If one of the two yoke muscles lags behind the other or does not move the eye at all, images do not fall on corresponding retinal points, retinal correspondence is absent, the images become disparate, and diplopia results. These pairs of eye muscles yoke or move the eyes conjugately. Gaze up and to the right is accomplished by similar innervational activity to the right superior rectus and left inferior oblique muscles. Conjugate gaze to the right, for example, depends upon simultaneous and equal innervation to the right lateral rectus and left medial rectus muscles.

When a distant object is viewed with both eyes, the visual axes-a line connecting the center of the cornea with the fovea-are parallel or almost so, and each fovea receives an image of the object.īinocular single vision, defined as the coordinated use of both eyes to produce a single mental impression, occurs when each eye has intact foveal function and synergistic action of yoked extraocular muscles.

The law of projection of images establishes that an object forming its image on any point in the retina is projected to a point in space directly opposite.

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