Understanding Feline Corneal Sequestrum
Feline corneal sequestrum is a localized death of corneal tissue. Unlike a standard corneal ulcer, which is an open wound, a sequestrum represents necrotic tissue that has hardened and turned dark brown or black. This condition is almost exclusive to cats and represents a significant departure from normal healing mechanisms.
The Mechanisms of Corneal Necrosis
The corneal stroma is highly sensitive. When chronic irritation occurs—whether from feline herpesvirus (FHV-1), entropion, or dry eye syndrome—the collagen fibers at the injury site may fail to regenerate. Instead, the area undergoes a mummification process, resulting in the characteristic black pigment. While researchers once suspected that Feline Ocular Sarcoma might develop from chronic inflammation, a sequestrum is fundamentally a non-neoplastic, albeit highly concerning, ocular lesion.
Clinical Manifestations and Symptom Recognition
Owners often notice the dark spot on their cat's eye long before the cat shows signs of systemic illness. However, the presence of the lesion is often preceded by ocular pain.
Acute vs. Chronic Signs
- Blepharospasm: Squinting or holding the eye shut is a classic sign of ocular pain.
- Epiphora: Excessive tearing or watery discharge.
- Corneal Pigmentation: The hallmark black or brown plaque located centrally or paracentrally.
- Neovascularization: New blood vessels growing from the edge of the cornea toward the sequestrum, signaling chronic inflammation.
Diagnostic Protocols in Veterinary Ophthalmology
Veterinarians diagnose this condition using a slit-lamp biomicroscope. A fluorescein dye test is frequently performed; however, the dye may not stain the center of the sequestrum because the tissue is dead and non-absorbent, even if the surrounding cornea is ulcerated.
Essential Diagnostic Steps
- Tonometry: Measuring intraocular pressure to rule out concurrent glaucoma, which can be mistaken for or complicate the lesion.
- Viral Testing: PCR testing for FHV-1, as viral reactivation is the most common underlying cause for persistent corneal defects in felines.
- Cytology: Sometimes performed if there is suspicion of secondary bacterial infection, which can mimic other systemic issues, similar to how Feline Cholangitis requires specific diagnostics for liver health.
Surgical Intervention and Therapeutic Approaches
While some sequestra resolve on their own, the wait-and-see approach is rarely recommended due to the high risk of secondary corneal rupture. Surgical intervention, typically a keratectomy, is the gold standard.
The Role of Keratectomy and Conjunctival Flaps
In a keratectomy, the surgeon removes the necrotic tissue. Once the sequestrum is excised, the resulting corneal defect is often covered with a conjunctival pedicle flap. This flap provides a rich blood supply to the area, acting as a biological bandage to promote healing and provide structural support. While recovery from surgery is generally successful, owners should be aware that systemic health must be maintained, as poor nutritional status or underlying diseases like Feline Hepatic Lipidosis can interfere with post-operative recovery.
