HaigisL Formula  Post Myopic LASIK
The HaigisL Formula^{1}
Using an IOLMaster corneal radius measured in
mm (r
meas),
the HaigisL algorithm generates a corrected corneal radius (r corr),
which is then used by the regular Haigis formula to calculate the IOL
power. The corrected radius is calculated as follows:

331.5 
r corr = 
 

5.1625 x r meas + 82.2603  0.35 
So, if IOLMaster keratometry in mm following myopic LASIK is 8.82 mm x 090
and 8.63 mm x 180, the calculation of the corrected corneal radius would
be as follows:
Average corneal radius = (8.82 + 8.63)/2 = 8.73 mm = r meas

331.5 

r corr = 
 
= 9.0 mm 

5.1625 x 8.73 + 82.2603  0.35 

However, because here in North America we work in kertometric diopters, we need to convert the corrected corneal radius (r corr) in mm to a corrected central corneal power in diopters (D corr).
D corr = 337.5 / r corr
D corr = 337.5 / 9.0 = 37.50 D
This corrected, average corneal power in keratometric diopters is then used
with the regular Haigis formula to calculate the power of the intraocular
lens.
In essence, what myopic HaigisL does is begin with a small intermediate
area and then correct it based on a regressionderived algorithm. If this
corrected central corneal power is then entered into the regular Haigis formula,
it will do a good job with the calculation as the Haigis formula does not
tie the effective lens position estimation to the central corneal power.
This dependence on the central corneal power for the effective lens position
calculation is one of the drawbacks of older, 2variable, 3rd generation
IOL power calculation formulas, such as SRK/T, Holladay 1 and Hoffer Q, which
require an Aramberri doubleK method correction to remove the artifact generated
by a falsely flat central cornea.
For the IOL power calculation part, the HaigisL and the Haigis formula are actually the same. The only difference between the two is that the myopic version of HaigisL first calculates a new corneal radius based on the myopic HaigisL algorithm.
The HaigisL formula is now available on IOLMaster software version 4.xx
and higher.
References:
1. Haigis W. Intraocular lens calculation after refractive surgery for myopia:
HaigisL formula. JCRS 2008; 34(10):16581663.
