Headshaking is an extremely frustrating and disabling condition for affected horses and their owners.
It may manifest as just an occasional nod or jerk of the head, or it may develop into violent, exaggerated head movements that prevent any work or training.
It is often seasonal and linked to bright sunlight.
The list of possible causes seems almost endless, from allergies to photophobia, neuralgia to ear mites and toothache to sinusitis.
And treatments are wide-ranging — nose nets, antihistamines, anticonvulsants, surgery on the nerves, dental work, ear plugs — you name it, it has probably been tried.
The fact that no one therapy works for all shows the problem cannot have just one cause: the headshaking is a sign of irritation, stress or distress which may be caused by any number of factors.
Cambridge University vets have recently reported another therapy: sodium cromoglygate eye drops.
In a number of horses, seasonal and light-stimulated head-shaking was either cured or significantly improved by daily usage.
The drug is normally used to control allergic asthma in humans as it prevents the liberation of allergic chemicals by cells of the immune system.
Just how or why it might work in the eyes of head-shaking horses is unclear, but it does, and it gives vets another tool in their growing head-shaking treatment toolbox.
This article was first published in Horse & Hound (27 November, 08)