Felis ISSN 2398-2950

Haw's syndrome

Contributor(s): Dennis E Brooks, David Godfrey, Natasha Mitchell


  • Cause: idiopathic but speculatively it may be associated with tapeworm infestation or virus infection.
  • Signs: a syndrome of prolapse of the third eyelids (nictitating membranes) often with diarrhea as well.
  • Occasionally cats can be ill but they will recover with supportive care.
  • Diagnosis: usually just on signs.
  • Treatment: none.
  • Prognosis: good, generally completely benign and self-limiting.
Print off the Owner factsheet Haw's syndrome to give to your client.



  • Idiopathic.
  • Some clinicians think that there is a connection with tapeworm infestations.
  • There is some evidence that the cause is an enteric virus infection. A torovirus-like agent was implicated in one study but this was not supported in a second paper.

Predisposing factors


  • Age (<2 years old).
  • Multiple cat household.
  • Contact with cats which go outside.


  • The condition is idiopathic and very little research has been performed.
  • It is unknown whether there is a single condition or multiple causes with different pathological processes
  • It is likely that there is disease affecting the autonomic nervous system.
  • The main theory for this condition is that an enteric viral infection is the cause.
  • How the virus causes diarrhea or third eyelid protrusion is unknown.
  • It has been assumed that the third eyelid protrusion is caused by a dysfunction of the sympathetic innervation to the third eyelid which when functioning causes the third eyelid to be in the normal retracted position.


  • Weeks to months.
  • May be recurrent.
  • When multiple, cats in a household are affected there is often a couple of weeks between the onset in different individuals.


  • The evidence that this is caused by an infection is that there are (largely anecdotal) reports that the syndrome often affects several cats in a multiple cat household.
  • Some breeding colonies see successive litters of kittens affected.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Smith C H, Meers J, Wilks C R et al (1997) A survey for torovirus in New Zealand cats with protruding nictatating membranes. N Z Vet J 45 (2), 41-43 PubMed.
  • Papasouliotis K & Gruffydd-Jones T (1996) Chronic diarrhea/protrusion of the nictitating membrane in cats and torovirus. Brits VMA in Pract 18, 5.
  • Muir P, Harbour D A, Gruffydd-Jones T J et al (1990) A clinical and microbiological study of cats with protruding nictitating membrane and diarrhea - isolation of a novel virus. Vet Rec 127 (13), 324-330 PubMed.

Other sources of information

  • Mitchell N & James Oliver J (2015) Feline Ophthalmology – The Manual. Natasha Mitchell and James Oliver. Grupo Asis. ISBN 978-84-16315-11-6.
  • BSAVA Manual of Canine and Feline Ophthalmology (2014) 3rd edn. Edited by David Gould and Gillian McLellan. ISBN 978-1-905319-42-8.
  • BSAVA Manual of Feline Practice (2013) Edited by Harvey and Tasker. ISBN 978190531939-8.