What this means
The pupil is the dark circle in the middle of the eye that adjusts to light: it narrows in bright light and widens in the dark. Note whether both pupils are the same size, whether their shape is round, whether the iris, the coloured part of the eye, has a notch or gap, whether the pupils stay wide in bright light, and whether the eyes flash a bright reflection when you shine a lamp or take a photo with a flash.
Changes in the pupils can have very different causes. Some are inherited or form before birth, such as differences in how the iris is built. Others are linked to diseases of the retina, in which a dog gradually sees less, especially at dusk. Sometimes pupils widen because of a problem of the nervous system, a condition that needs urgent help, or the body's sensitivity to certain substances. The cause cannot be told from appearance.
A sudden change in the pupils, pupils of different sizes, or wide pupils together with other unusual signs need a vet the same day, since eye problems can quickly threaten sight. Do not put any drops in the eye or use home remedies. Your vet will find it useful to know when you noticed the change, whether your dog can see, whether both pupils match, whether it could have swallowed something, and, if you can, photographs of the eyes.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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A difference in how the iris formed
When the iris does not form completely, a notch or gap remains and the pupil looks an unusual shape. In bright light the dog may squint.
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A disease of the retina
When the retina gradually breaks down, a dog sees less, especially in the dark. The pupils may look wide and the eyes reflect light brightly.
About the condition: Progressive retinal atrophy (PRA) -
Body sensitivity to certain substances
Some dogs inherit a sensitivity to certain medicines, which can show as very wide pupils together with wobbling and trembling.
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Poisoning
Some substances widen or narrow the pupils. If your dog could have swallowed something, this must be said to a vet straight away.
About the condition: Poisoning -
A problem of the brain, nerves or pressure in the eye
Pupils of different sizes can point to a disease of the nervous system or of the eye. It needs an urgent examination.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether both pupils are the same size and round
- Whether a notch or gap can be seen in the iris
- Whether the pupils narrow in bright light
- Whether your dog sees less at dusk or bumps into things
- Whether the eyes reflect light brightly in lamp or flash light
- Whether there is also wobbling, trembling, heavy drooling or odd behaviour
When to book a routine visit
Changed pupils are worth showing to a vet, and a sudden change or pupils of different sizes need to be examined the same day, as eye problems can quickly threaten sight. Put nothing in the eyes.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Iris coloboma Eyes Iris coloboma is an inborn eye defect in which the iris, the coloured part of the eye, does not form completely and is left with a gap or notch. Because of this the pupil may look irregular in shape and cannot close down properly in bright light. The defect itself does not grow with age, but other changes in the eye can occur alongside it, so it is worth having the eyes checked by a vet.
- MDR1 gene mutation (multidrug sensitivity) General health This is an inherited change in a gene that makes some dogs unusually sensitive to certain drugs. That is why a vet should know that a dog has, or may have, this mutation before any medicine is used. A genetic test can show whether a dog carries it.
- Progressive retinal atrophy (PRA) Eyes Progressive retinal atrophy is a group of inherited eye diseases in which the cells of the retina slowly break down and the dog gradually loses its sight. The disease itself is not painful, but it can eventually lead to complete blindness. Genetic tests exist for some forms, so breeders can screen their breeding dogs.
Body systems: Eyes General health