Interpreting the Defocus Equivalent Index

To the Editor: In his recent article, Waring1 makes a number of excellent proposals for standardized graphs of refractive surgery outcomes. This is a very important issue. Adopting graphing standards provides researchers with a framework for planning data collection and for its final presentation. It also allows readers to make easy comparisons between different reports. Dr Waring should be commended for his efforts. However, it may be relevant to make some comments about the proposed defocus equivalent (DE) index, a function of the magnitude of sphere (S) and cylinder (C) (Waring’s Figure 3). Dr Waring has graciously informed me that his definition for defocus equivalent (essentially DE = S + 1/2 C ), was published erroneously and should be as originally suggested by Holladay and colleagues2 for the relaxed unaccommodating eye, ie, the absolute magnitude of spherical equivalent plus the absolute magnitude of half the cylinder (see Errata on page 294 of this issue):