Looking at iridociliary cysts

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Iridociliary cysts in dogs and cats occur when part of the epithelium fills with aqueous humor. It may become separated from the iris, which causes a round mass to form and float within the anterior chamber. In an educational session at the Veterinary Meeting & Expo (VMX) hosted by the North American Veterinary Community (NAVC), Kate Myrna, DVM, DACVO, a professor at the University of Georgia in Athens, also explained that iridociliary cysts (also known as iris or uveal cysts) typically originate in the back of the pigmented epithelium of the iris or ciliary body of the iris.¹

“They’re little, fluid-filled sacs. They are usually incidental, but there are a couple of exceptions to this,” Myrna told VMX attendees.

Identifying iridociliary cysts

In some cases, an iridociliary cyst can obstruct a patient’s vision. If needed, these benign cysts can be ruptured with a diode laser.¹

“In dogs, because of gravity, these balls will usually float to the bottom of the anterior chamber, and when you light them from the side, you'll be able to see through them. There can be one, there can be multiple. You can start with one and end up with more later. And sometimes they can sneak back behind the pupil. So you maybe saw [a cyst] one day and the next day you didn’t see one at all. They do float,” Myrna said. “Feline iris cysts more typically extend from the pupillary margin and are much darker.”

Myrna emphasized that smoothness and shape are key to identifying a cyst associated with the iris, and they often transilluminate with a bright light. “They look like an emulated balloon, and tumors just don't grow like that. You can't see the light pass through the tumor,” she said.

During her talk, Myrna verbally walked attendees through a series of close-up images of iridociliary cysts in patients. One image of a canine patient served as an example of a cyst that was almost fully translucent. “This was a gold star day because a student spotted this on their exam, and I about lost it,” Myrna said. “I was so excited, because it is virtually invisible, and that's just because the iris tissue is so light.”

Disease linked to iridociliary cysts

According to Myrna, iridociliary cysts are associated with an inflammatory condition that is sometimes referred to as golden retriever uveitis.¹ The disease occurs exclusively in golden retrievers, golden and labrador retriever cross bred dogs and golden retriever and poodle cross bred dogs.²

“Those cysts stay behind the iris, and they are exfoliating pigment. So, you can imagine, as the pupil constricts, the cysts rub on the lens, and they leave these streaking pigment lines,” Myrna said. “Now we call it uveitis because frequently it has this big, bloody cyst that juices out a bunch of gross fluid.”

Golden retriever uveitis disease is progressive with cysts continuing to grow and darken, and, in more serious cases, secondary glaucoma may develop, which can lead to eye loss. “It does not act like uveitis in that anti-inflammatories don’t seem to change the course of the disease,” Myrna said.

Most dogs diagnosed with golden retriever uveitis are older than 5 years, and the average age at the time of diagnosis is 8-10 years.¹ The disease prevalence in North America is estimated to be between 5% and 10%, according to Myrna.¹ “This is much more common in the northeast and the Midwest,” she added.

Takeaway

Iridociliary cysts can cause vision interference, but are benign in nature. However, Myrna noted that their primary importance in identifying an iridociliary cyst lies in “differential diagnosis” from iris melanoma.

References

1. Myrna K. I’m seeing spots! What to do with brown spots in the eye. Presented at: Veterinary Meeting & Expo; Orlando, FL. January 25-29, 2025.
2. Golden retriever uveitis—what dog owners need to know. Veterinary Vision Center. October 1, 2021. Accessed January 29, 2025. https://veterinaryvisioncenter.com/golden-retriever-uveitis-what-dog-owners-need-to-know/