Calculations of Intraocular Lens Power

To the Editor.  —In the April 1986 issue of the Archives, Holladay and coworkers¹ present a lucid description of factors affecting the calculation of intraocular lens power and make reasoned recommendations on how results may be improved. Their empirical data, however, require comment.Reexamining the 26 subjects with "surprise refractions" (postoperative deviations from "target" values by more than 2 diopters [D]), they found that "errors" in their preoperative readings accounted for almost one half to two thirds of the observed deviations. This may indeed be true. Alternatively, their results may simply reflect "regression to the mean." In its simplest form, this states that when dealing with unusual events (tail ends of a spectrum or outliers), almost anything you do will yield more "normal" results, quite independent of other factors. One way of assessing the degree to which this influenced the observations would be to reexamine all 512 original subjects,