How do I obtain a piggyback IOL calculation following a primary IOL placement?
You simply use the Holladay Refractive (R) formula on the IOL CALC SCREEN. Put the CURRENT POST OP REFRACTION (+2.00) on the PREOP SCREEN and put in the TARGET REFRACTION (e.g. -0.50). When you chose the Holladay R it will display the SECONDARY PIGGY BACK IOL POWER (which is also the power that needs to be added or subtracted from the current IOL). So, if it shows +2.50 as in this example, you would put a +2.50 D Piggy Back in the SULCUS or ADD +2.50 D to the existing IOL Power for an EXCHANGE.
The built-in help system is also very helpful. Search for piggyback.