Haw’s syndrome is a relatively common problem in cats. It is a condition where both third eyelids protrude (or prolapse). Protrusion of the third eyelids can occur for many reasons in cats. When it has a sudden onset, and is associated with diarrhea or other gut conditions, it is called Haw’s syndrome.
What is the third eyelid?
The third eyelid, also known as the nictitating membrane or nictitans, is a structure that sweeps over the surface of the eye in order to spread tears across the cornea and protect the eye. It is usually only possible to see the edge of the third eyelid which is located in the lower corner of the eye near the nose. It is often pale pink in colour but can have dark pigment on the surface.
Other names for Haw’s syndrome are:
- Bilateral nictitans protrusion
- Bilateral third eyelid protrusion.
What causes Haw’s syndrome?
Protrusion of the third eyelids occurs for many reasons in cats. It can occur suddenly, and if associated with diarrhoea or other gut conditions, it is known as Haw’s syndrome.
The cause is unknown (therefore it is called an idiopathic condition). There is thought to be an association with diarrhoea caused by a variety of conditions, including tapeworm infestation or virus infection (a toro-like virus has been found in the past, but is not present in every case). Occasionally, other cats in the household will become affected.
Sometimes an affected cat will appear dull or depressed and have no appetite, in which case your vet may undertake a more thorough examination. There are other causes of third eyelid protrusion and of diarrhoea, so these will be considered by your vet.
Haws syndrome can arise at any age but is much more common in young adult cats.
Is there any treatment for Haw's syndrome?
The signs may persist for 4 to 6 weeks, but usually the condition is self-limiting, meaning that it resolves without any specific treatment. All cats recover from the condition, so if protrusion of the third eyelids persist for more than four months, the diagnosis will be reconsidered.
If a cause can be found for diarrhoea, if present, it will be treated specifically. Otherwise, sometimes symptomatic treatment is given for diarrhoea, for example, dietary modification or a worming dose.
Treatment of the eyes is not usually necessary. In extreme cases where vision is being obscured by the third eyelids covering much of the eye, 2.5% phenylephrine eye drops can be used to temporarily reverse the third eyelid protrusion. However, this treatment will not shorten the time course of the syndrome.