This file contains physical properties and IOL constants of popular IOL types. To add a specific IOL to your preferred list of available IOLs, you should insert the information of that IOL into the working list of IOLs included in the file ‘PhacoOptics.iol’ located in the program directory (default C:\PhacoOptics). Note: the PhacoOptics.iol file may by hidden in your Windows system. In that case you need to uncheck the ‘hidden’ property in the folder to make it visible and editable.