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Moon blindness
(Equine recurrent uveitis
ERU)You can find more about horses here
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.
