Introduction:

Head shaking in the horse is a well recognized, common problem
with no preference for age, gender or breed. Usually the problem
worsens while exercising but can be seen at anytime. Diagnosis is
difficult and treatment frequently unrewarding. Recently sunlight
was implicated as one of the causes, resembling photic sneezing
in humans. This has provided a successful way to treat some of
theses horses. Causes implicated in head shaking have been:

Light
Middle Ear Diseases
Ear Mites
Cranial Nerve Diseases
Eye Diseases
Guttaral Pouch Infection
Teeth Problems
Allergic Rhinitis
This article deals with the diagnosis and treatment of this
frustrating problem.


Diagnosis:

Certainly the first thing to try is to see if working out of the
sunlight helps. If not attempt blindfolding to determine if the
problem has some relationship with the brightness of light. It
is imperative to exhaust this avenue. Photic head shaking is
poorly understood. Treatment with cyproheptidine probbly should
be attempted, even if the problem does not seem light
responsive.

And exhaustive exam would include:

Physical exam
Opthalmic exam
Otoscopic exam
Endoscopic exam of the upper respiratory tract and guttaral
pouches
Radiography of the skull
Complete blood count and chemistries
Occasional y one of theses exams will turn up a significant
finding but usually the problem continues undiagnosed.


Treatment:

A course of cyproheptidine at 0.3 mg/kg of body weight twice
daily should be attempted. If the horse was found to worsen with
increasing light levels the chance of success is greatly increase.
Improvement occurs within 24 hours of starting treatment. Fly
masks with the eye area covered in shading material has been
effective for these horses.

Other treatment would be to address the specific problems
identified on the diagnostic work up. Other non specific
treatment that has occasionally been helpful is corticosteroids.
This is most effective for allergic rhinitis. Fly masks that
cover the ears may help is some cases. Unfortunately treatment is
frequently unrewarding.