S
S
E
E
R
R
V
V
I
I
C
C
E
E
M
M
A
A
N
N
U
U
A
A
L
L
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ESIRIS -
- Version 1.0 Date: 22.09.00
Appendix
The following appendixes include details of the laser and precise descriptions, which
provides the user a better understanding. They are not necessary for ordinary use
and so they are not part of user manual.
Appendix A: Calculation Basis
A1. Introduction
For correction of myopia and hyperopia on human eyes, it is necessary to flatten the
bounding of the corneal surface or to rise it. If furthermore an astigmatism should be
corrected, the bounding of the cornea has to be changed differently in two meridians.
Picture 17: Schematic drawing of corneal correction in
section.
Correction of Myopia
R1 < R2
Correction of Hyperopia
R1 > R2
The areas, treated with excimer laser are darkened.
d = diameter of optical zone,
h = maximum depth of corneal incision
b = width of transition zone at hyperopic correction
R1= bending radii of cornea before treatment
R2= bending radii of cornea after treatment
Based on the change of bending on corneal surface, the power of refraction is
changed referring to the following formulae:
D = (1-n) x ( 1/R2 – 1/R1)
h
d
d
b
h
R 2
R1
R1
R 2
