I think this could be entirely possible.
First things first, there is a somewhat similar technique already widely available in the animal world; the nictitating membrane.
This is basically a third eyelid that is transparent and protects the eye while still allowing vision. What you want is pretty much a supercharged version of this, so it shouldn't be too unlikely.
The biggest issue is having a strong enough bone like substance that would still be transparent (unfortunately I doubt it's possible to make a one way mirror organically) but nature to the rescue again!
This is a ghost shrimp. Now shrimp aren't exactly tough, but their shells are made of a chitin like substance, so it should be entirely possible to have a tougher but still transparent version like the ghost shrimp.
There are also insects with transparent shells like the tortoise shell beetle. So a chitin face plate is what your creature will want.
The final piece of the puzzle is why. What could cause such an adaption to evolve and become commonplace?
Fortunately that has an answer too. Many animals (snakes and skunks come to mind) have defence mechanisms that involve spraying their attacker with a particularly corrosive or noxious substance. This is most often aimed at the eyes as this will cause the most damage and allow the animal to escape.
Now imagine your proto creature lived in an area rich in such creatures. Those who could withstand the attack long enough to kill their prey would thrive and so the armoured eye plating would become commonplace and stronger.