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Haigis-L Formula - Post Myopic LASIK

The Haigis-L Formula1

Using an IOLMaster corneal radius measured in mm (r meas), the Haigis-L 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 Haigis-L does is begin with a small intermediate area and then correct it based on a regression-derived 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, 2-variable, 3rd generation IOL power calculation formulas, such as SRK/T, Holladay 1 and Hoffer Q, which require an Aramberri double-K method correction to remove the artifact generated by a falsely flat central cornea.

For the IOL power calculation part, the Haigis-L and the Haigis formula are actually the same. The only difference between the two is that the myopic version of Haigis-L first calculates a new corneal radius based on the myopic Haigis-L algorithm.

The Haigis-L formula is now available on IOLMaster software version 4.xx and higher.

References:

1. Haigis W. Intraocular lens calculation after refractive surgery for myopia: Haigis-L formula. JCRS 2008; 34(10):1658-1663.

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