Are dilated pupils in a cat an emergency?

Treat persistently dilated pupils in an older cat as urgent, particularly if the cat is bumping into things, hesitant on stairs, or the pupils do not shrink in bright light. Retinal detachment from hypertension can sometimes be reversed if blood pressure is lowered quickly, and the window is measured in days.

How do I know if my cat has gone blind?

Cats compensate remarkably well in familiar surroundings, so blindness is often missed. Look for bumping into furniture that has been moved, hesitancy on stairs or jumping down, walking with the head low, startling when approached, and pupils that stay wide regardless of light.

What bloodwork is run for a cat with dilated pupils?

Blood pressure measurement first, then bloodwork looking for the underlying cause: creatinine, urea and SDMA for kidney disease, and total T4 for hyperthyroidism. Those two conditions account for most feline hypertension, and both are treatable.

Cat Dilated Pupils: When It's High Blood Pressure

Q: Why are my cat's pupils dilated all the time?

Pupils that stay wide in bright light are not normal. In an older cat the most important cause to rule out is systemic hypertension, where high blood pressure damages the retina and can detach it. Acute blindness is the most common clinical sign of hypertension in cats, and fixed dilated pupils are frequently what brings owners in. Other causes include pain, fear, certain medications, eye disease and neurological problems.

Q: What causes high blood pressure in cats?

In cats, the most common causes are kidney disease and hyperthyroidism. That is why a cat presenting with sudden blindness or dilated pupils gets bloodwork rather than just an eye examination — the eye is showing the consequence, and the cause is usually elsewhere.

A cat's pupils widen in the dark, during play, when startled and when excited — all entirely normal. What is not normal is pupils that stay wide in good light, or that do not narrow when you turn a lamp on. In an older cat, that specific finding has one cause worth ruling out before any other.

The Cause That Makes This Urgent

Systemic hypertension — high blood pressure — damages the small vessels at the back of the eye. Cats develop retinal haemorrhage, swelling, tortuous vessels and, in the worst cases, a detached retina. The pupil dilates because the eye is no longer receiving light properly, and it stops responding.

Acute blindness is the most common clinical sign of systemic hypertension in cats. Fixed, widely dilated pupils and blood in the front of the eye are frequently the reason an owner brings the cat in at all — the hypertension itself produced nothing they could see until it reached the eye.

The reason this is time-critical rather than merely serious: a recently detached retina can sometimes reattach and vision can return, if blood pressure is brought down quickly enough. Left for a week or two, that possibility closes.

Why the Cause Is Usually Not the Eye

In cats, the most common causes of hypertension are kidney disease and hyperthyroidism. Both are common in older cats and both are treatable, which is the encouraging part of an otherwise alarming presentation.

It also explains why a cat that arrives with an eye problem leaves with a blood test. The eye is displaying a consequence; the cause sits in the kidneys or the thyroid, and treating the eye without finding it achieves nothing.

The Other Reasons Pupils Dilate

Pain or fear — a cat in pain often has wide pupils, so this can be the first hint that something hurts.
Medications — several drugs dilate pupils as a side effect. Worth reviewing anything started recently.
Eye disease itself — glaucoma, uveitis, lens luxation and retinal degeneration.
Neurological problems — anything affecting the nerves controlling the iris. One-sided dilation especially points here.
Taurine deficiency — rare in cats on complete commercial diets, but a consideration in home-prepared or vegetarian feeding.

One Pupil or Two?

Worth noticing, because it narrows things considerably. Both pupils dilated together suggests a systemic cause — blood pressure, a drug, generalised retinal disease. One pupil dilated and the other normal, called anisocoria, points at something affecting that eye or its nerve supply specifically, and is its own reason to be seen promptly.

How to Tell If a Cat Has Lost Vision

Cats hide blindness well, because a familiar home can be navigated from memory. The signs are subtle: hesitating before jumping down, feeling for stairs, walking with the head lower than usual, startling when approached from the side, and bumping into anything that has been moved. Owners frequently discover it only after rearranging furniture. If you suspect it, move a chair and watch.

What the Vet Will Check

Blood pressure first, then a look at the back of the eye, then bloodwork for the underlying cause. That means creatinine, urea and SDMA for kidney function, and total T4 for thyroid status. Hypertension is managed with medication, but controlling whichever disease is driving it is what keeps it controlled.

Kidney or thyroid results back?

Upload your cat's panel and see creatinine, SDMA and T4 explained in plain English — the values behind most feline high blood pressure.

Check My Cat's Results

Frequently Asked Questions

Why are my cat's pupils dilated all the time?

Pupils that stay wide in bright light are abnormal. In an older cat, hypertension damaging the retina is the priority to rule out. Pain, medications, eye disease and neurological problems also cause it.

Is it an emergency?

Treat it as urgent in an older cat, especially with any sign of vision loss. Retinal detachment can sometimes be reversed if blood pressure is lowered quickly.

What causes high blood pressure in cats?

Most often kidney disease or hyperthyroidism. Both are common in older cats and both are treatable.

One dilated pupil, not both?

Called anisocoria. It points at that specific eye or its nerve supply rather than at a systemic cause, and should be seen promptly.

How can I tell if my cat is blind?

Move a piece of furniture and watch. Cats navigate familiar rooms from memory, so bumping into something newly moved is often the first real evidence.