Please tell me the meaning of these lines in simple English it's complicated for me to understand it's about medical related guidelines

You need to have good enough vision for whatever the duty you would be performing is. It's okay if your vision is only good enough when using glasses, as long as you would be wearing them for the duty. The numbers are technical language for measuring vision, and *I think* they mean that, for one of the occupations, if a person with normal eyesight would be able to see the thing clearly from 6 feet away, you would need to be able to see it clearly from a minimum of 6 feet away, and for another of the occupations if a person with normal eyesight would be able to see the thing clearly from 9 feet away, you would need to be able to see it clearly from a minimum of 6 feet away.

Your eyesight needs to be good enough for the job. For some jobs, your eyesight must be 6/6. That means normal vision. Average. For other jobs, your eyesight must be 6/9 (or better). 6/9 is below average. It means that you can see things from 6 meters away, which an average person can see from 9 meters away. You can wear glasses for the test.

OP, a further example; I have to wear glasses for driving. In the UK, when you do a driving test, you have to read a number-plate from 20 metres away. That is, the registration number. You can read it *with or without glasses.* If you cannot read it, they stop the test and you fail to get your licence. I cannot read a number-plate from 20 m without my glasses. I can with them on. I wore my glasses when I went for the test. There is a marker on my driving licence, which says I must wear glasses when driving. If the police stop me, and I'm not wearing my glasses, I will be in trouble. --- I hope that helps to explain. "With or without glasses" means that you *can* wear them if you *need* to.

You have to have eyesight (vision) that’s good enough for you to do the job. Generally speaking, you need an equivalent of 1.0 (in American English we’d say 20/20, read “twenty-twenty”) with glasses, and 0.67 (20/30) without glasses.

You need good eyesight. If you wear glasses, they can't be too bad.