Ocular Melanosis in Dogs

Aqueous humor is continuously being produced in the eye.  This fluid is beneficial to the eye in order to keep its shape, provide the ocular tissues with nutrients and protects against dust, wind and pathogens. The abnormal deposits of melanocytes clog the trabecular meshwork, which is unable to drain the buildup of aqueous fluid.  The trabecular meshwork is responsible for normally draining the aqueous humor from the eye. When the eye is unable to drain the aqueous humor, the increased fluid causes pressure under the eye.  The increased fluid inside the eye results in secondary glaucoma. Ocular melanosis is also known as pigmentary glaucoma.  

Ocular melanosis is an inherited condition found in Cairn Terriers and is occasionally observed in other breeds such as Boxers and Labrador Retrievers. The condition usually occurs in dogs 5 to 11 years of age.  The disorder usually affects both eyes. Dogs diagnosed with ocular melanosis should not be bred.

If your dog is showing symptoms of ocular melanosis, he should be seen by a veterinarian as soon as possible.  This is a painful condition that potentially can lead to partial loss of vision or blindness.

Ocular melanosis in dogs is an eye condition which causes an increase of melanocytes in the iris (the eye color), choroid (the vascular layer of the eye) and the sclera (the white of the eye).  Melanocyte cells produce melanin, the substance that gives pigment (color) to our skin, hair and eyes. The accumulation of melanocytes in the eye clogs the drainage of aqueous humor.

Symptoms may include:

• Anterior uveitis - inflammation
• Pigment particles can be seen in the eye

Symptoms of secondary glaucoma may include:

• Blood shot eyes
• Cloudy cornea
• Pain
• Enlarged/bulging eyes
• Watery discharge
• Excessive tearing
• Sensitive to light
• Decreased appetite
• Dog is withdrawn and does not want to play because of pain

Ocular melanosis in dogs is a congenital inherited condition which causes melanocytes to block the drainage of aqueous humor. The specific mutated gene has not been identified. Ocular melanosis is present at birth but clinical signs usually do not appear until the dog is older.

The veterinary ophthalmologist will want to go over your pet’s medical history. He will want to know the symptoms you have noticed and the timeline of when they started. The veterinarian will examine the patient’s eyes. The ocular exam will be done in the light and then in a darken room to see the reaction in the pupil and the cornea. The veterinarian may perform a pupillary light reflex test using a penlight.  The dazzle reflex test checks the eye’s involuntary response to intense lighting (blinking, third eye protrusion).  

If the veterinarian suspects glaucoma he may want to measure the intraocular pressure using a computerized handheld device.  He may also want to perform a gonioscopy, which helps to evaluate the drainage system in the eye.  Your dog will need to be sedated for this test. To rule out ocular tumors, the veterinarian may suggest skull x-rays.

There is no cure for ocular melanosis in dogs. The veterinarian may recommend starting the patient on topical anti-inflammatory medications. Analgesics may be prescribed to control the pain associated with secondary glaucoma. In addition, medications that decrease fluid production may also be prescribed. There are laser surgical procedures to help reduce the formation of aqueous humor such as cyclophotocoagulation. The veterinarian may recommend the implantation of a shunt (gonioimplantation). The gonioimplantation may assist with the drainage of aqueous humor, which will relieve pressure in the eye.

The pressure caused by secondary glaucoma can damage the nerve fibers of the optic nerve causing partial loss of vision.  The optic nerve is responsible for sending images to the brain, which is how the dog can see.  If the optic nerve is destroyed due to glaucoma, the patient will become blind. The damage to the optic nerve caused by the buildup of pressure is permanent. It is important to prevent the buildup of fluid under the eye.

Dogs that are not responding to the glaucoma treatment plan may need to undergo the removal of the eye. This will relieve the pain and discomfort. Your dog will adapt to his new circumstances and will learn to depend on his remaining keen senses. If the eye is removed, a prosthetic ball is then placed in the orbit and the eyelid is sutured closed.

Patients being treated for secondary glaucoma will need to be closely monitored.  Frequent eye exams will be necessary to measure intraocular pressure and to make sure the patient is responding to the medication. Additionally, dogs with glaucoma should be walked on a harness, not with a neck collar or choker.  The pulling on the neck can put pressure on the jugular vein, which may trigger intraocular pressure to rise.

Owners of canines that undergo a surgical procedure will be given postoperative instructions from the ophthalmologist surgeon. The dog will be sent home with a cone so that he does not scratch at the incisions and/or eyes.  Follow up visits will be required to remove sutures and to monitor the patient’s recovery.