Pigment changes in your dog or cat’s eyes, which are common as they age, can be a normal variant or harmless change, but can also signal a serious underlying issue. The Veterinary Vision Center team uses advanced ophthalmic equipment and techniques to determine the source of your pet’s pigment change, and whether treatment is required. Here are the top reasons your pet’s eye could have a dark spot and how we treat these common changes.
#1: Pigmentary keratitis in dogs
Long-standing inflammation on the eye’s surface (i.e., keratitis) can result in dark, blotchy pigment deposition in dogs and can occur because of a breed predisposition, hairs that chronically rub on the eye, or eyes that are dry. Pugs are the most commonly affected breed, but any dog with a flat face and large eyes, such as a shih tzu or French bulldog, is also predisposed.
Pigment can be localized to a small area or can cover the entire cornea and obscure vision. Treatment in the earliest stages with eye drops to address dryness and inflammation can reverse pigment slightly, and may slow or prevent further pigment. The pigmented corneal layers can also be removed surgically, but the pigment almost always returns.
#2: Corneal sequestrum in cats
Cats commonly are infected with the feline herpes virus, which behaves similarly to the human cold sore virus—after initial infection, the virus becomes dormant in nerve cells and can reactivate during stress, or randomly throughout a cat’s life. The feline herpes virus causes eye inflammation and eye ulcers rather than cold sores, which sometimes leads to localized corneal tissue death and looks like a dark spot on the eye’s surface.
Over time, the sequestrum may push forward through the corneal layers and peel off on its own, but often surgery is required to remove this dead tissue. Topical antibiotics or antivirals are helpful if an ulcer is still active. If the cat is comfortable, with no squinting or excess tearing, playing the waiting game is a valid strategy, but surgery is recommended if the eye is painful.
#3: Uveal cysts in dogs
Uveal cysts are small, round, fluid-filled structures that appear as bubbles or dark spots in the front eye portion. These harmless cysts are common in several dog breeds, but in golden retrievers, they can signal the earliest stages of another disease called pigmentary uveitis. Cairn terriers with uveal or pigment changes often have a breed-specific condition known as ocular melanosis that can lead to glaucoma.
Most dogs with uveal cysts have otherwise healthy eyes and are perfectly comfortable. Cysts may be attached to the colored eye portion (i.e., iris) or may float and move around freely. Treatment is required only if many cysts are obscuring your pet’s vision, or a more serious underlying disease is suspected.
#4: Iris melanosis and melanoma in cats
Many cats who carry the piebald gene, which causes calico, orange, and tortoiseshell color patterns, are prone to freckles on their skin and mucous membranes. These freckles can also develop on the iris, and are especially noticeable on green eyes. Light-colored, flat-appearing spots in cats with this color pattern are typically nothing to worry about, and may continue to develop over time.
Some cats with dark spots on their iris actually have a cancerous condition called feline diffuse iris melanoma. Usually these spots are darker, more dense, and may look slightly raised on ophthalmic examination. Unfortunately, examination alone cannot definitively differentiate iris melanosis from early iris melanoma in cats, and biopsy is not possible without complete eye removal.
Melanoma can spread throughout the cat’s body, although often never does. Because of this uncertainty, treatment depends on how suspicious the lesions look, and level of owner concern. Eye removal and analysis provide a definitive answer, but many cat owners choose to monitor the lesions closely. Eventually, melanoma will lead to inflammation and possible glaucoma, which are easily detected on examination.
#5: Ocular melanoma in dogs
Melanoma can also occur in a dog’s eye, but instead of a diffuse lesion in the iris, these are well-defined, dark brown tumors that usually start near or behind the iris. As they grow, they may peek out from behind the iris, and extend out through the sclera or into the back of the eye.
While these tumors continue to grow larger and can damage the eye structures, they typically remain contained inside the eye and do not threaten a dog’s overall health. If the tumor is not causing any pain and your dog can still see with the eye, we may recommend close monitoring, but will recommend eye removal if the eye becomes painful or blind or the tumor begins to grow rapidly.
Eye pigment changes are rarely an emergency, but you should check in with your primary veterinarian as soon as you notice a problem, so they can rule out an active ulceration, infection, glaucoma, or other urgent eye condition. For definitive diagnosis and a treatment plan for eye pigment changes, or other eye issues, schedule a visit with the Veterinary Vision Center team.
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