Sudden Blindness in Cats: The 48-Hour Window

A cat that goes blind over a weekend has usually not lost its eyes. It has lost the retina to blood pressure, and how much vision comes back depends mostly on how fast that pressure is measured. If both pupils are wide open and stay wide open in a bright room, treat it as an emergency: get a systolic reading today, not next week.

The first sign is a pupil that will not close

In a normal cat, bright light pulls the pupil down to about 2 to 4 mm within 1 to 2 seconds. A cat with a detached retina keeps both pupils at 8 to 10 mm and they barely move when you shine a phone light from 30 cm. Owners read this as shock or fear. Fear does not survive 5 minutes of daylight.

Cats hide the rest well. They memorize the path from bed to litter box, lean on whiskers and paw pads, and quietly stop jumping onto the 1.2 m counter they used for years. Typical reports are 2 or 3 small things: a pause at the stairs, one shoulder clipped on a door frame, crying at 3 a.m. for no reason. By the time a cat walks into walls, the detachment is often 3 to 7 days old.

Blood pressure over 180 mmHg is the usual cause

Hypertensive retinopathy is the most common cause of acute blindness in older cats, and the damage is mechanical. Sustained systolic pressure above roughly 180 mmHg pushes fluid through retinal vessel walls, the retina lifts off the back of the eye, and photoreceptors lose their blood supply. Most of these detachments are bilateral, with the second eye following within days to weeks.

The eye is rarely the only organ hit. The same pressure damages the kidneys (proteinuria, rising creatinine) and thickens the left ventricle. In cats with hypertension, chronic kidney disease is the underlying cause in roughly 60 to 70 percent, hyperthyroidism in about 20 percent, and a smaller group has primary hypertension with no other disease found.

Systolic reading	What it means	Typical action	Recheck
120-150 mmHg	Normal	Screen every 6-12 months after age 8	6-12 months
150-160 mmHg	Borderline, white coat effect possible	Repeat 2-3 readings 2 weeks apart	2 weeks
160-180 mmHg	Hypertension, organ damage over months	Start amlodipine, treat kidney and thyroid	7-14 days
180-200 mmHg	Retinal detachment risk high	Treat today, examine both eyes	3-7 days
Above 200 mmHg	Emergency, detachment often present	Same-day treatment, hospital monitoring	24-72 hours

Why the 48-hour window decides the outcome

A detached retina is not dead tissue at hour 12. Photoreceptors survive on diffusion from the choroid for a while, then degenerate. The practical cutoff most veterinary ophthalmologists use is 48 to 72 hours for a real chance of useful vision. Cats treated inside 48 hours often regain some sight within 2 to 4 weeks. Retinas that have been off for 7 days or more usually leave light perception only, and some cats stay completely blind.

Treatment is not exotic. Amlodipine at 0.625 mg per cat once daily is the standard first step, raised to 1.25 mg if pressure is still above 160 mmHg at the 7 to 14 day recheck. The target is 120 to 160 mmHg. Dropping pressure faster than that cuts kidney perfusion, so most vets lower it over days rather than hours. Kidney and thyroid disease get treated at the same time, and the retina is re-examined every 2 to 4 weeks until it is flat or clearly stable.

Four tests you can run at home in 10 minutes

These do not replace an exam. They tell you whether to drive tonight.

1. Menace response. Move a flat hand toward the eye from 20 cm without touching whiskers or blowing air. A sighted cat blinks or pulls the head back. Do 3 trials per eye.
2. Cotton ball drop. Drop a cotton ball from 30 cm above and slightly to one side, then watch the eyes and head follow the fall. Repeat 3 times. A blind cat hears nothing, because cotton makes no sound.
3. Obstacle course. Place 3 chairs in a row, 30 to 40 cm apart, in a familiar room and watch from 2 m away. A sighted cat walks around them. A blind cat slows, pushes whiskers forward, or taps a chair leg.
4. Pupil light reflex. In a dim room, shine a phone light from 30 cm for 2 seconds per eye. Normal pupils shrink to 2 to 3 mm and hold that size while the light stays on.

What the vet checks on the first visit

Expect a full ophthalmic exam with a headlamp and indirect lens, pressure in both eyes, and 3 to 5 blood pressure readings taken before anything stressful happens in the room. Normal intraocular pressure is 15 to 25 mmHg. A reading over 25 mmHg with a cloudy cornea points to glaucoma instead of detachment, which is a different emergency with a 24 to 48 hour window of its own. Bloodwork usually includes a renal panel, T4, CBC, and a urine protein-to-creatinine ratio. On fundic exam a detached retina looks like a gray sheet with folds, while a normal tapetum reflects green-gold.

Other causes that look the same from across the room

Acute glaucoma (pressure 40 to 60 mmHg, painful, pupil mid-dilated, eye rock hard), uveitis, lens luxation, progressive retinal atrophy (slow, over 2 to 5 years, night vision goes first), taurine-deficiency retinal degeneration in cats on unbalanced homemade diets, brain disease, and poisoning. Household toxins that can cause blindness or seizures include permethrin spot-ons made for dogs, organophosphate flea products, and ethylene glycol at 2 to 3 tablespoons. Check the toxin list before assuming blood pressure is the whole story.

What to do in the next 60 minutes

• Pad the corners of the 2 or 3 tables the cat uses and put a board across the stairs.
• Leave the litter box, food, and water exactly where they were. Do not move furniture for 4 weeks.
• Call and say: both pupils fixed and dilated, sudden onset, cat is 12 years old. Ask for a blood pressure reading, not only an eye exam.
• Do not use leftover eye drops. A steroid drop on an ulcer can cost the eye in 48 hours.
• Bring every medication and flea product name, plus the dates you used them.

If the retina reattaches, vision may return in 2 to 6 weeks and it may be partial. If it does not, a blind cat in a stable home lives a normal-length life, and there is a practical guide to helping a blind cat settle in. Watery or crusty eyes after the event need a separate look, covered in eye discharge in cats.

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