OpenOptix ABO Study Guide - Laramy-K Optical

z= Ay 2 +By 4 +Cy 6 +Dy 8 +Ey 10
A=1/2r
B=p/8r 3
C=p 2 /16r 5
D=5p 3 /128r 7
E=7p 4 /256r 9
This expansion allows the shape to be manipulated to varying degrees as it gets further
from the axis without directly affecting the axis. This expansion can also be used to
define a more simple conic section by setting the B, C, D, and E variable to 0, therefore
only the a value remains and defines the conic.
Aphakic
Aphakic lenses use aspherics because plus power lenses higher than +8.00 are outside of
the Tersching ellipse and do not have a best form curve. This means that in order to
provide the best vision the lens designer has no choice but to use aspherics. Usually you
will find that the aphakic lens not only uses asphericity to optically improve the
performance of the lens, but often the lens uses again deformed conicoids to provide
cosmetic appeal to the lens as well since often times high plus powers will be thick.
Keep in mind that aspherics when referred to in ophthalmics can be placed on both the
front or back surface of the lens and as free form technology takes a hold in our industry
we will be seeing varying degrees of eccentricity on both the front and the back of all
lenses to improve cosmetics and optics.
This document is licensed under the Creative Commons Attribution 3.0 License. 7/30/2009
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