It is important to take into account that changing optotype size is not the same that correcting vergence by proximal distance. This is a concept that generates confusion as we have seen in many of the courses we have conducted about Defocus Curves. 

In this article we will explain the lens preparation procedure to be carried out before starting to measure a Defocus Curve, in general with any test, and in particular with the Multifocal Lens Analyzer PRO (MLA).

Failure to understand the purpose of why certain visual performance measures are taken can lead to the development of clinical trial protocols with long duration and therefore unreliable data due to patient fatigue.