This may be a benign condition called an iris cyst, or it can be a cancerous change which is actually a tumor called a melanoma.
Iris cysts are see through, originate from the ciliary body and are usually free floating. They sometimes get caught between the lens and cornea (clear outer past of the eye). We see them more in dogs, particularly Boston Terriers and Golden Retrievers, but they can be found in both dogs and cats.
Melanomas are not free floating and are usually not see through. They will eventually cause inflammation and pain as well as cataract formation, retinal detachment, and glaucoma so we recommend cats with a melanoma have the eye enucleated (removed). Even then however by the time we catch them they have often invaded into the tissue behind his eye, so an ultrasound of his eye to try to determine that would be very helpful.
Lymphoma is another tumor that we can see in a cat's eye, although it is generally found in the back of the eye, and we usually find it when we see a detached retina or bleeding in the eye.
If indeed this actually bleeding in his eye that usually points to some sort of inflammation in the eye (uveitis).
Inflammation can be from blunt or penetrating trauma, an infection including bacterial, viral (such as feline leukemia, feline immunodeficiency virus, Herpes, or feline infectious peritonitis), parasitic (toxoplasmosis), or fungal (cryptococcosis, or blastomycosis are two possibilities), glaucoma (increased eye pressure), or even cancer (melanoma, lymphoma, or sarcoma). Some cats with hypertension due to heart disease (primary or secondary to hyperthyroidism) or kidney disease can experience bleeding into their eye and/or a detached retina. Usually a detached retina looks like a floating veil seen in the pupil rather than what we are seeing with your fellow.
With what I can see from your picture I would be most concerned about bleeding (likely secondary to hypertension) or a melanoma.
It is difficult to tell which one your fellow has developed from the picture.
I highly recommend your kitty see a veterinary ophthalmologist to determine what is going on with his eye and what treatment should be pursued.
Here is a link to help you find one in your area:
His right eye does have a somewhat irregular iris border, but that is fairly common in older animals, and is a degenerative, non harmful change which does not affect function.
Please let me know if you have any further questions.