Vetnuus | December 2025 41 Since this month is themed cats and dogs, we shall discuss a prevalent and important cat eye condition that causes both owners and vets grief, namely Corneal Sequestrum. Definition: Corneal sequestrae are common lesions seen in cats. A similar type of lesion is rarely described in dogs and horses. The sequestrum is characterised by a brown discolouration of the corneal stroma. In addition to the term sequestrum, this condition has also been referred to as corneal mummification, corneal nigrum, and corneal necrosis. Causes: The exact cause is unknown, but there seems to be an association with Feline herpesvirus Type 1 infections. Other known causes include corneal ulceration, traumatic corneal lesions and chronic corneal abrasion & irritation, as seen in cases of entropion in cats. Predisposed breeds: Although a sequestrum can occur in any cat breed, we certainly encounter them more often in brachycephalic breeds such as Persians and Himalayans. Other breeds commonly affected include Burmese, Siamese, Sphinx and the Oriental breeds. It is not unusual for a Maine Coon to have a lower lid entropion with associated developing sequestrum. The condition occurs in cats of all ages, with the apparent exception of neonates, and exhibits no gender predilection. Reported ages range from 5 months to 18 years with a mean age of 5.2–5.6 years. Pathogenesis and Clinical Appearance: The exact etiopathogenesis of sequestrum formation remains unknown. It is widely accepted that some form of chronic corneal insult needs to occur to initiate the process. Early reports speculate causes to include apoptosis and ultrastructural changes in keratocytes, which include clumping and margination of chromatin and shrunken cytoplasm, a local metabolic defect, a hereditary basis in colourpoint breeds, or a primary stromal dystrophy. The host of different brachycephalic breed-related adnexal abnormalities (brachycephalic ocular syndrome or BOS), including macroblepharon, lagophthalmos, entropion, and medial canthal trichiasis, are repetitively linked with corneal sequestration. Corneal sensitivity, particularly that of the central cornea, is known to be poorer in healthy Persians than in healthy DSH cats, but no statistical difference was found in the central corneal sensitivity of normal Persians versus those with sequestrae. Conjunctival goblet cell atrophy and an accelerated tear film break-up time [TFBUT] have also been presented as a potential cause of corneal sequestrae. There appears to be a possible correlation between decreased goblet cell/epithelial cell ratios in the conjunctiva and an accelerated TFBUT. Tear film dysfunction remains an emerging focus of investigation in this and other ocular surface diseases. A slight but statistically insignificant increase in tear protein concentration occurs in affected cats. Total tear lipid content appears significantly lower in affected eyes than in control eyes when evaluated with high-performance liquid chromatography. Iatrogenic sequestration has been reported following debridement or grid keratotomy of non-healing corneal ulcers. A sequestrum developed in 10% of eyes following debridement alone and 31% of eyes treated by grid keratotomy. It is for this reason that we do not perform a striate keratotomy in cats. Chemical cauterisation has also been incriminated as an iatrogenic stimulus. Despite all these potential causes, FHV-1 is still strongly implicated as a factor in sequestrum formation. Chronic corneal ulceration frequently precedes sequestration in many cats, and the most common cause of feline corneal ulceration is FHV-1 unless proven otherwise. FHV-1 DNA has been identified in experimentally induced and naturally occurring sequestra. Historically, it was hypothesised that upregulation of pro-inflammatory cytokines following keratocyte infection could explain the similarity in histologic features between a sequestrum and the collagen damage seen in herpes-induced stromal keratitis. Interestingly, the prevalence of FHV-1 DNA is greater in sequestra from domestic breeds than in Persians, lending support to the fundamental role of conformation in sequestrum formation in the brachycephalic breeds of cat. Regulars I Ophthalmology Column Corneal Sequestrum Dr Anthony Goodhead Specialist Veterinary Ophthalmologist Johannesburg and Cape Animal Eye Hospitals www.animaleyehospital.co.za Early sequestrum is seen as a light brown, tan area on the cornea
RkJQdWJsaXNoZXIy OTc5MDU=