IOL Power Calculation Formulas.
For axial lengths from 22.50 mm to 24.00 mm, and central corneal powers ranging from 42.00 D to 45.00 D and a normal anterior chamber depth, most modern IOL power calculation formulas will give good outcomes. However, for eyes outside this range, our results indicate that Haigis (with properly optimized a0, a1 and a2 constants) and the newer generation formulas, such as Holladay 2, Olsen and Barrett give better results.
For Holladay 1, SRK/T, Haigis and Holladay 2, an adjustment is required for the high to extreme axial myope and axial lengths above 25.00 mm. How to do this is outlined at:
The Journal of Cataract and Refractive Surgery paper that describes this approach can be found at:
Wang L, et al. Optimizing intraocular lens power calculations in eyes with axial lengths above 25.0 mm. JCRS 2011; 37:2018-2027.
Here is something to consider. As surgeons, we are now mostly being judged by our patients and our peers by our refractive outcomes. It seems to a little odd to spend tens of thousand of dollars on the next most accurate measurement technology, but continue to rely on calculation methods that are not from this century. Optimal outcomes require the best possible measurement technology and the best possible calculation methods.
The chart below represents our experience with popular IOL power selection methods where the measurements have been made by optical biometry. We are now using only the Barrett Universal II formula and the Hill-RBF pattern recognition method for all of our calculations. For the high to extreme axial myope we will also look at the Wang-Koch axial length modification of the Holladay 1 formula. Eight years of experience has shown the best pre-operative measurements have been with the Haag-Streit Lenstar.