Page 1211 - Problem-Based Feline Medicine

58 – THE CAT WITH A RED COLORATION OF THE GLOBE 1203

Clinical signs Thyroid function should be checked using thyroxine
(T4) concentrations. (See page 301, The Cat With Weight
Hypertension causes leakage of fluid and red blood
Loss and a Good appetite, for details of diagnosis).
cells into the retina, and rupture of retinal blood vessels.
Cardiac ultrasound may be used to confirm thyro-
Vitreal hemorrhage caused by hypertensive retinopa-
toxic cardiac hypertrophy.
thy appears as acute-onset vision loss in an old cat,
and is usually bilateral. The cat suddenly starts to bump
into things, appears to be lost, and has very cautious
movements. TRAUMATIC HYPHEMA*

The pupils are usually dilated, and non-responsive or
Classical signs
poorly responsive to light.
● Uniform red color is seen through the
Affected eyes appear slightly cloudy, and there may be
pupil.
focal red areas visible through the pupil.
● Pupil may be dilated.
It is difficult to visualize the retina on fundoscopic ● ± Hemorrhage in the anterior chamber.
examination, as it appears out of focus. This is caused ● Signs of trauma such as sub-conjunctival
by retinal detachment and the retina ballooning into hemorrhage and adnexal injuries.
the vitreous.
Hypertensive cats may have cardiomegaly and left Clinical signs
ventricular hypertrophy. There may be other signs
suggestive of hypertension such as a bounding cardiac Blunt or penetrating trauma may cause hemorrhage
apex beat. into the vitreous.
Systolic arterial blood pressure is usually greater than Hemorrhage in the vitreous appears as a uniform red
160 mmHg. color visible through the pupil. The eye may have
a red glow caused by free red blood cells in the vitre-
Other signs suggestive of chronic renal failure or
ous. Hemorrhage may also be present in the anterior
hyperthyroidism may be present, such as progressive
chamber.
weight loss, polydipsia, polyuria, azotemia, inappe-
tence or polyphasia, or a palpable thyroid nodule. The pupil may be dilated.
On ophthalmoscopic examination, no detail will be
visible in the fundus. The retina will not be able to be
Diagnosis visualized because of the intense red color of the vitre-
ous infiltrated with red blood cells.
Clinicians should suspect this problem in any old cat
that has suddenly gone blind. Other signs of trauma to the eye, such as conjuncti-
val and sub-conjunctival injury and hemorrhage, and
Ophthalmoscopy will demonstrate vitreal hemorrhage.
adnexal injuries may be present, or there is a history
The retina will be hard to focus showing hemorrhage
of trauma.
adjacent to the major retinal blood vessels.
Blood pressure is most commonly measured in cats using Diagnosis
Doppler technology. Arterial blood pressure greater than
160 mmHg confirms a diagnosis of hypertension. Most Diagnosis is based on the clinical signs of a red color
cats with clinical signs of retinopathy have a blood pres- visible through the pupil, and the reflection of the retina
sure of greater than 200 mmHg. and tapetal is obscured. There is usually a history of
trauma.
Blood urea nitrogen (BUN), creatinine and a urine
protein:creatinine ratio are useful clinical pathology Ocular ultrasound using a 10-Hz probe is a very
parameters to check renal function. useful adjunct to diagnosis. This will show problems