Making high quality eyes

Often, the eyes of characters that aim for photorealism fall far short and stand out in a bad way. I’d like to discuss what would be required to approach real time photorealism as much as possible when making eyes. I know that real time 100% photorealistic eyes are currently impossible and I’m not that much into photorealism but I think knowing about it can be useful.

Here’s the anatomy of the human eye:

So, we’d need subsurface scaterring, translucency, refraction and clear coat right? Am I missing anything?

Are there required elements which can be combined without much loss of quality?

The lighting model should be subsurface.
The blend mode should be translucent, two sided.
The translucent mode should be volumetric directional or surface, I’m not sure which.
It should have a refraction depth bias.

The shading model should be Subsurface Profile since it has the highest available SSS shading model. It also has few possible inputs. Can it take translucency and refraction?
Would another one of the SSS profiles add enough inputs?

Perhaps the shading model should be clear coat since the eye has a cornea on the outside.

Would we need two objects, one inside the other?