Corneal Sequestrum

Cats

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A corneal sequestrum is a darkly pigmented area in the cornea of the cat often associated with chronic ulcerative or inflammatory diseases of the cornea. This dark brown spot is an area of dead corneal tissue, and it may be surrounded by inflammation, blood vessels, and edema of the cornea.

A corneal sequestrum can cause chronic irritation and ulceration of the eye resulting in discomfort. Scar formation after resolution of the sequestrum may result in decreased vision. In rare cases, it may result in perforation of the eye with possible loss of vision. It usually involves one eye, although it may occur in both eyes at the same time.

Causes

  • A sequestrum can form as a result of chronic irritation and exposure of the cornea. Predisposing causes include abnormal eyelid conformation with eyelashes or hair rubbing against the cornea, inadequate tear production, corneal ulceration, and corneal infections.

  • Prior infection of the cornea with feline herpesvirus may predispose a cat to developing a corneal sequestrum.

  • Certain breeds of cats are predisposed to this disorder, including the Persian, Himalayan, and Burmese, but all types of cats may be affected.

    What to Watch For

  • Chronic squinting
  • Chronic brown or yellow-green eye discharge
  • Appearance of a black spot on the cornea (the clear part of the eye)
  • Cloudiness or redness of the eye
  • Rubbing the eye

    Diagnostic Tests

  • Thorough examination of the eye and the eyelids
  • Fluorescein staining of the eye
  • Schirmer tear test
  • Corneal scrapings for culture and detection of herpesvirus infection

    Treatment

    Corneal sequestra may be treated by two methods: with medications alone or with medications and surgery.

  • Medications alone. This method is used in those cats that do not exhibit any pain, and in which the sequestrum lesion is small and not causing much corneal inflammation. Medications include antibiotic eye ointment or solutions three to four times a day and possibly atropine ointment to improve comfort when needed. Antiviral medications are considered if an active infection with herpesvirus is suspected.

  • Medications and surgery. The removal of the sequestrum is preferred when the sequestrum is causing the cat to be painful, when the lesion is large and disrupting the surface of the cornea, or when it is causing significant inflammation of the cornea. Medications may also be used. Some cats that have had corneal sequestra require life-long medications with topical lubricant ointments to try and protect their corneas, and prevent recurrence of the condition.

    Home Care and Prevention

    Give all medications as directed. Call your veterinarian if you are having difficulty medicating your pet.

    Observe your cat for rubbing of the eye. An Elizabethan collar may be necessary to prevent further irritation of the eye.

    A warm compress applied to the eye may soothe the eye and help remove the discharge that is commonly present. Return your cat to your veterinarian if the discomfort appears to get worse.

    In some cases, use of an artificial tear ointment applied to the eyes twice a day may help to prevent recurrence of the sequestrum.

    Periodic rechecks are required to monitor corneal sequestra treated with medical therapy alone. If the lesions fail to resolve with medication, surgery may be needed. Following surgery, frequent rechecks are indicated until the cornea has healed.

  • Several eye diseases may look similar to a corneal sequestrum, but treatment of those diseases is usually very different from the treatment of a corneal sequestrum. Establishing the correct diagnosis is therefore very important. Diseases that may appear similar to corneal sequestration include:

  • Corneal ulceration. A corneal ulcer is an abrasion on the surface of the cornea or a break in the surface that appears as an indentation in the cornea. There is no brown discoloration associated with an uncomplicated corneal ulcer. The eye is red and painful and should be treated by a veterinarian as soon as possible. Corneal ulceration can occur along with corneal sequestration.

  • Corneal foreign body. Tiny pieces of plant material or wood can adhere to the surface of the cornea and resemble the black appearance of a corneal sequestrum. These foreign bodies should be removed as quickly as possible.

  • Corneal pigmentation. The cornea can become pigmented secondary to chronic irritation. In the cat, corneal pigmentation is a very rare event. In the case of simple corneal pigmentation, the underlying cornea is still living, healthy tissue. In a sequestrum, the involved piece of cornea has died.

