◊ 9-Anterior Uvea ◊
ANTERIOR UVEAL (IRIS and CILIARY BODY) AFFECTIONS
I-CONGENITAL ABNORMALITIES OF ANTERIOR UVEA: -
1-Persistent pupillary membranes: -
It is a remnant of the pupillary membrane, which closes the pupil during fetal life, in a form of pigmented or non-pigmented strands. In the fetus, the pupil is closed with a thin pupillary membrane that starts to be absorbed directly before birth. When absorption is not complete a strands are formed, these strands may dissappear 4-5 weeks after birth.
1-These strands may extend from one part of the iris to another, from the iris to the lens or to the cornea, or it has free end.
2-Strands from iris to cornea may cause corneal opacity and strands from iris to lens may produce cataract but those from iris to iris have no clinical signs.
This condition does not reduce functional vision significantly and thus does not require surgical intervention.
2-Iris coloboma, Iris hypoplasia, or Iris atrophy: -
Iris coloboma is a full thickness defect of the iris.
1-The defect may be confined to the base of the iris (iridodiastasis) or may involve a portion of the pupillary margin and form a notch giving the pupil a "dumbbell" shape. The number of defects varies and in some cases the colobomata are so numerous that the iris has the appearance of spider web.
2-The colobomata changes in shape as the pupil is constricted or dilated.
Functional vision of the animal is not significantly involved therefore treatment is not indicated
3-Iris cyst: -
Cysts of the iris arise from the pigmented epithelial layer of the iris and ciliary body. Most of them are congenital and some are acquired due to iris irritation and degeneration.
A-Pupillary cyst: -
It is originating from the pupillary margin of the pupil. This type is common in dogs. Large ones may anchor to the corneal endothelium and produce local corneal edema. Surgical removal is not recommended unless causing corneal irritation.
B-Posterior chamber cyst: -
Originates from the posterior surface of the iris and is not seen until the pupil is dilated. Treatment is not recommended.
C-Stromal iris cyst: -
Present in the iris stroma it self. It is common in equine. It may be single or multiple and located near the base of iris. Trans-illumination clarifies its hollow appearance. Treatment is not recommended.
D-Vitreous cyst: -
Originate from the ciliary body and usually develop between the lens and vitreous humour. No treatment is recommended.
E-Free cyst: -
It is detached from the iris and float freely in the anterior or posterior chamber. It can affect the aqueous flow and its removal in such case is recommended. Also the cyst can be aspirated through a limbal paracentesis using a fine needle.
It is the presence of a difference in the color of the iris in both eyes or part of one iris has a different color. The difference in color may be hypopigmentation or hyperpigmentation. It is a common affection in buffaloes and need no treatment.
Total absence of iris
Presence of more than one pupil
7- Ancoria: -
Absence of pupil
Abnormal shape of the pupil.
II-ACQUIRED DISEASES: -
1-Anterior uveitis: -Definition:
It means inflammation of the iris and ciliary body (anterior uvea)
The determination of the exact cause of anterior uveitis is considered to be one of the most difficult problems in ophthalmology
A-Exogenous causes: -
Direct trauma to the eye or the introduction of infection by perforating wounds. Intraocular surgery may produce some degree of anterior uveitis.
B-Spreading of inflammation from other parts of the eye: -
Deep and ulcerative keratitis has concurrent anterior uveitis.
C- Specific disease: -
Dogs (Infectious hepatitis, leukemia and heartworms)
Cats (Infectious feline peritonitis, feline leukemia and toxoplasmosis)
Equine (Leptospirosis, brucellosis and Onchocerca cervicalis)
Bovine (Malignent catarrhal fever, and Pink eye)
Sheep and goat (Mycoplasma)
D-Hypersensitivity: -E-Presence of a primary focus of infection in the animal body: -
Infection goes through the blood stream sensitizing the anterior uvea (tonsils,teeth, anal sacs and prostate).
In many cases the cause cannot be determined.
Anterior uveitis may be acute or chronic, unilateral or bilateral. If the cause is a systemic disease it is usually bilateral and if the cause is hypersensitivity it is usually unilateral
1-Blepharospasm, excessive tearing, eye rubbing and conjunctivitis.
2-Circum-corneal injection of the conjunctival and ciliary blood vessels
4-Abnormal contents of the anterior chamber. It starts out as increased aqueous flare then hyphaema, fibrin clots and hypopyon may be observed.
5-Iris changes, as the iris becomes rough, dull in color and swollen in appearance. The pupil is constricted due to exhaustion of the dilator muscles. The more acute the lesion, the more severe the miosis. The superficial blood vessels of the iris become congested and may give a red appearance to the iris.
6-Posterior synechiae may develop due to adhesion of the iris to other structures mainly to the lens. Focal adhesion will result in an irregularly shaped pupil and opacity of the lens capsule. Adhesions may prevent aqueous flow into the anterior chamber and the iris bulges (iris bombe), the filtration angle is obliterated and secondary glaucoma develops.
7-Intraocular pressure is hypotonic in early cases then hypertonic in later stages due to obstruction of the filtration angle by fibrin clot or hypopyon.
1% atropine solution is the drug of choice. It is beneficial in that it is mydriatic, cycloplegic and decongests the iris
Cause inhibition of the immune medicated uveal response and reduce uveal congestion. Corticosteroids are given systematically, topically and subconjunctivally.
Less important than atropine and corticosteroid therapy
4-Supportive treatment by keeping the animal in dark room and application of worm compresses
1-Peripheral anterior synechiae 2-Posterior synechia
2-Equine periodic ophthalmia, Equine recurrent ophthalmia, or Moon blindness: -
Moon blindness has been recorded as early as the fourth century AD. The recurrent nature of the disease has long been recognized and associated with changes in the lunar rotation. The disease is common and an incidence up to 12% has been recorded in eastern areas of the United States. There is no age, sex or breed predilection.
The condition is probably hypersensitivity. Any disease capable of producing chronic or recurrent sensitization of the vascular tunic of the eye must be considered.
1-Deficiency of vitamins A, B, and C 2-Leptospirosis 3-Brucellosis
4-Streptococcal hypersensitivity 5-Onchocerca cervicalis
Moon blindness is the most common cause of blindness in horses and mules.
1-Blepharospasm and photophobia 2-Catarrhal conjunctivitis
3-Circum-corneal ciliary injection 4-Cloudiness of the cornea
5-Aqueous flare, hyphaema, and hypopyon 6-Miosis
7-Anterior and posterior synechiae 8-Complicated cataract
9-Retinal edema or detachment
1-Mydriatics, topical atropine to relieve the ciliary spasm and dilate pupil
2-Antibiotics, antihistamines and vitamins have little effect on the course of the condition.
3-Anti-inflammatory agents are administered parenterally, topically and subconjunctivally.
4-Additional therapy can be used according to the cause.
The database that may be informative for differentiating known uveitis etiologies includes: CBC, BUN, enzymes, total protein, electrophoresis, toxoplasmosis titer, leptospirosis liter, viral antibody titers, conjunctival biopsy, anterior chamber paracentesis and a stool sample for parasites.
3-Anterior uveal tumors: -
Iris tumors can be detected easily before they become extensive, but ciliary body tumours are seldom diagnosed until they cause serious damage to the eye. Small iris tumors can be surgically removed. Massive tumors of the iris and ciliary body should be treated only by removing the eye.