A systolic reading above 180 mmHg is the point where a cat's retina starts to come off the back of the eye, and it can happen within 24 to 72 hours of the pressure climbing. Vision loss is often the first sign anyone notices, so the pressure had been high for weeks or months. Three eye checks plus a Doppler reading catch it earlier, and a cat with a diagnosis is rechecked every 6 months for life.
Why 180 mmHg is the line
Systolic pressure in a healthy cat sits between 120 and 160 mmHg. A reading of 160 to 180 mmHg is the grey zone where white coat stress and true hypertension overlap, so it needs 2 or 3 visits. Above 180 mmHg sustained, the small vessels in the retina, kidney and heart start to leak, and above 200 mmHg the eye is at risk of detachment, haemorrhage or both. The retina in a cat is fed by vessels 0.1 to 0.2 mm across, and at that size a rise of 20 to 30 mmHg is enough to break the wall.
The damage is silent until it is not. Cats do not faint or complain; they adapt to a slow loss of vision by memorising the furniture, and owners usually report a cat that walks into doors after 3 weeks of nothing. Roughly 1 in 5 cats diagnosed with hypertension is already blind in at least 1 eye at the first examination.
Measuring it so the number means something
One reading is not a diagnosis. A Doppler session should produce 5 to 7 readings, the first 1 or 2 discarded, and the rest averaged. The cuff goes on the foreleg or the tail, sized to 30 to 40 percent of the limb circumference, and the cat rests in a quiet room for 5 to 10 minutes with minimal restraint. A full bladder, a recent blood draw and a barking dog in the next room each push the number up by 10 to 20 mmHg. If the first visit lands between 160 and 180 mmHg, the usual plan is 2 more visits 2 to 4 weeks apart before starting medication.
The three eye checks
- Fundoscopy. The pupil is dilated and the back of the eye examined for tortuous vessels, flame-shaped haemorrhage, pale patches of ischaemia and any area where the retina has lifted. This is the check that finds detachment before the cat is obviously blind.
- Pupillary light reflex. A bright light into each eye should produce a brisk constriction in under 1 second. A sluggish or absent reflex on one side points to retinal or optic nerve damage on that side.
- Menace response and vision. A hand moved toward the eye should produce a blink. A cat that does not blink but still navigates the room is using whiskers and memory, not sight.
Add tonometry while the cat is there: normal intraocular pressure is 15 to 25 mmHg, and a pressure over 30 mmHg after a bleed means secondary glaucoma that will cost the eye within days if it is not treated.
Readings that mean same-day action
| Test | Normal | Hypertensive change | Act within |
|---|---|---|---|
| Systolic pressure | 120 to 160 mmHg | over 180 mmHg sustained | 7 days |
| Fundus | flat retina, vessels 0.1 to 0.2 mm | detachment or haemorrhage | same day |
| Pupillary light reflex | constricts under 1 s, both eyes | sluggish or absent on 1 side | same day |
| Menace response | blinks both eyes | no blink on 1 or both sides | same day |
| Intraocular pressure | 15 to 25 mmHg | over 30 mmHg | 24 to 48 hours |
| Weight against 3 months ago | within 2 percent | down over 5 percent | 7 days |
Different laboratories and different tonometers set slightly different reference ranges, so compare a cat against its own previous readings as much as against the printed range.
What detachment looks like at home
The pupil goes wide and stays wide, often 2 to 3 times its normal size, and does not narrow in bright light. The cat misjudges the edge of the sofa, walks with its nose low, and stops jumping. In some cats a red haze or a visible blood clot sits behind the lens. The window for useful recovery is short: if pressure is controlled within 2 to 3 days, some cats regain 30 to 50 percent of vision over 4 to 8 weeks, and if the retina has been off for 2 weeks or more the loss is usually permanent. Hypertension is the single most common cause of sudden blindness in cats over 10, ahead of glaucoma and retinal degeneration.
Every 6 months, with the kidney and thyroid attached
Recheck every 6 months means pressure, fundus, weight, total T4 (reference 1.0 to 4.0 ug/dL), creatinine (0.9 to 2.5 mg/dL), SDMA (0 to 14 ug/dL), urine protein to creatinine ratio (under 0.4) and potassium (3.5 to 5.0 mEq/L). The three travel together: 20 to 60 percent of hypertensive cats have chronic kidney disease, and 10 to 15 percent are hyperthyroid. Treating a hyperthyroid cat can unmask hypertension 1 to 3 months later, because thyroid hormone keeps the vessels relaxed, so a pressure check belongs 4 to 8 weeks after starting medication and again at 3 months. A cat with kidney disease and high pressure is also a cat that often drinks less and ends up with hard stool, which is worth raising at the same visit as constipation risk.
Targets, drugs and the 14 day recheck
The treatment target is a systolic pressure under 160 mmHg, reached over 4 to 8 weeks rather than overnight, because a fast drop can cut blood flow to a kidney that has adapted to high pressure. Amlodipine is the usual first drug, at a dose the vet sets by weight and kidney function, with a second drug added if pressure stays over 180 mmHg. Recheck at 7 to 14 days after any change, then every 3 months once stable. A pressure that will not come down on 2 drugs is a reason to look again at thyroid and kidney values rather than to keep raising the dose.
Costs are modest next to a blind cat: a Doppler reading 20 to 50 USD, fundoscopy 50 to 120 USD, a senior blood panel 60 to 150 USD, and amlodipine 10 to 30 USD a month. Owners who track the annual total usually find the monitoring is a smaller line than the dental work.
Go today, not next week
Sudden blindness, a pupil that stays wide in daylight, blood inside the eye, a red or cloudy eye with pain, or any seizure in a cat over 10 needs a same-day visit. So does a systolic reading over 200 mmHg, even if the cat seems fine, because the retina can detach before the next appointment.
- Ask for a Doppler reading at the next senior visit, with 5 to 7 readings averaged.
- Have the fundus examined at the same appointment, not 6 months later.
- Test T4, creatinine and SDMA together, because the three conditions cluster.
- Recheck pressure 7 to 14 days after any drug change.
- Book the 6 month recheck on the day you leave the clinic.
Terms mentioned in this article
Frequently asked
Can a cat go blind from high blood pressure?
Yes, and it is the most common cause of sudden blindness in cats over 10. A sustained systolic pressure over 180 mmHg damages the retinal vessels, which are only 0.1 to 0.2 mm across, and the retina can detach within 24 to 72 hours. If pressure is controlled within 2 to 3 days, some cats recover 30 to 50 percent of vision over 4 to 8 weeks; after 2 weeks of detachment the loss is usually permanent.
How is blood pressure measured in a cat without stressing it?
A Doppler session in a quiet room, with 5 to 7 readings taken and the first 1 or 2 discarded, then the rest averaged. The cuff is sized to 30 to 40 percent of the limb circumference and the cat rests 5 to 10 minutes with minimal restraint. A full bladder or a dog in the next room can add 10 to 20 mmHg, so a borderline reading of 160 to 180 mmHg is repeated 2 to 4 weeks later.
Why does my hypertensive cat need thyroid and kidney tests?
Because the three conditions cluster. Roughly 20 to 60 percent of hypertensive cats have chronic kidney disease and 10 to 15 percent are hyperthyroid, so a pressure reading on its own misses the cause. Treating hyperthyroidism can also unmask hypertension 1 to 3 months later, since thyroid hormone keeps vessels dilated, which is why the recheck at 4 to 8 weeks matters.