Feline Hypertensive Retinopathy: Causes, Signs, Treatment

Feline hypertensive retinopathy is damage to the back of a cat's eye caused by high blood pressure. It can detach the retina and leave a cat suddenly blind, sometimes in both eyes at once.¹ A cat that suddenly bumps into furniture, or has wide pupils that stay wide in bright light, should be seen today.

What is hypertensive retinopathy in cats?

Hypertensive retinopathy is eye damage from blood pressure that stays high for a long time. The pressure strains the small vessels at the back of the eye. They stretch, leak or burst, which causes retinal swelling, pale patches and tiny hemorrhages. In severe cases the retina peels away from the back of the eye, and vision drops fast.^1,2

Vets measure the systolic pressure, the top number, in millimeters of mercury (mmHg). The American College of Veterinary Internal Medicine (ACVIM) groups cats by how likely the pressure is to damage organs:¹

Eye damage has been reported at pressures as low as 168 mmHg, and the risk climbs sharply above 180.¹ In one series of 69 cats with hypertensive retinopathy, 37 also had heart abnormalities and 20 had neurologic signs.³ The eyes are often the first clue.

Why high blood pressure stays hidden in cats

High blood pressure is usually silent until it injures an organ.¹ A cat can run high for months and look fine. A slight stumble, a new heart murmur or a subtle eye change often gets chalked up to aging.

We vets miss it too. Blood pressure isn't checked at every visit, and an anxious cat can read high only because of the visit. That's white coat hypertension, and it's why one reading isn't enough.¹

I try to check blood pressure in all my senior cats. The ACVIM suggests screening once a year from age 9, and cats with kidney disease or hyperthyroidism need regular checks at any age.^1,3 High pressure damages the kidneys as well as the eyes.¹

Common underlying diseases behind feline hypertensive retinopathy

When a cat develops hypertensive retinopathy, there's usually another disease driving the pressure up. The two I see most are:

• Chronic kidney disease. High blood pressure is common in cats with failing kidneys, and the pressure damages the kidneys further.¹ The symptoms of kidney disease in cats are covered in a separate post.
• Hyperthyroidism. An overactive thyroid raises the risk. The thyroid needs treating too, often with methimazole, but the blood pressure still needs its own treatment.¹

Less often, a hormone disorder is behind it: primary hyperaldosteronism, pheochromocytoma or Cushing's disease (hyperadrenocorticism).¹ Heart changes are common alongside high blood pressure, so a murmur in an older cat is a reason to check pressure.³

About 13 to 20 percent of cats have no identifiable cause. Vets call that idiopathic hypertension.¹

What symptoms may you notice if your cat has hypertensive retinopathy?

Early damage is quiet. Swelling and small hemorrhages at the back of the eye show up only on an eye exam, so a cat can look normal and still have retinal changes.²

When the retina detaches, the signs come fast: sudden blindness, wide pupils that don't shrink in bright light (mydriasis), bumping into furniture, or hesitation as your cat moves around the house.^1,2 Bleeding into the front of the eye (hyphema) makes it look red or cloudy.² Inflammation inside the eye (uveitis) causes redness and squinting. If the pressure inside the eye climbs (glaucoma), the eyeball can swell and look enlarged (buphthalmos).¹

Any of these needs a visit today.

How is this condition diagnosed?

I start with a full physical exam, because high blood pressure rarely hurts just one organ. I listen to the heart for murmurs, an irregular rhythm or a racing heart (tachycardia), and I look for neurologic signs such as stumbling (ataxia), seizures or odd behavior.^1,3

Next I measure blood pressure several times to rule out a stress spike. The ACVIM protocol is a quiet room, 5 to 10 minutes for the cat to settle, the owner present, and the average of 5 to 7 consistent readings after the first one is discarded.¹ A detailed eye exam follows. I'm looking for hemorrhages, retinal swelling and detachment.²

High blood pressure usually has a cause, so I also recommend blood work to check kidney, thyroid and liver values, plus a urine test.¹ Finding the cause shapes the treatment plan. For advanced damage I may refer you to a veterinary ophthalmologist, who can judge how severe the retinal damage is and guide treatment.

Treatment options for feline hypertensive retinopathy

The goal is to bring blood pressure down promptly and keep it there. That stops further retinal damage, and in some cats the retina reattaches.^1,2 The ACVIM goal is a systolic pressure under 140 mmHg, with 160 as the minimum target, and that's the range I aim for.¹ These are the drugs I use:

• Amlodipine (a calcium channel blocker) is my first choice, and the ACVIM's. Most cats start at 0.625 mg a day, and cats with a systolic pressure above 200 mmHg may start at 1.25 mg. It typically lowers systolic pressure by 28 to 55 mmHg, and side effects are uncommon.¹
• Telmisartan (an angiotensin receptor blocker) is a useful add-on to amlodipine, especially in cats with kidney disease and protein in the urine. The trial of telmisartan on its own left out cats with a systolic pressure above 200 mmHg or eye damage, so how well it works alone in those cats isn't known.¹
• ACE inhibitors such as benazepril or enalapril lower pressure only a little in cats. I add one to amlodipine when a second drug is needed, mostly in cats with kidney disease. They need kidney monitoring.¹
• Atenolol (a beta blocker) can slow a racing heart in some hyperthyroid cats. It barely lowers blood pressure, so it's never used alone.¹

If the eye has bleeding or inflammation, I add steroid eye drops.² If glaucoma develops, I prescribe drops to lower the pressure inside the eye. I avoid prostaglandin analogue drops because they can make inflammation worse.

What's next after starting treatment?

I recheck blood pressure within 7 days. If it hasn't reached the target, vets typically double the amlodipine dose.² Sometimes the pressure drops too low, which causes weakness or a fast heartbeat, and then I lower the dose right away.¹

A week or two later I repeat the eye exam to confirm the retina is stable and nothing new has bled or detached. Retinal swelling can improve within two weeks, and small hemorrhages can take one to two months to clear without scarring.² Eye checks continue through your cat's life, especially after a medication change.

ACE inhibitors and telmisartan can affect the kidneys, so I check kidney values with follow-up blood work.¹ Depending on the underlying cause, I'll also keep monitoring the thyroid or the kidney disease itself.

What is the overall prognosis?

Treatment can stop further damage, but sight generally returns in only a minority of cats.¹ The retina can reattach and the eye can look better without your cat seeing again, because reattached retinas are often degenerate.² In one series of 69 cats, amlodipine lowered blood pressure in 31 of 32 cats and improved the eye changes in 18 of 26.³

The outcome depends mostly on how long the retina has been detached and how fast the pressure comes down. Function recovers best when the detachment has been present for less than a week.² Early changes, before the retina detaches, can reverse with treatment.² A cat that is blind from detached retinas in both eyes when we first see her may not regain vision, even with the right treatment.²

Small hemorrhages often clear without scars. Heavy bleeding into the eye can pull the retina loose as the blood resolves, and an eye with that damage may never see again.²

Treating the underlying disease helps, but most pets stay hypertensive without medication, so rechecks and treatment usually continue.¹ I would rather catch high blood pressure on a routine check than after a cat loses her sight.

Have your senior cat's blood pressure checked once a year, and call us the same day if she suddenly can't see. We're at (519) 896-0532.