Page 1177 - Problem-Based Feline Medicine

57 – THE BLIND CAT OR CAT WITH RETINAL DISEASE 1169

INFLAMMATION/INFECTIOUS:
Viral:
● Feline infectious peritonitis virus (p 1179)
Typically presents as young cats (7–9 months) with anterior uveitis. It may progress to blindness
with retinal detachment and/or central blindness and neurological signs. Other systemic signs
develop as the disease becomes chronic, such as weight loss, inappetence, lethargy and fever.
Fungal:
● Cryptococcus neoformans* (p 1174)
Blindness may be central in origin or caused by extensive chorioretinitis and retinal detachment.
Cats with this presentation usually have multi-organ disease.

Protozoal:
● Toxoplasma gondii* (p 1172)
These cats may have anterior uveitis, chorioretinitis and optic neuritis. Cats with CNS disease may
have central blindness and neurological signs.

transformation occurs in cells known as rods and cones.
INTRODUCTION
These cells form the outer layer of the neural retina.
The cones are used for day vision and color, and the
MECHANISM?
rods for night vision and movement. Cats have rod-
The ocular media are the transparent parts of the eye, dominated retinas. The rods and cones are supported
through which light passes to the retina. They consist metabolically by the retinal pigment epithelium,
of the cornea, anterior chamber, lens and vitreous. Any which lies internally to the choroid (vascular tunic of the
mechanism that causes loss of clarity in these media eye).
will cause loss of vision.
The rods and cones communicate with bipolar, hori-
● Corneal diseases that cause loss of transparency
zontal, amacrine and Mueller cells in the inner nuclear
will affect vision, and are described in the chapter
layer of the retina. These cells modify and integrate
“The Cat With Diseases Confined to the Cornea”
the stimulus produced in the rods and cones and trans-
(page 1233).
fer this information to the ganglion cells, which lie in
● A cloudy anterior chamber may affect vision. This
the inner retina. Axons from ganglion cells join to
is usually seen in cases that have uveitis (inflamma-
form the optic nerve.
tion of the vascular coat of the eye). Problems that
cause a cloudy anterior chamber are discussed in the Information from the rods and cones is thus passed via
chapter “The Cat With a Cloudy Eye” (page 1254). the inner nuclear layer cells and ganglion cells, to the
● Hemorrhage in the anterior chamber will cause visual cortex, where it is processed as vision.
vision loss. This is called hyphema and is discussed
The most common cause of blindness in cats is sec-
in the chapter “The Cat With a Red Eye” (page 1196).
ondary to problems associated with this complex tissue
● A cloudy lens is called a cataract and will cause
and includes:
vision loss. See the chapter “The Cat With a Cloudy
● Genetic disorders that effect metabolism of the
Eye” (page 1254).
rods and cones such as progressive retinal atrophy
● Inflammation or hemorrhage in the vitreous will
in the Abyssinian cat.
cause a vision defect. See the chapter “The Cat
● Metabolic toxins and deficiencies may cause
With a Cloudy Eye” (page 1254) or “The Cat With
retinal cell death. Examples include toxic retinal
a Red Eye” (page 1191).
degeneration, and taurine deficiency retinopathy.
The retina is complex neural tissue that transforms ● Systemic fungal, protozoal, viral, bacterial and
photic energy into electrical energy. This energy neoplastic conditions pass through the retinal pigment