https://www.gov.uk/current-medical-g...-a-to-c#acuity
Group 2 entitlement vocational – lorries, buses
Drivers must have a visual acuity, using corrective lenses if necessary, of at least 6/7.5 (0.8 decimal) in the better eye and at least 6/60 (Snellen, decimal 0.1) in the other eye.