Funny eye

Does anyone know about eyes? I have 2 buns that are fine and healthy, thank goodness. However, in my local pets at home they have a bunny up for adoption. He has one eye that looks different. It looks like the pupil has leaked into the rest of his eye, so the black bit is not round The other eye appears normal. The bunny in question is very laid back- I held him and checked teeth, bum, feet etc and he didn't struggle. He may be slightly overweight, but the eye is bothering me a bit. I wouldn't want to adopt him if it was indicative of something serious like a brain tumour-would rather someone with expertise with poorly bunnies took him on. If anyone can tell me what to look out for that would be great as I will go back tomorrow and have another look.
He's in PAH Wokingham if anyone is local- called Bugsy- white with black stripe. I will try to take a photo tomorrow. Also, if anyone has any experience with adopting from PAH, would be great if they can pass on any tips. Apart from the size of the cage, they appear to be taking good care of him. The member of staff let him run around on the floor, but I don't think this is a regular occurrence.
Thanks in advance.
Claire

I know that in humans an irregular pupil can just be a genetic trait. Could be the same in bunnies if he seems fine otherwise.