Fig. 39
Fig. 40
Figs. 38-40—Diagram showing position of streaks produced by Maddox rods as they appear to patients in making cycloduction tests.
To measure the duction range of the inferior oblique of the right eye, it is merely necessary to slowly rotate the Maddox rod before the right eye upward at its nasal end to the point where the band of light breaks so as to resemble a letter “X”. This gives in degrees the amount of right plus cycloduction, as indicated on the temporal scale, when it will appear to the patient, as shown in [Fig. 39].
The Maddox rod should then be restored to its original position, with the plus and minus on the 90 degree line of the scale ([Fig. 37]), and rotated upward at the temporal end until it again takes the form of the letter “X”. ([Fig. 40].) The position of the indicator will now denote the amount of right minus cycloduction, or duction range of the right superior oblique muscles. Having determined the duction range of the oblique muscles of the patient’s right eye, both Maddox rods should be placed in original position with rods horizontal and plus and minus sign on 90° of scale, as shown in [Fig. 37].
The Maddox rod before the left eye is then employed exactly in the same manner as before when the test for the right eye was made. A plus cycloduction of the left eye would be indicated, as shown in [Fig. 40], while a minus cycloduction of the left eye would appear to the patient, as shown in [Fig. 39].
By recording a comparison of each eye, as explained, it will be found that the range of duction usually averages five to twenty degrees on either side of the 90 degree line, as indicated on the scale surrounding the Maddox rods.