Corneal Sequestrum: a five minute read

                 

                     

                Corneal sequestrum is a rare condition of cats, and is also known as superficial focal necrosis, corneal nigrum, and partial corneal mummification among other colloquial names. It is clinically characterized by necrosis of the corneal stroma and presence of signs such as blepharospasm, epiphora and eventually photophobia, accompanied by the presence of an irregular, dark brown or black spot of variable size, localized most of the times in the center of the cornea. As with any necrotic tissue in the body, vascularization is observed surrounding the plaque.

       The cause is unknown, but previous corneal ulceration, eyelid malformation, or feline herpesvirus type 1 (FHV-1) infection may be predisposing factors. Persian cats appear to be the most affected, followed by Himalayan, Siamese and the Domestic Shorthair. These cats may be more vulnerable because of their facial conformation and natural exophthalmos. Clinically, the condition presents with a darkened lesion overlying layers of ulcerated or non-ulcerated cornea. In mild cases, the corneal epithelium remains intact, and the lesion appears light amber but in more advanced cases, the cornea can become black after the epithelium sloughs off. The necrotic tissue can extend from the corneal stroma to Descemet's membrane.

  The sequestrum is composed of desiccated and degenerated stroma. Histopathologically, it is characterized by the presence of necrosis of the stromal lamellae, and the black or brown color is due to desiccation rather than the presence of melanin or hemosiderin. This coagulative stromal necrosis varies in depth, causing a disconnection of the lamellae which favors spontaneous loosening.

Microphotograph of the normal cornea vs Corneal sequestrum

        Cats with corneal sequestrum are typically presented with epiphora, blepharospasm, ocular discharge, elevation of the nictitating membrane, corneal neovascularization, chemosis, hyperemia and Corneal edema around the lesion, all of which can be appreciated in the above picture.

    Medical management is supportive and may include topical antibiotics, atropine, lubricants, and antiviral agents (2). Superficial sequestra may eventually loosen and slough; however, the time to sloughing is variable and may extend for months to years. Corticosteroids should not be used for sequestra.

    Surgical management of corneal sequestra is the treatment of choice. Keratectomy to remove the sequestra relieves discomfort and may prevent extension of the lesion into deeper layers of the cornea but carries the risk of globe penetration if the deeper layers of the stroma are also involved.  Keratectomy may or may not be followed by various grafting procedures including conjunctival grafts, or corneo-conjunctival transposition.