I thought it was only Dot's one eye that was affected too, Splashy. We haven't been shown her being told by a doctor that she shouldn't drive (at least as far as I can remember) but, if she was told, I suppose she thought it no longer applied since she believed her eyesight was improving.
What kind of idiot is Michelle for sleeping with the hateful Preston a few hours after he used poor Bex by charming her into bed to spite Michelle. It's pretty shocking behaviour on the latter's part (and that's before even considering he's her ex pupil!). I thought that at least she'd come to her senses now and realised she'd abused her position by having the affair - but apparently not! Are the writers trying to make her as unlikable as possible?