I was just going to post about Iris Melanoma after a search.
Please don't panic - just see if you can get a referral to a feline eye specialist.
From the article I found:
For the full article, click here.
Examination involves the use of a slit-lamp biomicroscope, which determines whether or not the tumor is cancerous. If the pigmented area on the iris is flat, the lesion is referred to as an Ins Melanosis. This is considered to be pre-cancerous and is rechecked at six-month intervals.
"You can say any foolish thing to a dog, and the dog will give you a look that says, 'Wow, you're right! I never would've thought of that!'" -- Dave Barry