Over the last decade, IOL power calculations have become a focal point of cataract surgery. In 1977, the state-of-the-art method for estimating IOL power for emmetropia was to add +18.0 D to 1.25 times the pre-cataractous refraction. A decade later, being within ±1.00 D of the target refraction was still considered a reasonable standard. The standard for accuracy for normal eyes has since considerably increased and is now above 80% for a ±0.50 D accuracy.
Today, by carefully optimizing the individual components of IOL power calculations and applying validation criteria in conjunction with advanced surgical techniques, it is possible to achieve accuracy within ±0.50 D for 90% of surgeries and ±1.00 D for better than 98% of surgeries. By tracking your outcomes, you can see where you stand in relation to this published “benchmark” standard.
Dr. Hill volunteers a significant amount of his time and resources to make the information on the physician side of this website available. Physicians have expressed their desire to donate. If you would like to express your gratitude, your contribution is welcome and graciously appreciated.
Hill-RBF Calculator
The Hill-RBF Calculator is an advanced, self-validating method for IOL power selection employing pattern recognition and sophisticated data interpolation. It has been optimized for the Haag-Streit Lenstar, using optical biometry for all axial measurements and high-density autokeratometry.
Referral IOL Power Calculation Guidelines
It is always recommended that, before referring a patient to our practice for IOL power selection, the referring surgeon (not support staff) contact Dr. Hill first to discuss the case and surgical objectives.
Haigis Formula Optimization
Rather than 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. Below is a link to the page where physicians may download the forms to fill out and request Haigis formula optimization. This service requires physician-to-physician communication and will not be initiated at the request of support staff.
- Haigis Formula Optimization (download forms)
Optical Biometry Lens Constants
Because there is no corneal contact, optical biometry lens constants will always be higher than those optimized for applanation A-scans, in which a variable amount of corneal compression occurs.
A-Scan Ultrasound Biometry
Pre-operative A-scan ultrasound biometry for pre-operative measurement can be carried out in several ways. In this section, we will compare the advantages of the immersion technique over applanation biometry and how to improve accuracy. A-scan biometry using the immersion technique exhibits better reproducibility, resulting in an overall increase in accuracy. However, compared to optical biometry, all forms of ultrasound-based biometry may have accuracy limitations. Follow the links below for advanced A-scan ultrasound biometry techniques to improve your axial length measurements using this technology:
Prior Keratorefractive Surgery
Prior keratorefractive surgery will make direct measurements of corneal power problematic. Follow these links to learn how to estimate the true corneal power following RK, PRK, and LASIK.
Post Myopic LASIK
The following links provide descriptions of several popular IOL power calculation methods in relation to the various ablative forms of keratorefractive surgery for myopia, including LASIK and PRK.
Effective Lens Position (ELPo)
Determining the Effective Lens Position (ELPo) for each IOL and each surgeon is an effective way to minimize the prediction error. 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.
