How does the ESCRS multi-formula calculator work?

We use a technology called web scraping. With the authorization of the formula authors, we are able to input the biometric data from our form into multiple websites at the same time, returning the same result you would get from doing the calculation in the original website.

What about the IOL constants?

The ESCRS IOL calculator suggests lens constants for a wide range of IOL models. If a formula suggests a specific constant for an IOL, this value is taken from the formula site. Otherwise, the suggested constants from the IOLCon website are used (optimized if available, if not those suggested by the manufacturer/ULIB). In any case there is a (i) information button to the right of the constant that shows where the constant was derived from and what other options are available. Furthermore, all values can be edited manually by the user.

What is IOLCon? What is ULIB?

IOLCon is an encyclopedic open online database for IOL design specifications and constants, developed by Prof. Achim Langenbucher in 2017. It is updated periodically with new IOLs and optimized constants. The ESCRS IOL Calculator uses IOLCon as a reference for its IOL database, sourcing the optimized and/or manufacturer/ULIB constants for use when a suggested constant for a specific IOL is none is available by the formula’s author.

ULIB is the “original'' constant database, developed by the late Prof. Wolfgang Haigis, which contains a biometer-specific optimized constant for a multitude of IOLs contributed by surgeons from all over the world. You may access these databases by visiting the websites: IOL Con at and ULIB at

Why are not all results shown for all IOL power calculation formulae?

Each formula has different accepted ranges for biometric parameters and IOL designs, so it is possible that the eye you are calculating is out of bounds for a specific formula. If you feel this may be an error, please send us a bug report using the contact information below.

Can I use this calculator for patients that previously had corneal refractive surgery (e.g. excimer laser or radial keratotomy)?

Currently the calculator should only be used in eyes that did NOT have previous corneal refractive surgery. This feature is under development.

What about toric IOLs?

Activate the 'Toric' switch and enter the additional parmaeters needed.

I think I’ve found a bug or an error! What should I do?

Please report it to us by e-mail to with as much detail as possible (and ideally with a screenshot). Feel free to also contribute with feature suggestions you may have for future versions of our ESCRS IOL Calculator.

An error has occurred. This application may no longer respond until reloaded. Reload 🗙