Dog Eye Melanoma: Types, Symptoms, and Treatment

Dog eye melanomas are darkly pigmented tumors that can occur inside the eye or on the surface of the eye. Thankfully, most are benign, but they can still be worrisome. To help dog parents know what to expect, integrative veterinarian Dr. Julie Buzby discusses the types, symptoms, diagnosis, treatment, and prognosis for dog eye melanoma.

When you hear the word “melanoma” you may think about a dangerous skin cancer in humans. Or maybe you think about a mass in a dog’s mouth or a tumor on a dog’s paw. But what you may not know is that dogs can also develop melanomas inside their eye (uveal melanoma) or on the surface of the eye (limbal melanoma).

Let’s take a closer look at these two types of dog eye melanomas and what they might mean for your canine companion.

What are the types of dog eye melanoma?

As mentioned, dog eye melanomas will originate from one of two locations—the uvea or the limbus.

The first location, the uvea, is actually a collection of three structures within the eye. It includes the iris (i.e. the colored portion of the eye), the ciliary body (which lies just behind the iris), and the choroid (i.e. the middle layer of the back of the eye).

And the other location, the limbus, is the junction between the cornea (the clear front part of the eye) and the sclera (the white, outermost part of the eye).

Uveal melanoma

While relatively uncommon overall, uveal melanomas are the most common primary intraocular tumor in dogs. The majority of uveal melanomas come from the iris or ciliary body, but some can develop from the choroid. Thankfully, over 80% of uveal melanomas are benign.

The remaining 20%, which are malignant, tend to be locally invasive. This means that they can grow into other parts of the eye or, in rare cases, into the brain. However, occasionally, a malignant melanoma can also spread to other parts of the body like the lungs, liver, or regional lymph nodes.

Uveal melanomas are typically round, raised, brown or black pigmented masses. Iris melanomas are usually firmly attached to the iris and can often distort the size and shape of the iris. Alternatively, you might see a mass peeking through the pupil if it originated from the ciliary body. However, since the choroid is in the back of the eye, it wouldn’t be possible to see a choroidal melanoma just by looking at your dog’s eye.

While dogs can develop a uveal melanoma at any age, they are more common in middle-aged to older dogs with an average age of nine years.

Limbal melanoma

Also known as epibulbar melanomas, limbal melanomas originate from the pigmented cells within the limbus. Since the limbus is on the outside of the eye—between the cornea and sclera—limbal melanomas are usually much easier to notice than uveal melanomas.

Most limbal melanomas are rounded, smooth, well-demarcated, and brown or black-colored growths. However, it is possible for a dog to develop an amelanotic melanoma (i.e. one that lacks obvious pigment). Limbal melanomas tend to appear on the side of the eye that is furthest away from the nose.

Melanomas arising from the limbus tend to grow very slowly and are almost always benign tumors. However, if they continue to grow, limbal melanomas can harm the cornea and the sclera. And in extreme cases, these tumors can affect so much of the eye that they lead to vision impairment.

Overall, limbal melanomas are more common in young dogs and senior dogs. However, they can occur at any age.

What causes eye melanomas in dogs?

Like many other types of tumors, the underlying cause of uveal and limbal melanomas in dogs is unknown. But researchers believe genetics may play a role. It is possible that dogs with greater skin pigmentation may have a higher risk of ocular melanomas. The breeds most likely to develop eye melanoma are:

• Labrador Retrievers
• Golden Retrievers
• German Shepherd dogs
• Schnauzers
• Cocker Spaniels

Current research does not support any environmental factors as a cause for ocular melanoma. So, for now, it seems unlikely that UV-ray damage from sunlight is a factor. However, we do know that dogs who spend a lot of time outdoors may be more likely to develop cataracts in dogs. Thus, it may still be a good idea to break out the Doggles (or other dog eye UV protection) when you go hiking or boating with your canine companion.

What are the symptoms of dog eye melanoma?

Based on the fact that limbal and uveal melanoma occur in different locations on the eye, it makes sense that they would have different symptoms.

Uveal melanoma symptoms

Since uveal melanomas grow within the eye, they are harder to notice in the early stages. This is especially the case for ones that arise from the ciliary body or choroid because those structures are hidden behind the iris and in the back of the eye. But even iris melanomas can be easy to miss at first because the iris is already highly pigmented.

In the early stages of uveal melanoma, the dog may be asymptomatic. And you may not know anything is wrong until the tumor is large enough for the vet to visualize it on a physical examination or it starts causing problems.

Eventually, with uveal melanomas that develop in the front of the eye, you may start to see changes in the appearance of the eye. For example, you might notice that the iris has changed shape (i.e. dyscoria). Or you may see blood in the front chamber of the eye (i.e. hyphema).

Additionally, intraocular tumors like uveal melanoma can cause increased pressure within the eye (i.e. secondary glaucoma in dogs). The discomfort associated with glaucoma can cause headshaking, squinting, eye-rubbing, and whining.

Limbal melanoma

Unlike uveal melanomas, limbal melanomas can easily be seen with the naked eye (no pun intended). This makes it easier to detect them in the early stages. Dogs are often asymptomatic at first. However, sometimes limbal melanomas can grow large enough that it becomes difficult for the dog to close the eyelids.

Also, if other surrounding eye structures are involved, limbal melanomas may cause excess tear production and redness or inflammation. And while limbal melanomas don’t usually affect intraocular pressures, they can be painful once they infiltrate the cornea.

