Rather than simply move a fixed formula-specific IOL power prediction curve
up (more IOL power recommended) or down (less IOL power recommended), the
Haigis formula instead uses three constants. Haigis Formula Optimization Spreadsheet
Here is a Microsoft Excel spreadsheet that can
be used to calculate an average IOL constant based on data from 100 patients
for the four popular IOL power formulas (Holladay 1, Hoffer Q, SRK II
and SRK/T). Constants ~ 4-IOL Calculation
Formulas
Optical coherence biometry using the Zeiss IOLMaster is a state of the art technique for measuring axial length. By partial coherence interferometry, the IOL Master achieves a level of accuracy and reproducibility never before seen. Here is the IOLMaster online user's manual.
Measuring axial length with the IOL Master allows a high degree of flexibility. Rather than simply positioning a small, in-focus image in the middle of a set of video screen cross hairs, you can instead maneuver the focusing spot anywhere within the measurement reticule. Best Techniques for Axial Length
Very often, the described problems can be traced down to keratometer indices and/or to peculiarities of corneal power implementations in the IOL formulas of the respective instruments.
Keratometer Measurement
If you have not done so already, now is the time to incorporate one
of the newer theoretic IOL formulas. Follow this link for comparisons
of the various IOL power formulas in current use:
IOL Power Formulas
A-Scan Biometry using ultrasound, an important and sometimes challenging
preoperative measurement, can be carried out in several ways. In this section,
we will compare the advantages of the immersion technique over applanation,
and how to improve accuracy. A-Scan Biometry Using Ultrasound
Prior keratorefractive surgery will make direct measurements for corneal
power problematic. Learn how to to estimate the true corneal power following
RK, PRK, and LASIK.
IOL Power after LASIK, PRK, RK
