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| Incidence
of Corneal Sequestrum by Breed |
| Himalayan |
35% |
| Persian |
35% |
| Siamese |
15% |
| Abbysinian |
5% |
| Domestic |
10% |
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| What is a sequestrum, anyway? |
To understand corneal
sequestrum ,
we first need knowledge of the anatomy of the cornea (clear portion of
the eye). Covering the outside of the cornea is a layer of epithelium.
This epithelium is much like our skin cells, but it usually isn't
pigmented and doesn't have hair or blood vessels in it. In the cat, the
epithelium is about 6-8 cell layers thick.
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Lining the inside of the
cornea is one cell layer called endothelium. These endothelial cells
are 'leaky' and allow fluid from the inside of the eye (aqueous humor)
to leak into the corneal tissue and then pumps it back into the front
of the eye. This pumping mechanism keeps the cornea clear. The greatest
portion of the thickness of the cornea (about 90%) is the 'stroma'
which is a collagen fiber matrix. The cornea in the cat is
approximately 0.6 mm thick. (For comparison, a dime is approximately 1
mm thick.) Corneal sequestrum is a condition peculiar to the cat in
which the corneal stroma dies and then degenerates. This condition is
called necrosis. The dead stroma becomes pigmented and becomes
irritating to the body causing pain and blood vessels to enter the
stroma. There is often corneal edema and white blood cell infiltration
as a 'foreign body' reaction to the necrotic tissue occurs. Various
names have been given to this lesion since it was first described in
1965. These include corneal mummification, the 'isolated black lesion',
corneal nigrum, keratitis nigrum, focal degeneration of the cornea,
corneal necrosis, primary necrotizing keratitis and corneal
sequestration or sequestrum. The cause of the corneal sequestrum is
unknown. A few veterinary ophthalmologists suggest primarily corneal
abnormal development. Other ophthalmologists suggest that the dead
tissue is secondary to a host of factors which cause corneal
irritation. Factors such as herpesvirus, lack of tear production
(keratoconjunctivitis sicca or KCS), chronic corneal ulceration and
foreign objects in the eye have all been suggested as causes of corneal
sequestrum. Additionally, some of these cats sleep with their eyes open
(lagophthalmos) , and the tear film is not spread adequately over the
central cornea which results in drying. Some affected cats have a
subtle inrolling of the lower eyelid (entropion) which may irritate the
cornea. The origin of the black discoloration of the necrotic stroma is
thought to be products in the tears which adsorbs into the degenerative
tissue. |
| 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.
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| Picture of the Week |
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| Super Fast
Fact |
The
Persian cat
is one of the most beautiful cats with a long, luxurious
coat. Owning a Persian gives one the same gratification as owning a
beautiful work of art.
Wild Cat
Here
are 36 species of wild
cats. |
| Useful Information |
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Domestic
Cat