alpha angle

n.
  1. The angle between the visual and the optic axes as they cross at the nodal point of the eye.
  2. The angle between the visual line and the major axis of the corneal ellipse.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.