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The Sense of Sight / All About the Eyes
Page: 12
It is worthwhile at this point to define certain axes of the eyes employed during different types of study. The optic axis of the eye is a line drawn through the centre of the cornea and the nodal (central) point of the eye; it actually does not intersect with the retina at the centre of the fovea as might be expected, but toward the nose from this, so that there is an angle of about five degrees between (1) the visual axis—the line joining the point fixated (the point toward which the gaze is directed) and the nodal point—and (2) the optic axis.
The general modes of action of the six extraocular muscles have been described in connection with their anatomy: rotation of the eye toward the nose is carried out by the medial rectus; outward movement is by the lateral rectus. Upward movements are carried out by the combined actions of the superior rectus and the inferior oblique muscles, and downward movements by the inferior rectus and the superior oblique. Intermediate directions of gaze are achieved by combined actions of several muscles. When the two eyes act together, as they normally do, and change their direction of gaze to the left, for example, the left eye rotates away from the nose by means of its lateral rectus, while the right eye turns toward the nose by means of its medial rectus. These muscles may be considered as a linked pair; that is, when they are activated by the central nervous system this occurs conjointly and virtually automatically. This linking of the muscles of the two eyes is an important physiological feature and has still more important pathological interest in the analysis of squint, when the two eyes fail to be directed at the same point. Take this preliminary to see if your condition could respond to treatment.
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Additional information regarding conditions of the eyes can be found here.
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