164 Shifting and Swinging
vious point of fixation is seen worse. Even diplopia and polyopia1 do not prevent swinging with some im provement of vision. Usually the eye with imperfect vision is able to shift from one side of the card to the other, or from a point above the card to a point below it, and observe that in the first case the card appears to move from side to side, while in the second it appears to move up and down.
When patients are suffering from high degrees of eccentric fixation, it may be necessary, in order to help them to see worse when they shift, to use some of the methods described in the chapter on "Central Fixa tion." Usually, however, patients who cannot see worse when they shift at the distance can do it readily at the near-point, as the sight is best at that point, not only in myopia, but often in hypermetropia as well. When the swing can be produced at the near point, the distance can be gradually increased until the same thing can be done at twenty feet.
After resting the eyes by closing or palming, shifting and swinging are often more successful. By this method of alternately resting the eyes and then shifting, persons with very imperfect sight have sometimes obtained a temporary or permanent cure in a few weeks.
Shifting may be done slowly or rapidly, according to the state of the vision. At the beginning the patient will be likely to strain if he shifts too rapidly; and then the point shifted from will not be seen worse, and there will be no swing. As improvement is made, the speed can be increased. It is usually impossible, however, to realize the swing if the shifting is more rapid than two or three times a second.
1 Double and multiple vision.