  • Iris cyst. Iris cysts are also very rare in cats. These are dark brown fluid-filled structures that form inside the eye near the pupil. They may burst in the eye and coat the inside of the cornea with pigment. This may resemble the brown color seen in a sequestrum. Iris cysts are generally harmless.

  • Adhesions between the iris and cornea. After severe injury to the cornea, adhesions may form between the iris (the colored part of the eye) and the cornea during the healing process. These adhesions may become permanent and leave brown spots in the cornea.

  • Corneal scar. After an injury to the cornea, the resulting scar tissue may sometimes accumulate harmless pigment, although this is much more common in the dog than it is in the cat.

  • Corneal perforation. This is a very serious condition that requires immediate attention. In the case of a corneal perforation, a hole is present in the cornea, exposing the inside structures of the eye to the outside environment. The risk of infection is high and the eye may lose vision. When a hole is present in the cornea, the iris often comes forward to fill the defect, resembling the black appearance of a sequestrum. Fluid may be present on the cheek.

  • Veterinary care should include diagnostic tests and subsequent treatment recommendations.

    Diagnosis In-depth

  • Your veterinarian will perform a thorough examination of the eye and structures around the eye. Careful examination of the cornea under magnification is necessary to identify adhesions between iris and cornea, to diagnose harmless pigmentation, or to recognize a corneal scar. Examination of the structures within the eye may reveal the presence of an iris cyst. The eyelids are examined for foreign bodies, abnormal eyelashes and the position of the eyelids needs to be evaluated. In some cats, entropion (inward rolling of the eyelids) may cause chronic irritation of the cornea with secondary sequestrum formation. In cats that are severely painful, application of a topical anesthetic solution allows better examination of the eye.

  • Fluorescein stain is applied to the eye to determine if corneal ulceration is present. An ulcer may or may not be present in the area of the sequestrum.

  • The tear production is measured using a Schirmer tear test to check for inadequate tear production (dry eye).

  • A test for feline herpesvirus (IFA or PCR) may be performed.

  • Your veterinarian may recommend referral to a veterinary ophthalmologist for further evaluation and treatment.

    Treatment In-depth

    There are two general methods of treating a corneal sequestrum. One method employs the body's ability to reject dead tissue while protecting the eye with medication. The other method is surgical removal of the diseased tissue.

    Medical Management

    The eye is treated with an antibiotic solution or ointment three to four times a day. Atropine ointment is sometimes used to relieve pain when the pupil has become very small and spastic, but it may, in some cats, cause severe drooling. This effect is more commonly seen with atropine drops than with atropine ointment.

    Medical management allows the body time to remove the sequestrum. The purpose of the medication is to prevent secondary bacterial infections while the body removes the sequestrum. Blood vessels will grow into the cornea and will eventually grow under the sequestrum and remove the sequestrum from the cornea. This entire process may take many months to complete.

    Surgical Management

    Surgical treatment consists of careful removal of the affected layers of the cornea. In some cats, the sequestrum involves both superficial and deep layers of the cornea, making conjunctival or corneal grafting procedures necessary after removal of the lesion. Aftercare consists of topical antibiotic solution of ointment, with or without atropine, for a few weeks while the surgery site heals. The advantage of surgery is quicker resolution of the problem and return of the cat to a pain-free state.

    A sequestrum may recur after it has either been allowed to slough using medical management or after it has been surgically removed. There is some evidence that suggests that recurrence is less likely if the entire lesion is surgically removed, and all abnormal tissue is successfully removed from the cornea.

  • If your veterinarian has placed an Elizabethan collar on your cat, please keep it on at all times. A few unobserved seconds without eye protection are enough for your cat to irritate, scratch or rub the eye.

  • You can clean the eye gently using a warm compress such a cotton ball with warm water to remove any discharge if necessary. You should do this prior to application of medications.

  • Return your cat to your veterinarian for a re-evaluation if the discharge changes character or if the eye appears to be more uncomfortable over time.

  • If an underlying cause for the sequestrum was detected, this should be treated to prevent a recurrence of the sequestrum.

  • Use of an artificial tear ointment twice a day in affected cats, or in cats predisposed to corneal sequestration, may reduce the chance of recurrence.

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