What is pigmentary keratitis?
Pigmentary keratitis refers to brownish-black discoloration of the eye’s surface caused by the deposition of pigmented melanin granules. This condition is most common in brachycephalic (flat-faced) dogs, such as Pugs, Boxers, Bulldogs, and French Bulldogs. This is likely due to their facial conformation and genetic factors.
What causes pigmentary keratitis?
Pigmentary keratitis is caused by chronic irritation or inflammation of the eye. When this chronic inflammation occurs, melanin granules can be deposited within the deep layers of the cornea. Common causes of eye inflammation that can result in pigmentary keratitis include diseases of the eyelid, such as entropion (inwardly-rolled eyelid), ectropion (outwardly-rolled eyelid), abnormal eyelashes, or eyelid tumors. Any of these abnormalities can cause chronic trauma to the eye’s surface.
Pigmentary keratitis can also be associated with keratoconjunctivitis sicca (KCS) or dry eye. In these patients, poor tear production leads to chronic eye inflammation. Abnormal blink reflexes may be seen in affected dogs, as their inability to protect and lubricate the eye leads to chronic inflammation. Some dogs will have a history of chronic or repeated corneal ulcers due to other causes or a history of previous corneal surgeries.
In some cases, no underlying cause can be identified. In other cases, pigment continues to form even after the underlying cause has been addressed. These factors suggest a genetic component to this condition.
What are the clinical signs of pigmentary keratitis?
Dogs with pigmentary keratitis have visible pigment deposition within the cornea. The appearance of this pigmentation can vary from faint brown speckles to dense black patches that can obscure vision. Owners can often observe pigmentary keratitis under normal lighting conditions, however, some cases are only detected upon closer examination.
"The appearance of this pigmentation can vary from faint brown speckles to dense black patches that can obscure vision."
How is pigmentary keratitis diagnosed?
Pigmentary keratitis can typically be diagnosed by your veterinarian on a routine physical exam. Your veterinarian may use an ophthalmoscope (or another light source) to examine the cornea’s surface and assess for other concurrent eye issues.
Once pigmentary keratitis has been diagnosed, your veterinarian will begin diagnosing the condition’s underlying cause. Your veterinarian will closely examine your dog’s eye, eyelids, and eye reflexes to look for abnormalities that may irritate the eye’s surface. Your veterinarian may perform a Schirmer tear test to evaluate your dog’s tear production and a fluorescein stain to rule out corneal ulcers. In some cases, your veterinarian may refer your dog to an ophthalmologist for a more advanced work-up.
How is pigmentary keratitis treated?
Treatment for pigmentary keratitis is directed at the underlying cause. If the underlying cause of the inflammation can be identified and corrected, it may be possible to stop the deposition of additional pigment in the cornea.
Surgical correction is often required in the case of eyelid abnormalities, such as entropion, ectropion, eyelash abnormalities, or eyelid tumors. The surgical procedures used to manage eyelid abnormalities are designed to restore the normal eyelid contour and decrease further trauma to the cornea.
"Surgical correction is often required in the case of eyelid abnormalities, such as entropion, ectropion, eyelash abnormalities, or eyelid tumors."
In cases of KCS or dry eye, medications such as cyclosporine (Optimmune®) or tacrolimus are utilized to help encourage tear production. Artificial tear drops or ointments may also be used to lubricate the eye.
The pigmented areas are rarely removed surgically due to the risks associated with this surgery. Medications may be used in some cases, though results are variable.
In most cases, pigmentary keratitis cannot be fully reversed. The pigment may lighten over time, but it is uncommon for the pigmented deposits on the cornea to resolve fully. In cases of KCS, however, restoring an appropriate tear film may allow the discolorations to resolve completely.