Heterochromia (Irregular Iris Pigmentation) in Cats and Dogs

Overview of Heterochromia in Cats and Dogs

Heterochromia, also known as binocular heterochromia and heterochromia iridis, is a condition that results in irregular pigmentation of the iris. In layman terms, this condition results in two different colored eyes. The iris is the colored tissue in the front of the eye that surrounds the pupil and gives the eye its color. Humans commonly have blue, brown, green, or hazel irises. The function of the iris is to regulate the size of the pupil by allowing more or less light to enter the eye.

Iris pigmentation is typically uniform, though irregularities, like one eye being a different color or more than one color, occur with conditions like heterochromia. These irregularities can be present at birth or acquired later in life as a result of a variety of diseases.

• Congenital heterochromia. This condition can be present in cats, dogs, humans, horses, and other animals. In cats, it is most common in breeds like Persians, Japanese Bobtails, Khao Manee, Siamese, Ragdolls, Turkish Van, and Turkish Angoras. Dog breeds commonly affected include Australian Cattle Dogs, Australian Shepherds, Border Collies, Chihuahuas, Dachshunds, Dalmatians, Great Danes, Shetland Sheepdogs, Siberian Huskies, and Shih Tzu. It is caused by a genetic color dilution effect. Color differences result from variances in the quantity of pigment (melanin) present. Lack of pigment in part or the entire eye causes a blue or blue-white appearance. In these circumstances, heterochromia is considered a normal clinical finding.
• Acquired heterochromia. This can be caused by an injury or inflammation in the eye. Any age, breed, or sex may develop acquired heterochromia.

What to Watch For

Heterochromia appears as iris pigment variations in one eye or a difference from one eye to the other. Examples include an iris that is half brown and half blue, or one blue eye and one brown eye.

• Pets with congenital heterochromia have normal vision. In addition to this condition, there is an increased incidence of deafness in white cats and Dalmatians.
• Acquired heterochromia results from inflammation or an injury to the eye. An active problem may demonstrate clinical signs like:
  • Red inflamed conjunctiva
  • Excessive tearing or discharge
  • Pawing at the eye
  • Cloudy appearance to the eye
  • Sensitivity to light (squinting) or holding the eye shut

If your pet is showing new signs of heterochromia or has any abnormal symptoms, call your veterinarian or closet veterinary emergency clinic.

Diagnosis of Heterochromia in Cats and Dogs

Heterochromia is diagnosed by examination of the eye that shows pigment changes in the iris. If it’s congenital, it may be a coincidental finding during a routine examination. However, if it’s acquired, diagnostic tests are recommended to determine the underlying cause.

Tests may include:

• Examination of the eye with an ophthalmoscope, which can reveal signs of inflammation in the front (anterior chamber) of the eye, as well as other abnormalities.
• Measurement of intraocular pressure (IOP). This is used to diagnosis uveitis and glaucoma, which cause similar clinical signs (like inflammation). The IOP is a painless procedure that generally takes less than 5 minutes.
• A fluorescein stain test, which can reveal a corneal ulceration or abrasion. A pigmented eye drop is placed on the eye which adheres to the cornea in the presence of a superficial abrasion.
• An ultrasound.
• Blood tests, such as a feline leukemia and feline immunodeficiency virus test (cats), complete blood count (CBC), or serum biochemical profile (blood chemistry). These are used to evaluate for signs of underlying disease.

Treatment of Heterochromia in Cats and Dogs

In cases of congenital heterochromia, no treatment is needed. In cases of acquired heterochromia with active signs of inflammation or ulceration, treatment may include the following:

• Topical medications (drops or ointments) placed on the eye. Antibiotics, steroids, anti-inflammatory drugs, or a combination of drugs may be recommended.
• Oral medications for treatment of pain and inflammation.
• Specific therapies as appropriate (depending on the underlying cause). Possible treatments may include antibiotics, anti-fungal medication, or immune system-suppressing drugs to address immune-mediated inflammation.

Home Care

For pets with active inflammation, administer all medications as directed. For instructions on how to medicate the eye, please read How to Administer Eye Medication to Your Dog.

Monitor your pet closely for signs of worsening ocular pain or inflammation. Call your veterinarian immediately if you see changes or your pet is rubbing at the eye. Scratching, pawing, or rubbing can cause additional damage. An e-collar may be recommended.

Preventive Care

Prevention tips for developing acquired heterochromia include:

• Neutering and keeping cats indoors, which can minimize exposure to infectious diseases like feline leukemia virus or feline immunodeficiency virus that can cause uveitis. At risk cats may benefit from the feline leukemia vaccine.
• Minimize exposure to tickborne diseases by providing tick-control measures as recommended by your veterinarian based on your pet’s geographic location and risk factors. Examine your pet daily for attached ticks and remove them. For tips on how to remove ticks, click here.
• See your veterinarian for annual examinations, recommended vaccinations, fecal examinations, and deworming medications.

Prognosis for Dogs and Cats with Heterochromia

For dogs and cats with congenital heterochromia, the prognosis is excellent, as this is a normal clinical finding. The prognosis for acquired heterochromia depends on the underlying cause.