At every railway medical I have attended, you are given this colour blind test, and thats a lot of medicals.
As a guard, when shunting a train 75SLU's long your eyesight and colour preception have to be near perfect to sight distant signals.
The drivers eyesight test is to make the bottom line of the test, and the guard next to the bottom line.
BR provided railway issue spectacles, which were to a set standard.
These were issued to drivers and guards to a recent eye test prescription.
For the eye sight test glasses could be worn.
( I have a drawer full of old railway glasses.)
Also if your were traincrew, you had to have a spare pair of glasses when on duty.