Uneven pupils in kitten

Hello everyone,
I am fostering five kittens at the moment. The smallest one, I call "Mouse" has uneven pupils. I've attached a photo.
He's quite tiny, but eating, drinking, climbing, playing, purrs etc etc.
I know head injuries can cause this as well as tumors etc. His behavious doesn't indicate any underlying illness that's obvious.
Has anyone had a cat/kitten with uneven pupils but healthy otherwise?
I doubt the shelter will want to pay for a vet visit unless he's exhibiting symptoms. He has to go eventually (3 weeks) to get a pre adoptive check up anyway.
Thoughts?

Uneven pupils is not a good thing. This kitten needs to see a vet as soon as possible.

Just doing a search online... you need to get this kitten to vet, stat

"There are a couple of causes for uneven pupils. One is Uveitis, an inflammation of the eye. It can cause the pupil in the affected eye to be smaller. Medical treatment of Uveitis must be aggressive to prevent glaucoma, the scarring of the structures inside the eye and possible blindness. Another cause is Horner's Syndrome. This is a neurological disorder that makes the pupil of the affected eye smaller. Feline leukemia can also cause a difference in size of the pupils. Watch out also for Toxoplasmosis. This parasitic protozoa can affect the eyes and the central nervous system and can produce inflammation of the retina, abnormal pupil size (and even blindness, poor coordination, personality changes, circling, head pressing, ear twitching, seizures, difficulty in chewing and swallowing food, seizures, and loss of control over urination and defecation functions, etc..)."

You really should take him to the vet

I've asked the staff at the shelter and they don't feel it's necessary if he is not having any symptoms.
The vet is only going to say one of two things: 1. wait and see if he starts to have symptoms of a brain tumor or other neurological signs or 2. they will want to do tests.
The kitten will be euthanized before spending money on tests.
So, I really don't see a point in taking him.
If he remains symptom free, a vet will give a pre adoption check up, at which time he will prob advise whether he is adoptable or not.
I WILL intervene if they choose euthanasia.
I was just hoping someone has seen this before and that this could be a defect or hereditary.