by Noelle La Croix, DVM, Dip. ACVO
Uveal Cysts – When to Worry
The formation of a uveal, or iris, cyst is a common occurrence in dogs. Canine uveal cysts are usually benign, but they can also be an initial sign of a progressive blinding disease know as pigmentary uveitis. In contrast, feline uveal cysts have been documented solely as benign with a breed predispostion for older Burmese cats. This article will describe the typical characteristics of uveal cysts, uveal melanoma (an ocular and sometimes life-threatening cancer), and iris atrophy (a benign age- and breed-related condition). Potential secondary complications (e.g. uveitis, glaucoma, and cataracts) will also be discussed.
Masses of the iris are classified as either cystic or solid lesions. Cystic iris lesions are believed to arise from the caudal pigmentary epithelia of the iris, or from the epithelia of the ciliary body which produces aqueous humor. Uveal cysts are composed of a single layer of epithelium that is inundated with aqueous fluid. Uveal cysts are described as ‘free floating’ if their location within an anterior chamber changes with head positioning. Uveal cysts are clear or darkly pigmented with uniformly smooth round (or oval) shapes. By contrast, uveal melanomas are solid masses with typically mottled surfaces and irregular shapes. Cysts can also be transilluminated whereas masses cannot. Note that areas of iris atrophy can also be transilluminated, but these areas will change shape during dilation and constriction of the iris. Pigmented uveal epithelia may also be appreciated due the stromal damage of iris atrophy. However, these uniformly flat and darkly pigmented areas should partially transilluminate differentiating them from uveal melanoma. When necessary, ultrasound biomicroscopy performed by a veterinary ophthalmologist can ultimately differentiate between uveal cysts, uveal melanoma, and iris atrophy.
An identified canine uveal cyst may be simply benign or may indicate a more serious disorder. Uveal cysts in Golden retrievers can be a sign of impending blinding pigmentary uveitis. About 50% of Golden retrievers greater than 4 years of age will develop blinding glaucoma within a year of their initial presentation of pigmentary uveitis. There are some characteristics of uveal cysts in the Golden retriever that indicate that they are not benign. Cysts that are a precursor to, or co-presenting sign of, pigmentary uveitis are iridociliary cysts (attached to the ciliary body or the pigmented epithelium of the iris). Iridociliary cysts are best appreciated at the pupillary margin of a dilated pupil (Figure 1). Iridociliary cysts associated with pigmentary uveitis are usually clear-walled and multiple. Other characteristics associated with these cysts include radial pigment deposition on the anterior lens capsule, posterior synechiae, hyperpigmentation of the iris, presentation at the iridocorneal angle, an accumulation of fibrinous material in the anterior chamber, elevated intraocular pressures, and anterior capsular/cortical cataracts (Figure 2). These signs in any breed of dog necessitate treatment for uveitis to prevent a loss of vision. Note that in Golden retrievers, and other breeds, singular thick-wall anterior chamber cysts are not typically associated with the development of pigmentary uveitis. The uveal cysts of Great Danes and English bulldogs have also been associated with the development of glaucoma.
To preserve vision, early referral to a veterinary ophthalmologist to monitor and treat pigmentary uveitis is often vital. Some patients with pigmentary uveitis will develop blinding glaucoma and/or cataracts. These cataracts are not typically excised as postoperative inflammation is assocated with blindness. However, many dogs with pigmentary uveitis will continue to have functional vision throughout their lives if subjected to early treatment.
If you have any further questions or concerns about uveal cysts, or pigmentary uveitis, please feel free to consult with a veterinary ophthalmologist.
Noelle La Croix, DVM, Dip. ACVO
Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800; fax (631) 587-2006