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Persistent pupillary membranes are remnants of the normal prenatal vascular network that fills the pupillary region. Persistence of pigmented strands across the pupil from one area of the iris to another, or to the lens or cornea, is not uncommon in dogs and occurs occasionally in other species. In Basenjis, the condition is inherited.
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Atrophy of the iris is common in older dogs and may involve the pupillary margin or the stroma. Atrophy of the pupillary margin creates a scalloped border and a weakening of the sphincter muscle, which is manifest as a dilated pupil(s) or by sluggish pupillary light reflexes. Stromal atrophy results in dramatic holes in the iris, and often, displacement of the pupil. Neither form of atrophy appears to affect vision. Animals lacking a functional iridal sphincter may show
increased sensitivity to bright light. |
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Iridic cysts are seen in dogs, cats, and horses. In dogs, they usually are free-floating, pigmented spheres in the aqueous humor within the pupil and anterior and posterior chambers. Although innocuous in most breeds of dogs, anterior uveal cysts (iris and ciliary body) in Golden Retrievers are associated with chronic uveitis, glaucoma, and cataract formation. In cats, the cysts frequently are attached at the pupillary margin. In horses, they are present in the stroma of
the iris and more frequently involve blue irides. Therapy is rarely necessary, but aspiration or laser-induced deflation can be performed. Transillumination will usually demonstrate their cystic nature and differentiate them from neoplasms. Enlarged and cystic dorsal corpora nigra may impair vision and mimic iridic melanomas in horses. Surgical excision or aspiration may be indicated. |
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Anterior uveitis or
iridocyclitis, when acute, is manifest by miosis, increased protein and cells in the anterior chamber, low intraocular pressure, bulbar conjunctival hyperemia, iridal swelling, photophobia, and blepharospasm. Secondary glaucoma, cataract, and corneal opacification may be complications. Concurrent posterior uveitis or choroiditis is frequent. Causes of anterior uveitis can be separated into exogenous and endogenous. Penetrating and nonpenetrating trauma and, rarely,
intraocular neoplasms or intraocular helminths are causes of unilateral uveitis. Common causes of bilateral uveitis include immune-mediated diseases and infectious diseases such as infectious canine hepatitis, feline infectious peritonitis, feline leukemia, feline immunodeficiency, toxoplasmosis, systemic mycoses, canine brucellosis, leptospirosis, malignant catarrhal fever, infectious bovine rhinotracheitis, equine viral arteritis, classical swine fever, canine ehrlichiosis, and
neonatal bacterial infections (joint, navel, and gut) of calves and foals. Recurrent uveitis that is at least in part immune-mediated affects horses (periodic ophthalmia or moon blindness) and dogs (panuveitis with dermal depigmentation or uveodermal syndrome). A thorough history, examination of the cornea for injuries, physical examination, serum serology, and centesis of the aqueous for culture, serology, and cytology aid in diagnosis. |
| Nonspecific therapy consists of topical mydriatics to maintain pupillary dilation and movement, topical corticosteroids (if nonbacterial), a darkened environment, and prostaglandin inhibitors (such as aspirin, flunixin meglumine, or phenylbutazone). If bacterial in origin, topical, systemic, and perhaps intraocular antibiotics are indicated. Treatment of immune-mediated processes may require systemic or subconjunctival as well as topical corticosteroids and oral azathioprine. |
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