The Royal Veterinary College has published new research which has revealed the risk factors for Prolapsed Nictitating Membrane Gland, aka Cherry Eye, in dogs.

Led by the RVC’s VetCompass Programme, researchers say the study1 was the largest exploration of cherry eye in dogs in the world.

The research team followed the anonymised veterinary health records of 905,553 dogs for a year and identified that 0.20% (1,802 dogs) were affected by this condition.

Certain breeds showed showed significantly high proportions of dogs with cherry eye, including: Neapolitan Mastiffs (4.9%), English Bulldogs (4.8%), Lhasa Apsos (1.6%) and American Cocker Spaniels (1.5%).

Importantly, say the researchers, some popular designer breeds of flat-faced dogs were also hugely affected, such as the Puggle (Pug x Beagle) (2.1%) and Jug (Jack Russell Terrier x Pug) (1.2%), suggesting the recent craze for designer crossbreeds does not eliminate health issues associated with the parental pure breeds.

Overall, brachycephalic breeds had 6.9 times the risk of cherry eye compared with dogs with medium skull length, with the Neapolitan Mastiff at the top of the league table with a risk factor of x34. 

Other findings from the study included:

  • One in every 500 dogs (0.20%) overall in the UK suffer from cherry eye every year
  • The average age at first diagnosis of cherry eye was 0.6 years
  • Seventeen breeds showed increased risk of cherry eye compared with crossbred dogs. The breeds with the highest risk included Neapolitan Mastiff (x 34.3), English Bulldog (x 24.1), Lhasa Apso (x 12.4), American Cocker Spaniel (x 11.6), Puggle (x 9.5), Great Dane (x 6.2), Saint Bernard (x 5.3) and Jug (x 5.2)
  • Sixteen breeds showed reduced risk of cherry eye compared with crossbred dogs. The breeds with the lowest risk included German Shepherd Dog (x 0.03), West Highland White Terrier (x 0.06), English Springer Spaniel (x 0.07), Labrador Retriever (x 0.12) and Lurcher (x 0.12)
  • Purebred dogs had 1.4 times the risk of developing cherry eye compared with crossbred dogs
  • Dogs aged under 1 year were at greatest risk of cherry eye (x 10.8) compared with dogs aged from 2 to under 4 years.

Dr Dan O’Neill, Associate Professor in Companion Animal Epidemiology at the RVC and lead author of the paper, said: “Given that humans designed dog breeds in the first place, we all carry a heavy responsibility to constantly improve our designs to breed away from poor health for these dogs.

"The hugely increased risks of cherry eye in popular flat-faced breeds such as English Bulldogs suggests that we have some way to go before we can consider many flat-faced breeds as designed for optimal health.

"The findings from this study will hopefully help prospective owners make better informed choices when purchasing a dog. We urge all would-be dog owners to follow advice from the UK Brachycephalic Working Group to ‘stop and think before buying a flat-faced dog’.”


  1. O’Neill et al. (2021) “Breed and conformational predispositions for prolapsed nictitating membrane gland (PNMG) in dogs in the UK: A VetCompass study”, PLOS ONE.

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