Flat collars and eye pressure: the forgotten argument in the collar-versus-harness debate
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
The collar-or-harness debate usually revolves around the windpipe, the neck vertebrae and general comfort. A third organ is involved and hardly ever comes up: the eye. Pauli, Bentley, Diehl and Miller measured it first, in 2006 in the Journal of the American Animal Hospital Association, across 51 eyes from 26 dogs: applying to the neck the force a dog generates when pulling against its collar significantly raises intraocular pressure, whereas the same force applied through a harness does not (see the study). Our equipment guides sit in the dog accessories section.
Contents · 5 sections
A recent replication, this time while walking
The 2006 work used simulated pressures during tonometry, not a dog actually walking. Bailey, Packer and Wills reran the experiment under walking conditions and published in 2025 in Veterinary Medicine and Science, with 24 healthy dogs split into brachycephalic and dolichocephalic groups (see the study). Three findings stand out. Simply wearing the collar while standing still raised pressure in the flat-faced dogs, but not in the long-muzzled ones. Walking on the collar raised it in both groups. Walking on the harness raised it in neither.
The striking number is not an eye pressure
It is the pressure applied to neck tissue. The lowest value recorded under a collar in that study reached 83 kPa, while human work places the threshold for tissue damage from sustained compression at around 4.3 kPa. The order of magnitude leaves little room for interpretation, even allowing for the dog's thicker skin and the brief nature of a pull.
What these studies do not say
Neither shows that a collar causes glaucoma, optic nerve damage or vision loss: they measure a transient rise in pressure, not a long-term clinical consequence. The 2025 sample is modest, with a single operator and moderate walking rather than genuine lead-pulling. Nothing covers wide padded collars either. One detail matters for owners of flat-faced dogs: in that same study, respiration rate rose as much on the harness as on the collar during exercise. A harness protects the eye; it does not fix the breathing.
Who this actually changes things for
For a healthy dog walking on a loose lead, the issue stays theoretical. It becomes concrete for three profiles: dogs with diagnosed or monitored glaucoma, predisposed breeds such as the one covered in our guide to primary glaucoma in the basset hound, and dogs that have had eye surgery or have a fragile cornea. For them, a dog that genuinely pulls stacks up several avoidable pressure spikes per walk. The general comparison of the two options is covered in our harness or collar guide, and the specific case of small breeds with a fragile windpipe in the one on tracheal collapse in the Pomeranian.
- 51 eyes, 26 dogs: pressure rises under a collar, not under a harness (Pauli 2006).
- Walking on a collar: intraocular pressure rose in both head shapes tested in 2025.
- 83 kPa: the lowest pressure measured under a collar, against 4.3 kPa as the human tissue-damage threshold.
- No study links collar use to diagnosed glaucoma.
Frequently asked questions
Should every dog give up the collar?
No. The data concern pulling, and apply first to dogs at ocular risk. A collar remains useful as an ID tag holder and for a dog that does not pull.
Does a harness also fix breathlessness in flat-faced dogs?
No: in the 2025 study, respiration rate during exercise rose as much with one as with the other. The cause is anatomy, not equipment.
Does a padded collar make a difference?
No published data allow that claim: both studies tested conventional flat collars.
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This guide is part of Planète Pets’s Dogs universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.