40
7.
Once calculated, results will automatically be imported into the IOL Calculator Screen
and used for IOL Power Calculations. Selecting the
[OK]
button without calculating will
close the calculator and save the values entered, but will not import a Kcorr to the IOL
Calculator.
8.
Use the
“
K Correction Method
”
drop
-
down box on the IOL Calculator Screen to see the
corrected corneal power (Kcorr) predicted by the other Post Refractive Formulas. If the
new method selected requires information that has not been entered, the Post Refractive
Calculator will open automatically. Once the desired Post Refractive Formula has been
selected, proceed with the IOL Power Calculation.
POST REFRACTIVE FORMULAS
It has been well established that the corneal power for patients that have undergone corneal
refractive eye surgery cannot be accurately measured using current keratometry or topography
methods. The Post Refractive Calculator included with the Scanmate software helps predict the
true corneal power for patients that have undergone corneal refractive surgery. The Scanmate
software is equipped to calculate the corrected corneal power (Kcorr) using History Derived,
Clinically Derived, Refraction Derived, Contact Lens Over
-
Correction and Double K methods.
These methods have been implemented as described by Shammas, H. John.
Intraocular lens
power calculations
. Slack Incorporated, 2004
HISTORY DERIVED
The History Derived method is considered to be one of the most accurate methods for
determining the true post
-
surgical corneal power. Unfortunately, it also requires the most
information about the patient –
some of which may not be available. This History Derived
method calculates the amount of correction that was achieved through refractive surgery and
adds it to the pre
-
surgical corneal power. This method can be used with 3rd generation formulas
(SRK/T, Hoffer Q or Holladay 1).
Required Inputs:
Pre Refractive Surgery K measurements
Pre Refractive Surgery Spectacle Refraction (S.E.)
Post Refractive Surgery Spectacle Refraction (S.E.)
CLINICALLY DERIVED
The advantage of this formula is that no information prior to the refractive surgery is needed.
The only input required for this method is the average (post
-
surgical) manual keratometry
measurement of corneal power. The disadvantage is that since the amount of correction
achieved through refractive surgery is unknown, it is not factored into the calculation. This
method can be used with 3rd generation formulas (SRK/T, Hoffer Q or Holladay 1).
Required Inputs:
Post Refractive Surgery K measurements
(
) (
)
−
−
−
−
=
pre
pre
post
post
ave
corr
S.E.
1
S.E.
S.E.
1
S.E.
K
-
pre
K
(
)
1
ave
corr
6.8m
K
-
post
x
1.14
K
−
−
=
