There is no legal guidance that employers should pay for prescription safety goggles. However, if you need to wear safety goggles for you job, you can wear non-prescription goggles over your prescription glasses and your employer should provide you with non-prescription goggles of good quality for free. If you want to get prescription safety goggles, you can talk to your employer abiut it and I guess he will be willing to buy prescription safety goggles for you due to the requirement of the job.
I think you should talk about it to your employer. Some employers will give their glasses staff an allowance towards their glasses. But not all employer will offer that allowance. And as far as know, there is no Employment Law guidelines that they ought to provide prescription safety goggles. So, you may have to pay for it yourself. Good luck.