axis [ak´sis] (pl. ax´es)
1. a line through a center of a body, or about which a structure revolves.
the second cervical vertebra. adj., adj ax´ial.
the position of the cylindrical part of a lens
, used for correcting astigmatism
; the range of values is from 0° to 180°.
dorsoventral axis one passing from the posterior to the anterior surface of the body.
electrical axis of heart the preponderant direction of current flow through the heart, a consequence of the electromotive forces within the heart. It may be computed on either an instantaneous basis or a mean basis.
frontal axis an imaginary line running from right to left through the center of the eyeball.
axis of heart a line passing through the center of the base of the heart to the apex.
instantaneous electrical axis the electrical axis of the heart determined at a given point in time.
lead axis the imaginary direct line between the two electrodes of the bipolar leads or between the positive electrode and the reference point of the unipolar leads.
mean electrical axis the average direction of the activation or repolarization process during the cardiac cycle; it may be determined for any deflection (P, QRS, ST-T) and in the frontal, transverse, or sagittal plane.
1. a line connecting the center of the anterior curvature of the cornea (anterior pole) with that of the posterior curvature of the sclera (posterior pole).
2. the hypothetical straight line passing through the centers of curvature of the front and back surfaces of a simple lens.
a point located by drawing an imaginary line from the fourth intercostal space at the sternum and finding its intersection with an imaginary line drawn down the center of the chest below the axillae.
sagittal axis an imaginary line extending through the anterior and posterior poles of the eye.
an imaginary line passing from the midpoint of the visual field to the fovea centralis.
Axes of the eye. From Dorland's , 2000.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.