Axial and instantaneous power conversion in corneal topography
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1School of Optometry, University of California, Berkeley 94720-2020, USA.
Purpose:
To determine if a direct relationship exists between the two common measures of corneal topography--axial and instantaneous powers--that are based on corneal slope or curvature, respectively.
Method:
The theoretical relationship between axial and instantaneous powers was derived for unrestricted shapes using equations of basic calculus.
Results:
It was found that axial power at any point y on the cornea is exactly equal to the average of the instantaneous powers from the axis to point y.
Conclusions:
A simple relationship exists between axial and instantaneous powers that is valid for the intersection of any surface by a meridional plane. This provides a practical means for converting between axial and instantaneous powers for clinical applications of corneal topography.