The simulation video below shows the impact advanced glaucoma could have on the visual field of a driver. The patient wouldn't actually see black patches when looking ahead, but may be missing details/hazards if they are located in the damaged areas of the visual field.
The patient's view of this hazard is masked by their defect and they do not alter their gaze even at the late stage where the camera car 'brakes' to take evasive action. This patient has a binocular (both eyes) visual field that is on the borderline of satisfying the UK guideline for visual field fitness to drive.
This video was created by London's City University.
© 2010 Crabb et al.
Crabb DP, Smith ND, Rauscher FG, Chisholm CM, Barbur JL, et al. (2010) Exploring Eye Movements in Patients with Glaucoma When Viewing a Driving Scene. PLoS ONE 5(3): e9710. doi:10.1371/journal.pone.0009710