A comparison of the left eye shows adduction of 18 degrees with an abduction of 8 degrees, proving a lateral insufficiency because the ratio is less than 3 to 1; and the muscles of the left eye are at fault. The power of 2 degrees superduction and 2 degrees subduction, proves that no weakness exists in the vertical muscles. After making the duction test for each eye individually, a comparison of both eyes in relationship to each other may be more readily determined by following the dotted lines (Fig. 24). As previously stated, it is the inability of the two eyes to work together that causes the imbalance, so that if both eyes were normal, the adduction, abduction, superduction and subduction of the two eyes would agree. The duction chart (Fig. 24.) also shows that the corresponding muscles of each eye agree—with the exception of the adduction of the right eye and the left eye. This proves that the left internus is weak, measuring only 18 degrees instead of 24 degrees; it further proves the 6 degrees of exophoria in the monocular test, as was quickly and more readily determined in the binocular test. Likewise, in cases of esophoria, hyperphoria, or cataphoria, the making of definite muscle measurements independently through the prescribed method would show through the merest glance at a similar diagram which muscle or muscles were relatively out of balance. Heterphoria of almost any type, or tendencies other than normal, may be fully investigated by making a thorough and separate test of each muscle. Where an imbalance exists, a rapid test may be employed to distinguish a pseudo or false condition from a true condition. This is accomplished by first placing the two Maddox rods (both the red and white) so that the rods lie in a vertical position. If the two lines fuse, we have determined the existence of a false condition caused by a possible error of refraction or nerve strain. If the lines separate, we have determined a true muscular condition, and then only should the second method of muscular treatment follow. [Illustration: _Same as Model 215 but Automatic Cylinder Arrangement omitted._ SKI-OPTOMETER MODEL 205 Embodying Spherical Lenses Combined with Appliances for Testing and Correcting Muscular Imbalance.] CHAPTER IX FIRST METHOD OF TREATMENT OPTICAL CORRECTION The mere determination of the degree of an imbalance, or even the diagnosis of a patient’s trouble, is not sufficient. If relief is to be secured, something more must be accomplished. As previously stated, muscular imbalance may be corrected through one of the four following rules or methods, each explained in their relative order: 1—Optical Correction 2—Muscular Exercise 3—Use of Prism Lenses 4—Operative Methods ESOPHORIA