Refraction and muscular imbalance, as simplified through the use of the ski-optometer

by Daniel Woolf

Movement of Each Eye Singly

The movements of each eye individually are effected as follows:

The external rectus moves the eye directly outward; the internal rectus, directly inward.

The primary action of the superior rectus is to raise the eye. Because of the way in which the muscles run, obliquely from within outward, its lifting action increases when the eye is abducted and diminishes to little or nothing when the eye is adducted.

The inferior rectus carries the eye down. Owing to the oblique direction of the muscle, its depressing action increases as the eye is abducted and decreases to zero as the eye is adducted.

The inferior oblique is inserted back of the equator of the eye. Hence it pulls the back part of the eye down and consequently throws the front part up. It is thus an elevator of the eye, reinforcing the action of the superior rectus. Owing to the way in which it runs, from the front backward and outward, its elevating action is greatest when the eye is adducted, and diminishes to little or nothing when the eye is abducted.

The superior oblique, so far as its action on the eyeball is concerned, may be regarded as arising from the trochlea. From this point it runs backward and outward and is inserted back of the equator of the eye. It there pulls up the back part of the eye and consequently throws the front part down. It is thus a depressor, reinforcing the action of the inferior rectus. Owing to the oblique way in which it runs, its depressing action is greatest when the eye is adducted, and diminishes to little or nothing when the eye is abducted.