I doubt it's a "heart problem showing up in your eyeball". Rather, it's likely that the eyeball is just a convenient place to non-invasively look at the structure of small blood vessels. And various cardiovascular conditions show up in small blood vessels all over your body. It likely has nothing to do with your eyeballs specifically. I.e. if a portion of your upper arm were translucent, this same methodology could likely be applied there as well. It's just that a translucent upper arm is not part of most human's biology.

There are already well established methods of examining the back of your eyeball for other evidence of other conditions.