What is pigmentary keratitis?
Pigmentary keratitis refers to a brownish-black discoloration of the surface of the eye, caused by the deposition of pigmented melanin granules.
Pigmentary keratitis is most common in brachycephalic dogs, such as Pugs, Boxers, Bulldogs, and French Bulldogs. This is likely due to their facial conformation, as well as 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 tumors of the eyelid. Any of these eyelid abnormalities can cause chronic trauma to the surface of the eye. Pigmentary keratitis can also be seen in association 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 properly 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, even after the underlying cause has been addressed, pigment continues to form. 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. Pigmentary keratitis can often be observed by owners under normal lighting conditions, however some cases are only detected upon closer examination.
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 other light source) to examine the surface of the cornea and assess for other concurrent eye issues.
Once pigmentary keratitis has been diagnosed, your veterinarian will begin the process of diagnosing the underlying cause of the condition. Your veterinarian will closely examine your dog’s eye, eyelids, and eye reflexes to look for abnormalities that may be irritating the surface of the eye. Your veterinarian may perform a Schirmer Tear Test to evaluate your dog’s tear production, as well as 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 of pigmentary keratitis is directed at treating 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 of the cornea.
In the case of eyelid abnormalities, such as entropion, ectropion, eyelash abnormalities, or eyelid tumors, surgical correction is often required. The surgical procedures used in the management of eyelid abnormalities are designed to restore the normal eyelid contour and decrease further trauma to the cornea.
"Treatment of pigmentary keratitis almost exclusively involves addressing the underlying cause for the chronic inflammation."
In cases of KCS or dry eye, medications are utilized to help encourage tear production. Artificial tears may also be used to aid in the lubrication of the eye.
The pigmented regions of the eye are rarely removed surgery, 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 fully resolve. In cases of KCS, however, restoring an appropriate tear film may allow the discolorations to completely resolve.