Chapter 7 Uvea
The internal vascular layers of the eye—the iris and ciliary body in the anterior segment and the choroid of the posterior segment—make up the uvea. These layers are composed of dense networks of blood vessels of various sizes and have varying degrees of pigmentation. Consequently, the pathology that affects these layers reflects their vascular basis—inflammation, hematogenous spread of infectious agents, and neoplasms. The most significant lesions of the uvea are inflammatory. Various congenital uveal abnormalities, often hereditary, such as colobomas and persistent pupillary membranes, pigmentation variations, uveal cysts, and tumors, are also frequently seen in small animal practice.
Figure 7-3 Iris coloboma extending nasally in an Australian shepherd. A coloboma is a congenital defect—in this case, in the nasal iris—that involves the sphincter muscle. Iris colobomas are hereditary in this breed and can be associated with multiple ocular anomalies.
Figure 7-5 Australian shepherd with dyscoria. Dyscoria is abnormally shaped pupil; usually a dyscoric pupil is not round and is eccentric in the iris. The condition is hereditary in Australian shepherds and is associated with multiple ocular anomalies.
Figure 7-8 Iris-to-lens persistent pupillary membrane (PPM). PPMs are remnants of the vasculature that fills the anterior chamber during fetal development of the eye. Iris-to-lens PPMs are usually associated with cataracts where the PPM touches the lens capsule.
Figure 7-14 PPM remnants on the lens capsule. Linear opacity is a hair on the cornea. These small pigment deposits on the anterior lens capsule are seen in many dogs and rarely cause any vision-related or other problems. The heritability of these types of deposits is unknown.
(Courtesy Dr. Robert Playter.)
Figure 7-34 Free-floating iris cyst in anterior chamber in a dog; note the transillumination of the tapetal reflex through the cyst. These cysts must be distinguished from iris melanomas and rarely need treatment.