What is pigmentary keratopathy?

A diagram of the normal canine eye courtesy of Dr. Carrie Breaux

The cornea is the transparent structure at the front of the eye that allows light to pass into the eye.  A normal, healthy cornea is clear.  “Keratopathy” is disease of the cornea.  Pigmentation of the cornea occurs when the normally transparent cells of the cornea become pigmented, or brown.  “Pigmentary keratopathy” describes the process of the cornea losing its normal transparency by the cells taking on brown pigment.  This disease was formerly known as "pigmentary keratitis" but has since been renamed to "pigmentary keratopathy".

Having pigmentary keratopathy is analogous to having large amounts of mud on the windshield of your car.  Just a few flecks of mud may not impair your vision, but if your entire windshield (or cornea) is covered in mud (or pigment), then you may be functionally blind.  Pigmentary keratitis is common in pugs and other brachycephalic breeds.  The cause of the progressive pigmentation is unknown at this time.

Clinical Photos of Pigmentary Keratopathy

A normal pug's eye has a clear cornea with no pigmentation to impair vision.  Note that the cornea is crystal-clear with no pigmentation, scarring or blood vessels, allowing the inside of the eye to be easily visualized.

This pug is very mildly affected with pigmentary keratopathy.  Note the swirling pigment (brown discoloration) and fibrosis (grey discoloration).  Pigmentary keratopathy usually begins at the inside (medial) aspect of the cornea and progresses towards the center of the cornea.

This pug is mildly affected with pigmentary keratopathy.

This pug is mildly affected with pigmentary keratopathy.

This pug has moderate pigmentary keratopathy.  Note that the pigment extends further towards the center of the cornea, causing more visual impairment than pigment that does not extend this far.  The pupil has been dilated using eye drops in this photo, causing the tapetal reflection (light bouncing off the inside of the eye) to give the pupil a blue-green glow.  This tapetal reflection is normal. 

This pug is moderate to severely affected with pigmentary keratopathy.  Note the increased density of pigment, extent of pigment towards the center of the cornea, and the decreased ability to visualize the pupil.

This pug is severely affected by pigmentary keratopathy.  Note the extremely dense pigment and that visualization of the inside of the eye is almost impossible.  This pug is likely very significantly visually impaired.

This pug is severely affected by pigmentary keratopathy.  Note the density of the pigment and the difficulty in visualizing the inside of the eye.  The white reflection on the left side of the photo is a reflection of the photographer's hand.  This pug is likely significantly visually impaired.

There is no treatment that can reverse pigmentary keratopathy completely.  Once pigment has covered the cornea, it is very difficult to remove.  Two eyedrops have been used to help prevent the spread of pigment and decrease the amount of pigment on the cornea: cyclosporine A (CSA) and tacrolimus.  Both of these medications are immunomodulators, which means they influence the way the immune system behaves on the surface of the eye.  It is unknown how these medications change the pigmentation of the cornea.  Generally, use of these medications will be lifelong.  If the medications are stopped, the pigmentation will likely continue to get worse.  An additional benefit of these medications is that they are used to treat dry eye (also known as keratoconjunctivitis sicca, or KCS).  Some older pugs may have dry eye that can make their pigmentary keratopathy worse; these medications will help with both the dry eye and the pigmentary keratopathy.

Other medications that may be prescribed for pigmentary keratopathy include steroids, such as dexamethasone or prednisolone.  Steroids act to suppress the immune system by a different mechanism than CSA or tacrolimus.  Since steroids are very potent in their suppression of the immune system, their use may be associated with devastating infection on the surface of the eye.  Steroid medications can also be administered by injection into the conjunctiva (white surface) of the eye.

Surgical removal of the pigment is generally not effective long term since the pigment tends to recur quickly.  Surgical alteration of the eyelids to prevent the inside corner of the lower eyelid from rubbing on the surface of the eye may slow the progression of pigmentary keratitis.  Such surgical techniques include medial canthoplasty, transection of the medial canthal ligament and modified Hotz-Celsus.  

One of the goals of the Pigmentary Keratopathy in Pugs research team is to find a way to prevent and treat pigmentary keratopathy.