Sunken Eyes in Cats: 5% Dehydration and 24-Hour Plan

Eyes that sit deeper in the socket are the earliest visible sign of dehydration in a cat, and the threshold is low: about 5% of body weight in fluid, roughly 200 ml for a 4 kg cat, flattens the fat pad behind the eye. Run the skin tent, gum and urine tests first, then start replacing fluid.

Targets: a skin tent over 2 seconds, a third eyelid showing 2 mm or more, and a 24-hour replacement of 40-60 ml per kg plus the deficit. A cat that is dull, breathing fast or cold needs the clinic, not a bowl.

One fat pad, no spare room

The eye sits in a cone of fat, 7 extraocular muscles and thin bone. The retrobulbar fat pad gives up water first when the body is short, because it is not needed to stay alive. Lose 1% of body weight as fluid and a 4 kg cat is down 40 ml; at 5% it is down 200 ml and the eye drops back 1-3 mm, enough for the lid opening to look smaller. The coat is the other early signal: grooming stops and fur looks dull within 24-48 hours.

Three home tests that read 5%

Tent test: lift the skin between the shoulder blades and let go. Under 2 seconds is normal, 2-3 seconds is 5%, 3-4 seconds is 6-8%, and skin that stays folded is over 8% and a same-hour problem.

Gum test: press a fingertip on the gum above a canine until it blanches, then count to colour return. Under 1 second is normal, 1-2 seconds is marginal, over 2 seconds means poor perfusion rather than thirst. Gums that feel tacky instead of slick mean 5% or more. Urine test: small, dark, strong volumes, and 12 hours with no urine at all is an emergency. Dehydration and bladder inflammation often travel together, so read the urine findings against blood in cat urine.

Fluid loss	Skin tent at the shoulders	Eye and third eyelid	Gums	What to do
Under 5%	Under 2 s	Normal, no eyelid visible	Moist, pink	Fresh water, recheck in 12 h
About 5%	2-3 s	Slight sinking, 1 mm eyelid	Tacky, pink	Vet within 24 h
6-8%	3-4 s	Sunken, 2-3 mm eyelid	Dry, pale pink	Same day, fluids started
8-10%	4 s or longer	Deep set, 3-5 mm eyelid, dull cornea	Dry, CRT 2 s	Emergency now
Over 10%	Over 5 s, stays folded	Lids half closed, cornea dry	Cold, CRT over 2 s	Shock, IV route only

Read the 3 tests together: one abnormal result earns a 12-hour recheck, 2 earn a same-day visit.

Horner syndrome: the same look, a different cause

Horner syndrome produces the same picture, and water has nothing to do with it. Four signs travel together on one side: a pupil at 1-2 mm against 5-8 mm, an upper lid drooping 2-4 mm, the eye pulled back 2-3 mm, and the third eyelid up 3-5 mm.

The separating test is symmetry and the pupil. Dehydration is bilateral with equal, reactive pupils; Horner is unilateral in roughly 85-90% of cases and the small pupil stays small in dim light. Screen for middle ear disease (discharge, head tilt, a scratch behind the ear), neck or chest trauma in the past 1-7 days, a neck mass, and aminoglycoside ear drops.

Other reasons the eye looks deep

A retrobulbar abscess pushes the eye forward, but the swelling still distorts the lids; look for a fever of 39.5-40.5 C, pain when the mouth opens 1-2 cm, and a 24-48 hour course. Fat atrophy from weight loss does the opposite: the eye is truly deeper because the padding shrank, typical after a 200-400 g loss in an older cat, and fluid will not change it.

Pain and shock also do it. A cat in severe abdominal pain holds the eyes half closed with the third eyelid up, and shock from poisoning or a blocked bladder can cost 8-10% of body weight in 12-24 hours. If vomiting followed a plant or a human medicine, run it through the toxic plant and drug list rather than waiting for a slot. Sunken eyes plus 40+ breaths a minute is a separate emergency, covered under fast breathing in cats.

The 24-hour target, in millilitres

Maintenance is 40-60 ml per kg per day, and the deficit is 10 ml per kg for every 1% of body weight lost. A 4 kg cat at 8% needs 320 ml of deficit plus 160-240 ml of maintenance, so 480-560 ml over 24 hours.

Replace half the deficit in the first 6-8 hours and the rest over the next 16, with the oral route capped near 2-3 ml per kg per hour; faster in a vomiting cat produces more vomit and less fluid. Urine output should reach 1-2 ml per kg per hour, so 4-8 ml an hour in a 4 kg cat, within 6 hours of the first drink.

Route: a cat that eats and does not vomit takes 5-10 ml from a syringe every 30-60 minutes, 20-30 ml an hour. A cat that fights the syringe needs subcutaneous fluid at the clinic, 100-150 ml per site, 2 sites. Shock or a dull cornea means intravenous fluid.

What not to do

• Do not push 60 ml at once: a cat stomach holds about 20-30 ml per kg and returns the excess.
• Do not use human electrolyte drinks, which carry 30-50 mmol of sodium per litre and 5% sugar.
• Do not wait for the cat to drink: a cat at a 5-8% deficit takes in 10-20 ml a day.
• Do not give a diuretic or a human anti-vomiting drug.

When to see a vet

Go within the hour for sunken eyes with gums that stay pale after pressure, a cat that cannot stand, 40+ breaths a minute at rest, no urine for 12 hours, or more than 4 vomits in 12 hours. Same day for a tent of 3 seconds or more, a third eyelid covering 2 mm, or 24 hours without food. Within 48 hours for a 2-3 second tent, and for sinking on one side only, which needs a pupil and ear exam.

First 24 hours at home

1. Weigh the cat and calculate the deficit: kg x percent lost x 10 ml.
2. Run the 3 tests and write the seconds down as tomorrow's baseline.
3. Offer 5-10 ml every 30-60 minutes, 20-30 ml an hour.
4. Put a 200 ml bowl at every resting spot and change it every 12 hours.
5. Recheck the tent at 12 and 24 hours; no improvement means the clinic.

Terms mentioned in this article

MMCRT

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