All driving tests will start with an eyesight check. It’s a legal requirement that your eyesight is of the right standard. This means you must be able to read a number plate at 20 meters. If you can’t see something how can you deal with it.
Anyone who is a driver and certainly any professional driver should have their eyesight checked every 2 years. A professional eyesight check may reveal health problems. So for this reason it should be part of every drivers regular routines.
The distance of 20 meters is about 5 car lengths. This is the absolute minimum. A way used by a lot of driving instructors is to start at a distance well in excess of 20 meters then walk towards the number plate till you can read it.
If you take training with a professional instructor the first thing they should do is to check your eyesight. Not being able to read a number plate at this distance would mean you are not legal and therefore not safe either. Again if you cannot see it how can you deal with it.
If you are unfortunate enough to be involved in an accident. A police officer if he suspects there is an issue with your eyesight can and will check it. Traffic Officers do carry tape measures. If your eyesight is not legal you could find your licence revoked depending local police force deals with you. There will also be an insurance problem.
Bottom line is get your eyesight checked and check it regularly.