The Next / Previous Horizon option allows you to move through the horizon list without having to open the Horizon tab in the Layer Manager bar.
Toggle the Previous or Next buttons to cycle through events in the database.
OR
From within the Seismic window, press <H> on your keyboard to display the previous event, or press <h> on your keyboard to display the next event. The Next / Previous option posts each horizon in turn, skipping any faults in your horizon/fault list.