Equine Recurrent Uveitis
Encyclopedia
Equine Recurrent Uveitis, ("Moon Blindness", Recurrent Iridocyclitis) is an acute, non-granulomatous inflammation
of the uveal tract
of the eye
, occurring commonly in horse
s of all breeds, worldwide. The causative factor is not known, but several pathogeneses have been suggested. It is the most common cause of blindness in horses. In some breeds, a genetic factor may be involved.
It has been suggested that the disease is primarily auto-immune in nature, being a delayed hypersensitivity
reaction to any of the above agents.
is present, with signs of ocular pain, usually blepharospasm
, increased lacrimation and photophobia
. Miosis
is also usually present. After a few days, this will progress to a keratitis
and iridocyclitis
. Other ocular problems may also occur, including conjunctival and cornea
l oedema, and aqueous flare.
After an acute flare-up, there may be no clinical signs of disease for a prolonged period, which can vary from a few hours to a few years. When there are frequent acute incidents, additional clinical signs may be seen, including anterior and posterior synechiae, poor pupil
lary responses, cataracts, and a cloudy appearance to the vitreous humour
.
, but only in the hands of an expert.
is important, as pupillary constriction is the primary reason for pain. Anti-inflammatory therapy is usually given both systemically, often in the form of Flunixin Meglumine, and topically, as prednisolone acetate. The mydriatic of choice is atropine
. In the periods between acute attacks, no therapy has been shown to be beneficial.
.
, which has a higher than usual incidence of blindness.
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
of the uveal tract
Uvea
The uvea , also called the uveal layer, uveal coat, uveal tract, or vascular tunic, is the pigmented middle of the three concentric layers that make up an eye. The name is possibly a reference to its reddish-blue or almost black colour, wrinkled appearance and grape-like size and shape when...
of the eye
Equine vision
The equine eye is the largest of any land mammal. Its visual abilities are directly related to the animal's behavior and the fact that the horse is a flight animal...
, occurring commonly in horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s of all breeds, worldwide. The causative factor is not known, but several pathogeneses have been suggested. It is the most common cause of blindness in horses. In some breeds, a genetic factor may be involved.
Aetiology
There are several suggested aetiologies, and any combination of these may be present in any given case.- Vitamin deficiency (AVitamin AVitamin A is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is necessary for both low-light and color vision...
, B or CVitamin CVitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient for humans and certain other animal species. In living organisms ascorbate acts as an antioxidant by protecting the body against oxidative stress...
) - Viral infection
- Bacterial infection
- LeptospiraLeptospiraLeptospira is a genus of spirochaete bacteria, including a small number of pathogenic and saprophytic species...
- StreptococcusStreptococcusStreptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...
- BrucellaBrucellaBrucella is a genus of Gram-negative bacteria. They are small , non-motile, non-encapsulated coccobacilli, which function as facultative intracellular parasites....
- Leptospira
- Parasitic infection
- Strongyle
- Onchocerca cervicalisOnchocercaOnchocerca is a genus of roundworm. It contains one human parasite - Onchocerca volvulus - which is responsible for the neglected disease Onchocerciasis, also known as "River Blindness" because the infected humans tend to live near rivers where host black flies live...
- Auto-immune
It has been suggested that the disease is primarily auto-immune in nature, being a delayed hypersensitivity
Hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...
reaction to any of the above agents.
Clinical Signs
In the acute stage of the disease, a catarrhal conjunctivitisConjunctivitis
Conjunctivitis refers to inflammation of the conjunctiva...
is present, with signs of ocular pain, usually blepharospasm
Blepharospasm
A blepharospasm , is any abnormal contraction or twitch of the eyelid....
, increased lacrimation and photophobia
Photophobia
Photophobia is a symptom of abnormal intolerance to visual perception of light. As a medical symptom photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical photosensitivity of the eyes, though the term...
. Miosis
Miosis
Miosis is the constriction of the pupil of the eye to two millimeters or less...
is also usually present. After a few days, this will progress to a keratitis
Keratitis
Keratitis is a condition in which the eye's cornea, the front part of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves impaired eyesight.-Types:...
and iridocyclitis
Iridocyclitis
Iridocyclitis, a type of anterior uveitis, is a condition in which the uvea of the eye is inflamed.Iridocyclitis isInflammation of the iris and the ciliary body.- Symptoms :Symptoms include:* Photophobia* Redness* Watering of the eyes* Lacrimation...
. Other ocular problems may also occur, including conjunctival and cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
l oedema, and aqueous flare.
After an acute flare-up, there may be no clinical signs of disease for a prolonged period, which can vary from a few hours to a few years. When there are frequent acute incidents, additional clinical signs may be seen, including anterior and posterior synechiae, poor pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
lary responses, cataracts, and a cloudy appearance to the vitreous humour
Vitreous humour
The vitreous humour or vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates...
.
Diagnosis
The cornerstone of diagnosis is an accurate history, and a good clinical examination of the eye, in order to eliminate traumatic uveitis. Ultrasonography is a useful tool, as it can detect a thickened irisIris (anatomy)
The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
, but only in the hands of an expert.
Treatment
During an acute flare-up, therapy is targeted at reducing the inflammation present, and dilating the pupil. MydriasisMydriasis
Mydriasis is a dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day...
is important, as pupillary constriction is the primary reason for pain. Anti-inflammatory therapy is usually given both systemically, often in the form of Flunixin Meglumine, and topically, as prednisolone acetate. The mydriatic of choice is atropine
Atropine
Atropine is a naturally occurring tropane alkaloid extracted from deadly nightshade , Jimson weed , mandrake and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a drug with a wide variety of effects...
. In the periods between acute attacks, no therapy has been shown to be beneficial.
Prognosis
Horses that suffer from this disease can never be considered cured, although they can be managed by careful use of the therapy described above, and fast detection of new flare-ups. If the disease is not properly treated, it will eventually lead to blindnessBlindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
.
Genetics
There is a genetic component to ERU in some breeds of horse, notably the AppaloosaAppaloosa
The Appaloosa is a horse breed best known for its colorful leopard-spotted coat pattern. There is a wide range of body types within the breed, stemming from the influence of multiple breeds of horses throughout its history. Each horse's color pattern is genetically the result of various spotting...
, which has a higher than usual incidence of blindness.