Page 1298 - Problem-Based Feline Medicine

1290 PART 15 CAT WITH EYE PROBLEMS

be differentiated from keratic precipitates (KPs), The best-described degeneration occurs in the Abys-
formed as a result of anterior uveitis. A strand of tissue sinian cat. In this breed, both autosomal dominant
attaching the opacity to the iris, and the absence of other rod–cone dysplasia (onset 2–3 months of age), and auto-
signs of anterior uveitis is diagnostic of a persistent somal recessive rod–cone degeneration (onset 1–2 years
pupillary membrane. of age) modes of inheritance have been described. The
disease in Abyssinians is now seen rarely.
Treatment
No treatment is indicated.
Clinical signs
Typically there is a history of progressive vision loss.
IRIS COLOBOMA
Slow loss of pupillary light reflexes progresses to
Classical signs dilated pupils non-responsive to light.
● Wedge-like or radial sectorial defect in the Occasionally other signs, such as variable or intermit-
iris. tent nystagmus, are seen, especially in the rod–cone
dysplasia in Abyssinian kittens.
Clinical signs In the adult-onset form, the fundoscopic signs start as
a subtle grayish discoloration in the central retina on
Wedge-like or radial sectorial defect in the iris.
each side of the optic nerve head. The lesion progresses
Occurs as a congenital anomaly, but can be first to a more diffuse gray tapetal discoloration with early
noticed in a cat of any age. retinal vessel attenuation. Later, hyper-reflective areas
start to appear within the discolored tapetum. Finally,
The defect may enable structures behind the iris, for
there is extensive tapetal hyper-reflectivity with severe
example the lens equator or lens zonules, to be visual-
attenuation of retinal vessels.
ized more readily in the affected sector.
In the early-onset form there is tapetal fundus dull-
Diagnosis ness and loss of detail evident at 8–12 weeks of age.
Progression of the disease is fairly rapid, with develop-
The condition is quite rare in cats, and should be dif-
ment of tapetal hyper-reflectivity, loss of pigmentation
ferentiated from iris atrophy seen in old color-dilute
in the non-tapetum and vessel attenuation. There is
(Himalayan or Siamese) type cats.
end-stage degeneration by 12 months of age.
HEREDITARY PROGRESSIVE RETINAL
PHOTORECEPTOR DYSPLASIA OR Diagnosis
DEGENERATION
Diagnosis is based on the history of a slow onset of
vision loss, with slow deterioration of the pupillary
Classical signs
light reflex and characteristic fundoscopic changes in
● Progressive vision loss especially in a an Abyssinian cat.
young Abyssinian cat.
Diagnosis can be confirmed by demonstration of pro-
● Slow loss of pupillary light reflexes.
gressive reductions in b-wave amplitude on electro-
● Fundoscopic signs of tapetal hyper-
retinography.
reflectivity and retinal vessel attenuation.
Pathogenesis Differential diagnosis
Although rare, genetically determined progressive Other retinal diseases can usually be differentiated by
retinal rod–cone degeneration has been described in age and breed of the cat, other systemic signs and the
Abyssinian, Siamese and Persian cats. fundoscopic changes.