My rats eyes changed from black to completely red over a couple of days

My boys eyes were pitch black for his entire life. I adopted him so I don’t know his exact age but he is over 2 years old now so he is getting up there in age. Over the last two days they have turned this red and I’m freaking out. It is this red in all lighting as well. I have never seen this before and neither has the vet. They are going to stain the eyes and potentially prescribe eye drops. Has this happened to anyone else’s rats , any advice is greatly appreciated :/