Dear Doctor, Yesterday I noticed that my older cat's eye is changing color. It has become very dark at the bottom of his right eye, his eye's used to be yellow and now are a gold to brownish color. I don't have a good feeling about this, he already has hyper-thyrodism. This cat was a stray and we have no idea how old he really is, one vets best guess was 7-10 years old 6 years ago. Thank you for any info you can give.