Eye and head contribution to gaze at near through multifocals: the usable field of view.

Presbyopes show that for targets presented within a 28 degrees clear field of view, gaze is accomplished by head and eye movements with head movements making an average contribution of 24%. A clear field of view which incorporates the factor of segment width provides an underestimation because of the factor of head movements. By including the effect of head movements, a fixed segment width provides a much wider clear field of view which we term the usable field of view.