If there is no spot on the string were normal fixation can be achieved, the use of loose prisms may be necessary. This is done by finding the point on the string where the least amount of prism is needed to achieve fusion, and expanding the range from that point. Once the range is expanded to include the entire string, the prism is reduced and the process begun again. Once normal fusion and fixation can be achieved at all distances, the next goal is to be able to jump quickly from one bead to another achieving proper fixation each time. The position and separations of the beads should be varied during this part of the training to include many different possibilities. Once this has been successfully accomplished, next goal is to be able to look away from the beads at a distance object and then look back at them and regain fusion, alternate beads after each distance glance. The Brock string may also be used in connection with prism flipper bars, accommodative flippers, balance boards, and other devices to make the task more challenging. The object of any Brock string training is to be able to have the subject see the strings cross exactly at the bead he or she is looking at. Everything in front of and behind this bead should be doubled. If not, have the subject find some spot on the string where it is possible to achieve the proper image (strings crossing exactly at the bead). From this point he or she will slowly slide the bead closer then further from them, maintaining proper alignment and fusion. The goal is to expand the range from this point until normal fixation can be obtained at all distances.