Feline Hypertension: The Silent Cause of Sudden Blindness in Cats

Feline hypertension rarely announces itself. A cat with dangerously high blood pressure usually eats normally, plays normally, and shows no outward sign of distress — right up until the moment a blood vessel in the eye bursts, or the retina detaches, and a previously sighted cat is suddenly, permanently blind. It's one of the only common feline conditions where the first symptom owners notice is often the worst possible outcome. The good news is that it's also one of the easiest conditions to screen for with a single painless test, and one of the most reliably treatable once caught.

What Feline Hypertension Actually Is

Blood pressure is the force blood exerts against the walls of the arteries as the heart pumps it around the body. In cats, a systolic reading above roughly 160 mmHg is considered elevated, and above 180 mmHg is classed as a level with a high risk of organ damage. Unlike in people, feline hypertension is almost never a standalone problem — it is overwhelmingly secondary, meaning it develops as a consequence of another disease rather than appearing on its own. That's the single most important thing to understand about it: a hypertension diagnosis is really a prompt to go looking for what's driving it.

What Causes It

• Chronic kidney disease (CKD). The kidneys help regulate blood pressure directly, and failing kidneys frequently push it upward. A large share of cats diagnosed with hypertension also have some degree of CKD — see our guide to chronic kidney disease for how the two conditions interact.
• Hyperthyroidism. An overactive thyroid revs up the whole cardiovascular system, and a meaningful share of hyperthyroid cats develop hypertension as a result — one of several reasons a thyroid panel and a blood pressure check are usually run together. Our hyperthyroidism guide covers the underlying disease.
• Primary (idiopathic) hypertension. A smaller number of cats, usually older ones, have high blood pressure with no identifiable underlying disease at all — a true "essential" hypertension similar to the most common form in humans.
• Other, rarer drivers include obesity, certain adrenal gland tumours, and diabetes, though these are far less common triggers than kidney disease and thyroid disease.

Why It's So Easy to Miss

High blood pressure causes damage silently for months or years before an owner notices anything wrong, because a cat's everyday behaviour — eating, grooming, using the litter box — doesn't obviously change. It typically comes to light in one of two ways: it's picked up incidentally during a senior wellness screen, or it announces itself catastrophically once one of the organs it damages finally fails. The organs most at risk are nicknamed the "target organs," and each has its own warning signs:

• Eyes. By far the most dramatic presentation. Sustained high pressure can cause bleeding inside the eye, retinal swelling, or full retinal detachment — and a detached retina causes sudden, often total blindness that can happen within hours. Dilated pupils that don't constrict properly in bright light are an early clue.
• Kidneys. Hypertension accelerates kidney damage, creating a vicious cycle where each condition worsens the other.
• Heart. Chronically elevated pressure forces the heart to work harder, thickening the heart muscle in a way that can mimic or worsen hypertrophic cardiomyopathy — see our HCM guide for more on that overlap.
• Brain. Less common, but severe hypertension can cause disorientation, seizures, or other neurological signs from bleeding or swelling in the brain.

A vet explains what feline hypertension is, why it's usually secondary to another disease, and how it's treated.

How Vets Diagnose It

Blood pressure is measured the same non-invasive way it is in a human doctor's office, just scaled down: a small cuff wraps around a front leg or the base of the tail, and a Doppler probe or an oscillometric machine reads the pressure as the cuff inflates and deflates. It's painless and takes only a few minutes, though getting an accurate reading takes patience — a stressed, wriggling cat in a carrier will read artificially high (vets call this "situational" or "white-coat" hypertension), so most clinics take several readings in a calm environment before acting on the result, and some recommend letting the cat settle in the room for a few minutes first.

A demonstration of how a vet team measures blood pressure in a cat using a cuff and Doppler probe.

Because hypertension is so often secondary, a diagnosis doesn't stop at the cuff. Expect bloodwork to check kidney values and thyroid hormone, a urine test, and often a look at the back of the eye (the retina) to check for existing damage. Any cat over about seven or eight is a reasonable candidate for opportunistic screening at a routine check-up, even with no symptoms at all — it's exactly the kind of silent problem regular senior bloodwork exists to catch, alongside the other "big three" senior conditions covered in our senior cat care guide.

Treatment

• Amlodipine is the standard first-line medication — a once-daily calcium channel blocker that relaxes blood vessel walls and is generally very well tolerated by cats, often bringing pressure under control within a couple of weeks.
• Treating the underlying disease matters just as much as the blood pressure medication itself. Managing CKD or resolving hyperthyroidism (via medication, diet, or radioactive iodine treatment) often allows blood pressure to improve alongside it.
• Regular rechecks are non-negotiable, since the right dose can change over time as kidney function or thyroid status shifts. Most cats need a blood pressure check every few months once stable, more often just after starting treatment.
• Vision is not always recoverable. If a retina has already detached, rapid treatment sometimes allows partial reattachment and some vision to return, especially if caught within a day or two — but blindness from advanced, longstanding damage is usually permanent. This is the whole argument for screening before symptoms appear rather than after.

What Owners Can Watch For

Because early hypertension has no reliable home signs, vigilance is really about two things: keeping up with senior wellness visits, and reacting immediately if you do see something. Signs that warrant a same-day vet visit include:

• Sudden disorientation or bumping into furniture, especially in a previously confident cat
• Pupils that stay widely dilated even in bright light, or pupils of different sizes
• Visible blood or an obviously abnormal colour inside the eye
• Sudden reluctance to jump onto familiar surfaces, which can reflect either vision loss or discomfort
• New disorientation, wobbliness, or a head tilt

None of these are exclusive to hypertension, but all of them deserve prompt attention rather than a wait-and-see approach — the window to save vision, in particular, can be measured in hours to days rather than weeks.

The Bottom Line

Feline hypertension is common in older cats, almost always tied to another underlying condition, and dangerous largely because it gives so little warning before it damages the eyes, kidneys, heart, or brain. The test that catches it is quick, painless, and increasingly a standard part of senior wellness screening — which is exactly why it belongs on the checklist for any cat past middle age, symptomatic or not. Caught early and treated with daily medication, most cats do very well; caught only after a sudden blindness episode, the damage is often permanent. A blood pressure cuff is a small thing to add to a vet visit for how much it can prevent.