IOL Power Calculation Formulas.
For axial lengths from 22.50 mm to 26.00 mm, and central corneal
powers ranging from 41.00 D to 46.00 D, almost any modern IOL power
calculation formula will give good outcomes. However, for eyes
outside this range, our results indicate that newer generation
formulas, such as Holladay 2, or Haigis (with properly optimized a0,
a1 and a2 constants) are better choices.
As presented by Dr. Wolfgang Haigis, at the 2001 San Diego ASCRS
meeting, the individual geometry of each intraocular lens also plays
a role in determining which formula works best. For example, with the
Alcon MA-series 3-piece intraocular lenses, we have found that the
Holladay 1, Holladay 2 and Haigis formulas give the optimum results.
For other types of intraocular lenses, SRK/T, or Hoffer Q, may offer
better outcomes, depending on the axial length and the individual geometry
of the particular lens used. This small advantage of one formula over
another is the result of the power prediction curve of, say the Hoffer
Q formula being a better match for the AMO SN40 3- piece lens at higher
IOL powers than the Holladay 1 formula.
In the partially optimized form (IOLMaster software), with the a0
constant optimized and the a1 and a2 constants set at default values
of 0.4 and 0.1 respectively, the Haigis formula performs well for eyes
of normal to slightly long axial lengths and relatively short axial
lengths. But when the a0, a1 and a2 Haigis constants have been fully
by regression analysis, the Haigis formula performs well across a very
wide range of axial lengths. Please visit our Physician Downloads for instructions and an Excel spreadsheet that will
allow you to carry out this three variable Haigis
Worth repeating, our recommendation is that you carefully track your
outcomes, using several formulas for each IOL. The accuracy of these
formulas is noticeably increased when the A-constant, ACD, or Surgeon
Factor are "personalized." For this reason, maintaining, and
systematically reviewing, an Outcomes
Database should be an essential
part of your practice, and well worth the extra effort.
Utilizing a fully optimized version of the Haigis formula, or the
Holladay 2 formula, in conjunction with the Zeiss
mean absolute post-operative prediction error runs slightly better
D. Given the fact that IOLs presently come in 0.50 D
steps, these results approach the theoretic limit of the exercise.