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Uveal cyst

• Other names: Iris cyst, iridic cyst, epithelial iris cyst

• Brief description:

Uveal cysts are smooth, round, fluid-filled cysts arising from the iris of the eye. Their color varies from black to clear.

• Cause:

- The cause of uveal cysts is not known, but genetics probably plays a factor.

- Uveal cysts are thought to form from the caudal pigmentary epithelia of the iris, or from the epithelia of the ciliary body which produces aqueous humor, and they are comprised of a single layer of epithelium filled with aqueous fluid.

• Species:

- dogs: most common in hounds, golden retrievers, Labrador retrievers, rottweilers, German shepherds, boxers, Boston terriers, great Danes, and English bulldogs

- cats: rare; most common in Burmese cats or after trauma

- horses: more common in horses with blue eyes

• Signs:

- Black to clear (but usually pigmented) mass in the anterior chamber of the eye (in horses, mass is present in the stroma of the iris)

- Affected dogs and cats usually show no sign of discomfort, unless the cysts are caused by an underlying disorder or trauma

- Horses may show head-shaking or spooking if approached or asked to move toward the affected side if the cyst interferes with their vision, especially if the cysts are mobile.

• Diagnosis:

- Uveal cysts are grossly visible on physical exam, but can be difficult to differentiate from neoplasia.

- The most common way to distinguish between a uveal cyst and melanoma is transillumination; a uveal cyst will become transilluminated, but a melanoma will not. This is done by illuminating the structures with a strong light source placed at an oblique angle to the eye.

- If the masses are free-floating or move when the head or eye moves, it is more likely to be a uveal cyst than neoplasia.

- If the masses are transparent, it is more likely to be a uveal cyst than neoplasia.

- If the masses are smooth and round or oval, it is more likely to be a uveal cyst; uveal melanomas typically have mottled surfaces and irregular shapes.

- In some cases, such as when cysts are very heavily pigmented, ultrasound biomicroscopy may be needed to ultimately differentiate between uveal cysts, uveal melanoma, and iris atrophy.

• Treatment:

- Typically, no treatment is necessary unless the pupil is obstructed and vision is impaired.

- Cysts can be aspirated under anesthesia with a fine needle or deflated with a diode laser. While it's more invasive, the former technique may be preferable in dogs and cats as the deflated cysts are removed from the eye, preventing complications caused by the remnants adhering to other structures. However, in horses, the laser technique is preferable because FNA has higher rates of complications, including uveitis, hyphema, cataract formation, and retinal damage

- Afterwards, patients are treated with topical eye drops +/- oral anti-inflammatories because cyst deflation can generate low-grade inflammation in the eye.

- Most of the time uveal cysts are benign, but may be signs of underlying disease needing further treatment.

- In golden retrievers, uveal cysts are often an early sign of pigmentary uveitis, which is a progressive disease that eventually causes blindness. These cysts are usually transparent and numerous, and may be associated with other signs such as anterior uveitis, glaucoma, corneal edema, corneal ulceration, 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, and anterior capsular/cortical cataracts.

- In Great Danes and English bulldogs, uveal cysts have been associated with the development of glaucoma.

- Uveal cysts in golden retrievers, Great Danes, and bulldogs should be referred to an ophthalmologist for further work-up.

• Prevention: none

• Sources:

- Michael J. Blair, DVM, MS, RPh, Diplomate, American College of Veterinary Ophthalmologists, at Animal Eye Care of Richmond. Conversation and patient discharge sheets. 8/18/20 and 9/22/20.

- Uveal cysts

https://animaleyecare.com/common-eye-diseases/uveal-cysts

- Uveal cyst -- dog

http://www.fmv.ulisboa.pt/atlas/olho/pages_us/olho002_ing.htm

[Image source]

- Uveal Cysts -- When to Worry

https://vmcli.com/uveal-cysts-when-to-worry/

- Dark Mass Inside the Left Eye

https://news.vet.tufts.edu/2019/02/dark-mass-inside-the-left-eye/

[Image source]

- Intraocular Tumors in Small Animal Patients

https://vetmed.illinois.edu/intraocular-tumors-small-animal/

- Anterior Uvea -- Eye Diseases and Disorders

https://www.merckvetmanual.com/eye-diseases-and-disorders/ophthalmology/anterior-uvea

- Equine Clinical Case Challenge – Compulsive Head-Shaking

https://news.vet.tufts.edu/2017/10/equine-clinical-case-challenge-compulsive-head-shaking/

[Image source]

- Equine Case Study: Epithelial Iris Cyst

https://www.severnedgevets.co.uk/blog/equine-case-study-epithelial-iris-cyst