@kratzer
I think this actually looks much better.

@kratzer  
heh, author wanted to be a professional artist and make a big show off, but failed

@Ponylooker You’re correct - it’s a bulge. But it’s not a rough step with strict borders (which would be perfectly visible) - it’s a very smooth bulge (on healthy eye), which deviate an <human> eyeball from sphere shape by ~4%. How often can you discern such “defects” on natural round stones? Mind that it’s an ridiculously sized cartoon character eyeball, where focal length should be even smaller. At least borders for cornea should be quite blurred, not that clear.  
As for screenshot from the show - it deliberately was done this way. Try to remove those features and picture will become outright creepy for children (don’t forget that it’s show’s target audience).

@Background Pony #020E  
The cornea is physically a bulge, so it’s possible it would be visible. When Twilight got stoned, iris and (incorrectly) pupil were visible, but (correctly) not shaded:
 

@kratzer It should be even more creepier - no iris, no pupil, just plain sclera. After all, eye is almost round ball from outside and those discernible details are inside of it, not outside. And until stone has translucent features - they wouldn’t be visible.

@Ponylooker  
It looks worse  

One thing artists consistently mess up with petrification is the eyes. They should be blank. They absolutely should not have reflections and highlights in them.

being turned into a stone fetish or likening?

Must end life in classic Lorne Green pose. Best petrification ever!

Useful against unwanted bat pony bites.