Rule # 1: Remember systemic hypertension is common in older cats
Rule # 2: Assume hypertension is the cause of vision loss until proven otherwise
Rule # 3: Check Blood (not eye) Pressure (BP)- if you can’t measure blood pressure refer patient to someone who can
Rule # 4: Blindness can be prevented or reversed in these patients if treated early
While there can be other causes of vision loss in older cats, hypertension is the most prevalent cause in our experience. Neurological causes are uncommon.
Sustained undetected high blood pressure leads to damage, leakage and rupture of blood vessels in vascular intraocular structures such as the iris and chorioretina. With the iris this can manifest as iris ‘bruises’, or more obvious large anterior chamber blood clots blocking vision. With the chorioretina, blood vessel leakage and rupture can lead to exudative retinal detachments and retinal haemorrhages, resulting in vision loss. If detached and deprived of normal nutrition for too long the retina will suffer permanent damage leading to permanent blindness. Early diagnosis and treatment are important for preserving and improving vision.
Once daily oral Amlodipine starting at 1.25mg/cat should be started immediately to preserve and maybe return some vision, regardless of any underlying disease.
Most cases of high blood pressure in cats appear to be age-related without a clear-cut primary cause. There is often some accompanying renal disease, secondary to hypertension, but renal disease can be the primary cause. Hyperthyroidism and other systemic diseases should be ruled out as causes of secondary hypertension with appropriate tests.
Any primary triggering disease such as hyperthyroidism will require additional specific treatment. The prognosis for vision is guarded but prompt diagnosis and ongoing timely anti-hypertensive treatment gives the best chance of haemorrhages clearing, retinas reattaching and some vision returning.
Should your clinic be routinely checking blood pressure in cats over 12 years of age?
Hypertension Trivia
- One in five cats older than 11 years will have hypertension
- It isn’t easy measuring BP: Consistent practice is required for reliable results, but if you don’t practice you will never get there
- Never treat solely on a single high BP reading unless there are also clinical signs consistent with hypertension e.g., anterior chamber haemorrhages
- The prognosis for cats with hypertension is good when diagnosed early
