One thing you will see is a can of worms!

Firstly what criteria will tell the optometrist to be looking for?  A qualified optometrist can tell you what sort of glasses you might need and they have clear criteria for driving on the public highway. Are those criteria suitable for operating plant?

Then you need to get people to take the test. Are they contractually obliged to take the test?

Of course some might fail the test. Then will you be supplying them with suitable eyewear or other corrective measures?  You asked if you can   operate plant if you wear glasses? Well loads of organisations expect people to wear protective eyewear on site so why not protective eyewear with prescription lens? Anything else might be seen as discrimination.

Finally you will need to manage out those people who fail the test and who’s eyesight cannot be corrected.

You may need to step further back in your recruitment & selection processes.

Do you stipulate a minimum level of eye sight at recruitment? *bear in mind the Equality Act.

Does the policy state what happens if peoples eye sight deteriorates?

For persons hired to drive on the road there is a requirement their eye sight reaches the minimum standard and there is typically comment that loss of their road licence may end with employment termination.