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Cataracts are an opacity of the lens or its capsule and should be differentiated from the minor lens imperfections in young dogs and the normal increase in nuclear density (nuclear sclerosis) that occurs in older animals.
Cataracts usually are classified by their age of onset (congenital, juvenile, senile), anatomic location, cause, degree of opacification (incipient, immature, mature, hypermature), and shape. Most cataracts can be detected by dilating the pupil and examining the pupillary region against the retroillumination of the tapetal fundus. Slit lamp biomicroscopy permits optimal direct examination of the lens. Cataracts (often inherited) are more common
in dogs than in other species (see
Table:
Inherited Cataracts in Domestic Animals ). Other etiologies include diabetes mellitus, malnutrition, radiation, inflammation, and trauma. In cats and horses, most cataracts are secondary to anterior uveal inflammation. Sight may be regained in young dogs, cats, and horses when cataracts undergo sufficient spontaneous resorption; congenital nuclear cataracts in young ani mals may reduce in size with growth of the lens to permit restoration of vision as the animal matures. Animals with
immature and incomplete cataracts may benefit from topical ophthalmic atropine 2-3 times/wk, which allows vision around a central cataract. In general, the only definitive therapy for cataracts is surgical removal of the lens. In dogs, cataract extraction, often by phacoemulsification, yields best results when performed before cataract maturation is complete and lens-induced uveitis, due to leakage of lens material, is established. Lens-induced uveitis is intensified by cataract
surgery and contributes substantially to postoperative complications. In animals in which cataract surgery is not performed, continued clinical monitoring is important. The secondary lens-induced anterior uveitis often requires longterm corticosteroid therapy and occasional mydriasis. Secondary glaucoma and phthisis bulbus formation are possible complications. |
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Lens displacement (subluxation, anterior or posterior luxation) occurs in all species but is common as a primary inherited defect in several terrier breeds. Complete displacement into the anterior chamber produces acute signs and frequently is accompanied by glaucoma and corneal edema. Treatment is surgical removal. Posterior displacement into the vitreous cavity is asymptomatic or associated with ocular inflammation or glaucoma. Subluxated lenses are recognized by an
aphakic crescent and trembling of the iris (iridodonesis) and lens (phacodonesis). The decision to remove subluxated lenses is based on the severity of ocular disease that can be attributed to the lens displacement. Lens displacements also can be produced by trauma, enlargement of the globe with glaucoma, and degenerative zonular changes with hypermature cataracts. Procedures to remove the lens for lens displacement are associated with higher levels of postoperative complications of
glaucoma and retinal detachment. |
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