the development of an opaque, dark brown to black plaque on the cornea
What is it?
A corneal sequestrum is a dense, black spot on the cornea (the clear front part of the eye). This condition appears to be unique to cats.
What breeds are susceptible?
Corneal sequestration can occur in cats of all ages and breeds. The breed with the highest frequency of occurrence is the Persian breed. Other at-risk breeds include Siamese, Burmese and Himalayan.
What are the symptoms?
Besides the black spot on the cornea, this condition can be painful and may result in squinting, tearing, and elevation of the third eyelid.
What is the cause?
The exact cause is unknown, but the development of a sequestrum follows this sequence: A cat suffers trauma or infection of the cornea, resulting in a corneal ulcer (a defect in the surface layers of the cornea). Sometimes, for reasons that are not always understood, these corneal ulcers fail to heal and the ulcerative surface layers become sequestered from the healthy adjacent cornea and undergo cell death. Pigments in the tear film may accumulate in the affected tissue, coloring the ulcerated area black. This dark, discolored area is called a corneal sequestrum. A corneal sequestrum is thus an area of dead, discolored cornea.
How is it treated?
A sequestrum may eventually slough from the cornea after several months; alternatively, it may remain in the cornea and progress deeper through this tissue. Surgery is recommended if cats are painful or if the sequestrum persists for longer than a few months. The reason is that if a sequestrum is present for a long time, it may progress more deeply into the cornea. Removal of a deep sequestrum is more difficult than removal of a superficial one, and if it is very deep there is a risk of perforation of the eye. Following removal of the sequestrum, we recommend placing either a Biosis or conjunctival graft or a corneal transplant into the area where the sequestrum was removed.
What is the prognosis?
If a sequestrum is removed and the cornea left uncovered there is a significantly higher risk of the sequestrum recurring. Placement of a graft or corneal transplant helps to prevent recurrence of the sequestrum. The transplant or graft may not perfectly clear but will often become clearer over time.