Confirmation and refinement of the Diehl-Miller nomogram for intraocular lens power calculation after laser in situ keratomileusis.

PURPOSE

To validate the Diehl-Miller equation for achieving emmetropia after cataract surgery in post-laser in situ keratomileusis (LASIK) eyes and to present a refined equation.

SETTING

Jules Stein Eye Institute, Los Angeles, California, USA.

DESIGN

Cohort study.

METHODS

Preoperative and postoperative refractive and cataract surgery data were collected from the medical records of post-LASIK patients. The IOL power data and postoperative refractive information were used to calculate the true target refractive error that should have been chosen to achieve emmetropia. Regression analysis of the combined data from Diehl-Miller and the current study was used to develop a refined equation. Diehl-Miller relates the manifest refraction spherical equivalent (MRSE) change induced by LASIK to an adjusted target postoperative refractive error to be used in intraocular lens (IOL) power calculations.

RESULTS

Twenty-three eyes of 18 patients were evaluated. The target refractive error calculated by Diehl-Miller differed from the true target refractive error by an absolute mean of 0.481 diopter (D) ±0.376 (SD). Regression analysis of the combined data from Diehl-Miller and the current study yielded the following 2nd-order polynomial equation: Target refractive error = -0.0198 (MRSE change)(2) +0.170 (MRSE change)-0.0079. The calculated target refractive error fell within ±0.50 D of the true target in 49% of patients and within ±1.00 D in 93% of patients.

CONCLUSIONS

This study validated that the Diehl-Miller equation accurately predicts the target refractive error to achieve emmetropia in post-LASIK eyes. The slightly refined Diehl-Date-Miller equation and associated lookup tables can be used to avoid postoperative refractive surprises.