I'm sure there are lots of reasons for not being aware of things a couple of squabbling kids in the back wouldn't help that being said if you can't see it you certainly can't be aware of it. A lot of people think glaucoma is high pressure but a lot of the definitions don't include pressure. A third of people who develop it have a normal pressure on diagnosis some progressively lose sight with a normal pressure. Its really optic nerve dammage thats why you can't regain any sight lost . The higher the pressure the more likely sight loss is but like anything to do with health some are just unlucky.Both OH and I have glaucoma. Fortunately my pressures are stable but OH had a Trabeculectomy in the early autumn. In her case we are still waiting to have a DVLA sight test for her licence renewal which was sent off in May. Specsavers have always done field vision tests on my periodic visits even before I was diagnosed with glaucoma.
Often it's not vision issues when driving, it's people's awareness. I don't know if it is an increase in motorway driving that makes them switch off instead of concentrating.