effects of common dog equipment, including collars, harnesses, leashes, and muzzles. One of the most surprising findings was that regular flat collars can increase intraocular pressure (IOP)—the pressure inside the eye—especially in flat-faced breeds such as Pugs, Bulldogs, and Boston Terriers. Harnesses did not show the same effect.
Elevated IOP is a major risk factor for glaucoma and other forms of eye damage, and repeated increases over time may place additional stress on delicate ocular structures.
The review also noted that many commonly repeated concerns about collar-related thyroid injury, tracheal damage, spinal problems, and even IOP have limited direct scientific evidence. Rather than disproving these concerns, the authors emphasized how little research has actually been conducted on equipment that millions of dogs wear every day.
This highlights an important reality in veterinary medicine: the absence of published research is not the same as evidence that a problem doesn’t exist. Many functional medicine and integrative veterinarians have spent decades observing patterns in clinical practice long before studies were available to investigate them. Those observations often become the very questions researchers study years later.
Science is essential, but science also has gaps. Some of the most important decisions we make for our animals happen in those gaps, where common sense, clinical experience, pattern recognition, and a commitment to minimizing harm matter deeply. Partnering with a veterinarian who understands both conventional medicine and a broad range of healing modalities can provide a wider lens through which to evaluate risk, support wellness, and potentially avoid problems long before they become scientifically validated. Sometimes the best medicine isn’t waiting for proof—it’s paying attention to what thoughtful clinicians have been seeing all along. Above all, do no harm.
