Moon Blindness

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Moon blindness
(Equine recurrent uveitis
ERU)

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Introduction

Equine recurrent uveits (or Moon blindness, Recurrent
iridocyclitis) is an inflammatory disease of the eyes of
horses and mules, characterized by sudden onset of clinical
signs which subside, but recur following quiescent periods
of varying length. The iris and ciliary body are primarily
affected, but after repeated occurences, the lens, retina
and vitreous body are involved and vision is impaired.



Moon
blindness

Causes

The cause of periodic ophtalmia has not been clearly
defined. A variety of agents can be responsible for ERU
(virusses, bacteria, parasites, trauma), but also trauma.
The disease is neither heritable nor congenital. Nutrition
studies indicate that there is an inverse relationship
between incidence and the level of riboflavin in the diet.
There is evidence that the disease is more frequent where
the standard of management is poor.

Positive titers for Leptospira bacteria have ben associated
with periodic ophtalmia. Infection by Onchocerca
microfilariae which die in the eye also produces ocular
disease indistinguishable from periodic ophtalmia. There is
evidence that the ocular inflammation may be a localized
hypersensitivity or allergic reaction following secondary
infection or toxinaemia.

Incidence

ERU probably occurs throughout the world. In the USA, the
disease is more frequent on the eastern seaboard and, to a
lesser extent, in the Missisippi and Ohio River Valleys. It
is rare in the Rocky Mountains, west coast and southwest
regions. Ordinarily, the incidence is low. Occasionally,
outbreaks involve a rather high percentage of a group. The
disease is recognized more frequently in mature horses and
mules, probably because the lesions are more pronounced and
diagnosis is less difficult.

However, the disease has been observed in animals as young
as 3,5 months of age.

Clinical
Findings and Diagnosis

The
acute signs appear suddenly, then gradually abate in a few
days to a week or more to be followed by a quiescent period
which may last for only a few days or, in extreme cases,
for several years. Repeated acute exacerbations often
occur.

In the acute stage, there is sudden onset of photophobia
and lacrimation involving one or both eyes. This may be
associated with slight depression and a moderate elevation
of the body temperature. Attention is drawn to the affected
eye by its extreme sensitivity to light, the closed eyelid
and the excessive lacrimation. Careful examination reveals
a severe conjunctivitis, with or without some opacity of
the cornea. A cellular exudate which may produce a simple
diffuse cloudiness of the aqueous humor or a yellowish,
flocculent exudate which settles to the lower half of the
anterior chamber is present.



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