Pupil size and Scheimpflug Holladay equivalent keratometry readings

media (air and aqueous) that bound the cornea. The 1.336 value used in our formula is the refractive index of the aqueous and vitreous at body temperature. The original Hoffer formula was restated in the Hoffer Q paper referenced in our article. The original reference is shown below. Holladay recommended that we repeat our study by back-calculating the K values again using modern formulas (Hoffer Q, Holladay 1 and 2, SRK/T). While this exercise is interesting in theory, the results would be erroneous because each of these formulas calculates ELP based on biometric data and an A-constant or surgeon factor. It is not possible to rearrange the formulas to input a measured IOL position. We plan to work with Holladay and Oculus to refine the methods used to study the Pentacam and other Scheimpflug cameras, with the goal of improving the accuracy of these devices in post-keratorefractive surgery eyes. We applaud Oculus for producing the device and Holladay for his software contributions. We think the Pentacam is a remarkable piece of technology, but we also consider it a work in progress.dQiongyan Tang, MD, Kenneth J. Hoffer, MD, Michael D. Olson, OD, PhD, Kevin M. Miller, MD