The area immediately in front of the nose/mouth is covered mainly by scent and touch as well as by the whiskers. Anything a bit further aways is actually covered by both eyes for a shorter distance.
Guinea pigs as prey animals have a wide angle sight ; it is sharp for about half a metre; afterwards they react to sudden movements. They have a small area ahead of their head that double/in-depth sight. However, eyesight is their weakest sense; they are much better at smelling, hearing and touch. They are perfectly adapted for the environment they have developed in; living mostly in dense undergrowth and moving along tracks between their denning area and their feeding gounds twice daily at dawn and dusk.
If you want to find out more about guinea pigs as a species, then you may find this link here interesting:
Guinea Pig Facts - An Overview