Basic HTML Version
MOON B L I NDN E S S
Equine recurrent
uveitis
(ERU)
Veterinary Surgeon
Chris Dixon
XLVets Practice
Paragon Veterinary
Group, Carlisle
Chris Dixon BVSc MRCVS,
Paragon Veterinary Group
9
EQUINE MATTERS
E
quine recurrent uveitis (ERU) also known as moon blindness and periodic
ophthalmia can be a serious and debilitating disease. ERU is the most
common cause of blindness in the horse, has been reported since the 4th
century AD and continues to be a problem in many breeds and crosses
around the world today.
What is uveitis?
The term relates to inflammation inside the
eye and in the syndrome ERU it will
characteristically come back time and time
again. Historically the disease was thought
to be caused by the movement of the moon
and hence the term moon-blindness.
Over the years many studies in different
countries have tried to find the cause of ERU
and we now know that the disease is related
to a stimulation of the horse's immune system.
However ERU does not have a single cause
and many factors may contribute to its
inception. Studies have demonstrated links to
genetic makeup, bacterial and viral infection,
trauma and UV light.
The number of affected horses varies around
the world. Thankfully the UK does not appear
to be as severely affected as parts of Europe
and the USA, where it can be seen in as
many as 1 in 4 horses. However, very few
surveys have been conducted in the UK and
an exact number of cases diagnosed each
year has not been recorded.
ERU is seen more commonly in Appaloosas
and Warmbloods, however it has been seen
affecting most breeds from Falabella ponies
to Clydesdales. It is a debilitating disease
because it causes a painful spasm of the
muscle inside the eye pulling the pupil into
a small slit. The horse's vision is severely
impaired and the surface of the eye (the
cornea) can become cloudy or opaque.
Cataracts may develop and the disease
process can also damage the retina (which
normally translates light into electrical signals
passed on to the brain). A horse may recover
from a single bout of uveitis with minor
inflammatory damage, but the effect is
compounded each time it occurs.
ERU classic presentation. Left eye with cloudy
cornea, small constricted pupil and pus pooling
inside the eye.
ERU chronic presentation. Right eye iris colour
is now dark and bands connect it to the
surface of the lens through the pupil.
'Butterfly' lesions seen at the back of the eye
with ERU.