Good peripheral vision is vital on track. With your primary focus on the next reference point (apex/exit for example) your peripheral vision is used to position you on the track. Also your peripheral vision is vital for keeping track of cars around you while you focus on driving.
A good way to train your vision is to use a Batak wall. This piece of equipment uses randomly flashing lights which you must extinguish by tapping them. The spread of the lights helps develop your peripheral vision.