Symptoms of both melanoma types

Vision loss is possible with both melanoma types. But because only one eye is affected, dogs may compensate with the opposite eye. Thus, they may not show obvious symptoms of blindness.

Other possible side effects from dog eye melanoma include:

• Uveitis (i.e. uveal inflammation)
• Buphthalmos (i.e. a bulging, enlarged eyeball)
• Lens subluxation (i.e. lens partially moving out of place)
• Retinal detachment

How is ocular melanoma diagnosed?

If you notice a dark spot on your dog’s limbus or iris, or if you see other eye symptoms, schedule a veterinary visit. Your vet can help you figure out what the next steps should be.

It isn’t possible to determine if a melanoma is benign or malignant based on appearance alone. And there are several other conditions (e.g. iridial cysts and iris nevus/freckles) that can look like a melanoma. Therefore, if your vet suspects ocular melanoma or finds any ocular pigmented masses bigger than three millimeters wide, he or she may refer you to a veterinary ophthalmologist for a more in-depth evaluation.

Depending on what the ophthalmologist sees on the ophthalmic exam, he or she may recommend additional testing such as gonioscopy (i.e. looking at the area where the iris and cornea meet), ultrasound, or magnetic resonance imaging (MRI). These tests allow the ophthalmologist to further evaluate the tumor and the eye itself.

Since many uveal melanomas and almost all limbal melanomas are benign, the vet or veterinary ophthalmologist may not recommend diagnostic staging to look for signs of metastatic disease at first. However, staging may be a good idea if the tumor type is unknown or if your dog has any signs of skin or oral cancer. Typically staging involves bloodwork, urinalysis, X-rays or ultrasound, and/or fine needle aspiration of nearby lymph nodes.

Additionally, if the veterinarian or veterinary ophthalmologist removes the mass (or the entire eye) he or she can submit it for biopsy. This is the best way to reach a definitive diagnosis for a tumor of the eye in dogs.

What is the treatment for dog eye melanoma?

After completing the diagnostics, the vet or veterinary ophthalmologist will discuss the treatment options. Dog eye melanoma treatment will vary depending on the type of melanoma and how it is affecting the eye.

Monitoring the tumor

In the early stages of uveal melanoma, or with small, slow-growing limbal melanoma, your veterinarian might choose to monitor the tumor at first. He or she will probably have you check in every one to three months initially. And the vet may take pictures of the eye each time for comparison.

But if the mass is large, painful, or growing rapidly, your vet will probably recommend considering treatment.

Surgical removal or laser therapy

Surgical removal is an option for some tumors involving the limbus or iris. A veterinary ophthalmologist will usually perform this surgery. Alternatively, diode laser treatment for iris melanoma or ciliary body melanoma has a high success rate. In some cases, especially with limbal melanoma, the veterinary ophthalmologist may consider combining debulking of the tumor (i.e. removing as much as possible) and diode laser therapy to decrease the chances of reoccurrence.

Enucleation

If the entire tumor cannot be surgically removed, is growing rapidly, or is causing glaucoma, pain, or other complications, your veterinarian may talk to you about removing the eye entirely (i.e. enucleation). This sounds like a scary option. But keep in mind that many dogs adapt quickly and easily to having one eye.

Enucleation is also the fastest way to alleviate pain and symptoms from invasive ocular melanoma. It does not require long-term use of eye medications or following up with the vet every few months. And submitting the entire eye for analysis is the easiest way to reach a definitive diagnosis. Enucleation is also the most cost-effective treatment option.

Additional options

There are also a few other treatments that may help in some situations.

• Cryotherapy may be an option for limbal melanoma treatment, but it only stops cancer cells from growing. It does not shrink the tumor.
• The melanoma vaccine for dogs (usually available through veterinary oncologists) might not help with treating eye melanomas. But there is some data to suggest that it can help with the metastatic disease caused by uveal melanoma.
• Topical steroidal and non-steroidal eye medications may help relieve painful uveitis.

What is the prognosis for ocular melanoma?

Thankfully, with treatment, the prognosis for dogs with uveal melanoma is good. Most uveal melanomas are benign and the metastatic rate is very low. However, there is still the chance for local invasion and pain if left untreated.

And limbal melanoma is almost always benign and slow growing, so electing to monitor this tumor may be a safe option for your dog. Just keep in mind that any fast-growing mass should be quickly addressed to prevent damage to vision or eye structures.

Work with your vet to keep an “eye” on your dog’s eyes

As we discussed, some dog eye melanomas are easier to see than others. But it certainly doesn’t hurt to get into the habit of looking at your dog’s cornea, sclera, iris, and other visible eye structures on a regular basis. (To learn more about how to perform a weekly dog wellness scan, check out Dr. Buzby’s Tip-to-Tail Health Scan™ course). This routine health scan can be a great way to catch eye problems early on.

Plus, it is a good idea to take your puppy or adult dog to the vet for yearly wellness exams. And you should ideally bring your senior dog to the vet twice yearly for a checkup. These visits allow the vet to examine your dog’s eyes with the ophthalmoscope (and check the rest of your dog out too). Since some ocular melanomas aren’t visible to the naked eye, routine vet checks are a great way to detect melanoma before it starts causing problems.

Finally, if you or your vet find a potential eye melanoma, don’t lose hope. Follow your vet’s instructions (including pursuing a referral to a veterinary ophthalmologist if needed) and take it one step at a time. Chances are good that with careful monitoring or treatment, the melanoma won’t cause any long-term problems.

Did your dog have an eye melanoma?

Please share his or her story below.