Page 1307 - Problem-Based Feline Medicine

63 – THE CAT WITH ABNORMAL IRIS APPEARANCE 1299

and mydriatics can be used to push the iris away from
PENETRATING INJURIES TO THE IRIS**
the cornea.
Classical signs Partial iridectomy may be necessary if a prolapsed
section of iris is badly damaged or atonic.
● Corneal lacerations.
● Mis-shapen pupil margin and bulging of Intra-ocular surgery may be required to remove a dam-
iris tissue into the corneal defect. aged lens to prevent destruction of the eye by severe
● Visible iris tear. lens-induced intra-ocular inflammation. If the lens is
● Blood and fibrin in the anterior chamber. severely traumatized then eye ablation would be
recommended to reduce the possibility of later post-
traumatic intra-ocular sarcoma development.
Pathogenesis
IRIS ATROPHY**
Injuries to the iris usually occur in conjunction with
injuries to the adjacent cornea or sclera.
Classical signs
If the corneal injury is large, the iris may prolapse
● Loss of normal iris color and increased
through the cornea and plug the defect.
transparency of the iris in an old cat.
● Sluggish pupillary light reflex (PLR).
Clinical signs
Pathogenesis
Trauma to the eye may result in a variety of changes to
the iris including: Iris atrophy is an age-related atrophy and thinning of
● Visible iris tears. iris structures, especially the anterior stroma, pupil
● Iris prolapse through the corneal wound. margin and associated pupillary constrictor muscle.
A black, bulging membrane will be seen with asso-
ciated fibrin. The pupil margin is mis-shapen asso- Clinical signs
ciated with the iris moving forward into the corneal
Iris atrophy occurs in old cats, and appears as loss of
defect.
normal coloration and increased transparency of the
● Fibrinous adhesions to adjacent structures.
iris because of loss of pigment in the anterior iris
Fibrin and blood in the anterior chamber (hyphema) stroma. This may be especially obvious in old Siamese
are often present with trauma. cats or other color-dilute cats with blue irides. The iris
can become so thin that it may take on a transparent
Associated lens injury may occur, which may be dif-
appearance.
ficult to appreciate without removing fibrin from the
anterior chamber and dilating the pupil. There may be some loss of normal pupillary light
reflex (PLR) associated with atrophy of the pupillary
A penetrating foreign body may or may not be evident.
sphincter. In old cats with iris atrophy, pupil shape is
often retained, but the PLR is not as brisk as in
Diagnosis a younger cat. It is unusual to see atrophy to the degree
sometimes seen in old dogs, where notch-like defects
Diagnosis is based purely on the appearance of the iris occur, with thin connecting strands across the defect.
on careful examination.
If the pupil becomes very dilated, the equator of the
lens may become visible.
Treatment
Diagnosis
Surgical repair is recommended. This might include
replacement of iris tissue into the anterior chamber with Diagnosis is based principally on a consideration of age
suturing of the corneal defect. Viscoelastic substances and clinical signs.