IOL Power Calculations
How to Achieve Accurate Results

Intraocular Lens Power Calculations.

IOL power calculations have become the main focal point of refractive surgery in a relatively short period of time. As recently as 1977, the state-of-the-art IOL power calculation to achieve emmetropia with a posterior chamber IOL, was simply adding +19.0 D to the pre-cataractous refraction. Around 1990, with the formulas available at that time, being within ±1.00 D of the target refraction was considered perfect.

Today, by paying attention to IOL power calculations and advanced surgical techniques, it is possible to be within ±0.50 D in 95 percent of surgeries or better, and fast becoming the standard.

Surgically-induced Astigmatism Calculator

Now, there is no need to delve into mathematics. The SIA Calculator removes the task of drawing vectors or looking up sines, cosines and their relatives. Just push a few keystrokes and the job is accurately and speedily done.
Surgically-induced Astigmatism Calculator (SIA Calculator)

Haigis Formula Optimization

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

4-IOL Constants

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

IOLMaster

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.

Best Techniques for Axial Length

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

Keratometer Measurement

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

IOL Power Formulas

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

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

IOL Power after LASIK, PRK, RK

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

A-Scan Ultrasound Biometry

A-scan biometry by immersion has better reproducibility, which leads to an overall increase in accuracy. However, all forms of ultrasound based biometry have limitations. Follow the links below for advanced A-Scan biometry techniques to improve your axial length measurements.

A-scan Biometry
Biometry Explained
A-scan Setting

Applanation A-scan
Immersion A-scan
Immersion Vector A/B-scan

Prior Keratorefractive Surgery

Prior keratorefractive surgery will make direct measurements for corneal power problematic. Follow these links to learn how to to estimate the true corneal power following RK, PRK, and LASIK.

Myopic LASIK
Hyperopic LASIK
Radial Keratotomy

Double K Formula Corrections

Hoffer Q Formula

Holladay 1 Formula

SRK/T Formula

ASCRS Post Keratorefractive Calculator

Effective Lens Position (ELPo)
(Anterior Chamber Depth)

Determining the Effective Lens Position (ELPo) for each IOL and each surgeon is an effective way to reduce the prediction error to a minimum. The ELPo allows you to calculate the optimal or "personalized" lens position based on your individual experience with any style lens averaged ideally from at least 20 to 30 cases.

Effective Lens Position (ELPo)
ELP Spreadsheet

Post Myopic LASIK

The following links contain descriptions of several popular IOL power calculation methods as they relate to the various ablative forms of keratorefractive surgery for myopia, such as LASIK and PRK.

Clinical History Method
Contact Lens Method
Corneal Bypass Method
Feiz-Mannis Method
Latkany Method

Masket Method
Modified Maloney Method
Modified Masket Method
Oculus Pentacam
Topographic Central Power