COMPUTERIZED VIDEOKERATOSCOPES DATA DISPLAY

Curvature Maps

The values used to draw the curvature maps 
can be calculated based on the axial or the 
instantaneous corneal radius.

The axial radius (also called the sagittal 
radius) is the distance normal to a 
peripheral corneal point to a single axis.  

The instantaneous radius (also called 
tangential, true or local radius) is a radius 
of a peripheral point which is independent 
of any axis of the cornea.  With the cornea, 
as it becomes more aspheric in the 
periphery, the center of curvature moves 
away from the central axis of the cornea 
forming a locus of centers of curvatures.  
The instantaneous radius is more accurate and sensitive to 
changes in curvature.  It is longer than the axial radius.