Why cannot I order PC lenses?

This is my third time to buy new prescription eyeglasses in the past half year, I need to work under tough circumstance every day, I am a welder actually, and I have been bored of selecting mountains of frames every time, I want to buy PC lenses, as they are more durable and anti-scratched than ordinary lenses, but as I had a really strong prescription, my optician told me that it was not suitable for me to order such lenses, I just want to know the Rx restriction of ordering such lenses!