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Chronic Superficial Keratitis (Pannus)

 

Chronic Superficial Keratitis (Pannus) is a disease seen most commonly in the German Shepherd, but does occur in other breeds. A progressive change occurs where blood vessels and scar tissue invade the cornea. This change usually begins in the temporal (outer) or ventral (lower) quadrant of the cornea, and severe cases can involve most or all of the corneal surface area resulting in blindness. With chronicity the affected areas become black with pigmentation.

It is believed that Pannus is an immune mediated disease. That is, some subcellular change has occurred in the cornea which the immune system then recognizes as abnormal resulting in an immune mediated attack in the cornea almost as if the cornea was foreign or transplanted tissue. It is suspected that the German Shepherd has a genetic predisposition to this disease, but the damage to the cornea which starts everything is thought to be associated with ultraviolet radiation. The first reports of cases of Pannus came from Austria and in the United States - from Colorado, both areas of higher elevation. Today, Pannus is diagnosed world wide, however it is well recognized that cases of pannus are more severe and harder to treat in areas of higher elevation, supporting the UV radiation theory. It is hypothesized that dissipation of the ozone layer has resulted in greater exposure to ultraviolet radiation.

It makes sense then to treat Pannus with medications that locally suppress the immune reaction. Steroids (such as dexamethasone and prednisolone) are anti-inflammatory medications which provide some immunosupression as a side effect. Cyclosporine, is a drug which has immunosupression as it's primary mode of action, and applied topically alone or in combination with steroids often results in better control of Pannus than the use of steroid alone.

Cyclosporine has been used by veterinary ophthalmologists in the treatment of pannus for 12 years now. A 1% or 2% solution is most often used, and was prepared in an oil base - usually olive, corn or vegetable oil. About five years ago a 0.2% cyclosporine ophthalmic ointment called Optimmune (Schering Plough) became available to all veterinary practitioners for the treatment of another eye disorder - keratoconjunctivitis sicca or dry eye - where it is quite effective. In pannus cases, however, I find the 0.2% ointment produces less success than the 1% solution. With treatment, the active vascularization and granulation tissue often resolves, but the scarring and pigmentation may improve somewhat slowly or not at all.

Recently, Sandoz has modified the formulation of the cyclosporine from which we make up the 1% or 2% solution. The newer formulation is called Cyclosporine Neoral, and it is a microemulsion. A microemulsion can be diluted into other solutions rather than oils. This is advantageous as the oil base of these mixtures would sometimes cause skin irritation around the eye, and could result in oil stains on the furniture if the dog rubbed its face on the sofa for example. The Cyclosporine Neoral microemulsion can be diluted into a bottle of dexamethasone or prednisolone eyedrops, simplifying the treatment regime. Initially some dogs find the newer formulation more irritating, but after a few weeks of treatment it is tolerated well. There are legal considerations to the use of unlicenced pharmaceuticals when a licenced product (Optimmune) is available on the market. If the use of cyclosporine is indicated, cases should be treated with Optimmune initially, and the use of unlicenced mixtures should be considered only if lack of response to treatment is noted on subsequent examinations.

A related condition where a similar immune mediated reaction is confined to the conjunctiva and the third eyelid is called PLASMOMA or Plasmacytic Lymphocytic Conjunctivitis of the third eyelid. This variation is also much more common in the German Shepherd. Compared to Pannus, plasmoma is less threatening to the vision, may cause more discomfort, and is somewhat more resistant to the treatment regime which is the same as for Pannus.

Reduction of exposure to ultraviolet radiation is also helpful in the longterm control of Pannus. Keeping the dog indoor during the sunniest part of the day; providing a doghouse shelter; or trying a specialty pair of canine sunglass goggles called Doggles may prove very helpful.

Since Pannus is an immune mediated disease, it is managed by treatment but not cured. Ongoing treatment for life is needed to maintain vision.