Page 1251 - Problem-Based Feline Medicine

60 – THE CAT WITH ABNORMALITIES CONFINED TO THE CORNEA 1243

Classical signs—Cont’d the most common cause of corneal perforation, and there
may be other evidence of skin wounds from the fight.
● Collapsed anterior chamber with varying
degrees of hyphema (blood) and protein. The perforated corneal lesion is usually with a linear
● Iris prolapse may be seen as black bulge in wound or triangular tear that is plugged with fibrin
the wound. surrounded by a dense area of edema. The injured
● If the wound has not sealed and is leaking cornea may be covered with a layer of fibrin.
aqueous humor, there will appear to be The eye is held tightly closed, and cats with this injury
excessive amounts of tearing and the face will resist any handling of the eye.
will be wet.
There will be a serous discharge often tinged with
fresh blood.
Pathogenesis
The anterior chamber may be very shallow and the
Cat claw wounds are the most common cause of globe very soft.
corneal perforation.
If the wound has not sealed and is leaking aqueous
When the cornea is perforated the anterior chamber humor, the face will be wet and there will appear to be
collapses. If the wound is large enough, the iris comes excessive amounts of tearing.
forward to plug the defect causing an iris prolapse.
A black, bulging area in the wound is a sign of an iris
An immediate prostaglandin reaction is set up within prolapse. In lightly pigmented irises, the bulge may be
the eye, causing leakage of protein from the iris and brown in color.
ciliary body blood vessels.
Another sign of iris prolapse is a distorted pupil with
The sudden decompression of the globe causes hemor- the affected iris leaflet presenting towards the wound.
rhage in the anterior chamber. The hemorrhage may This can only be visualized if the anterior chamber is
also be caused by an injury to the iris by the penetrat- not filled with blood.
ing claw.
Cats that have a penetrating corneal lesion should be
The anterior lens capsule may be torn, causing lens examined carefully for signs of lens rupture. This
rupture. This causes a severe antigenic reaction to the can be very difficult to ascertain. An obvious tear in the
released lens proteins within the globe. anterior capsule may be seen in the pupil space if the
The wound is plugged by fibrin in cases where there is pupil is not miotic, and the anterior chamber is not very
no iris prolpase. This forms a platform for fibroblasts to cloudy or full of blood. Sometimes leakage of lens pro-
develop and the healing process in the wound is begun. tein seen as thick transparent jelly-like material can
be seen in the anterior chamber. However, if the tear in
Secondary complications are common with anterior the lens capsule is under a small wound in the periph-
synechia (adhesion of iris to cornea) and posterior eral iris, it may be impossible to see. In such cases,
synechia (adhesion of iris to anterior lens capsule). This watch for intense uveitis that will not respond to
causes distortion of the pupil (dyscoria). therapy. A cataract will form in the injured lens.
Secondary glaucoma may develop if the iridocorneal These cases need to be referred to a veterinary ophthal-
angle becomes obstructed. mologist whenever possible.
Cats with ruptured lenses are at risk for developing an Iris prolapse may be difficult to differentiate from
intra-ocular sarcoma (see The Cat With a Cloudy a descemetocele in cases that have a very painful eye.
Eye, page 1276).

Differential diagnosis
Clinical signs
Keratomalacia (melting ulcer).
Corneal perforations are severe corneal injuries that ● A very cloudy cornea with soft gelatinous stroma
present as ocular emergencies. Cat claw injuries are covering a large area.