Direction of the Gaze
There are six cardinal directions of the gaze, each corresponding to the field of action of one of the six ocular muscles as follows:
| Cardinal Direction: | Muscles Specially Active: |
|---|---|
| Straight out | External rectus |
| Straight in | Internal rectus |
| Up and out | Superior rectus (as an elevator) |
| Up and in | Inferior oblique (as an elevator) |
| Down and out | Inferior rectus (as a depressor) |
| Down and in | Superior oblique (as a depressor) |
It is to be noted that the action of each muscle does not absolutely stop at the middle line, but extends somewhat beyond it. Thus the action of the right externus extends not only throughout the whole right half of the field of vision, but also some fifteen to twenty degrees to the left of the median line; and that of the superior rectus extends not only above the horizontal plane but also somewhat below.