Intraocular lens power calculation using standard formulas and ray tracing after DMEK in patients with Fuchs endothelial dystrophy

BACKGROUND: The study presented here aims to optimize the accuracy of intraocular lens (IOL) power calculations in patients after DMEK by evaluation of the impact of the altered anterior/posterior corneal curvature relationship. METHODS: Scheimpflug-based Oculus Pentacam imaging was performed after DMEK surgery for Fuchs endothelial dystrophy. The IOL power was calculated for all patients by ray tracing, aiming for postoperative emmetropia. We also performed the IOL calculation using four third-generation formulas (SRK-T, Hoffer-Q, Holladay-1 and Haigis). The residual refractions for the individual target IOL were compared and analyzed. RESULTS: This retrospective study included 42 eyes of 33 patients (age 68.73 ± 10.11 years) after DMEK surgery. The differences between the expected residual refraction based on ray tracing and that predicted with the third-generation formulas were statistically significant (all formulas p < 0.001). The highest mean difference in the residual refraction between the target IOL measured by ray tracing and that calculated with third-generation formulas was found for the Haigis formula (0.90 ± 0.40 D), and the lowest mean difference for the SRK/T formula (0.73 ± 0.49 D). CONCLUSIONS: DMEK surgery induced a relevant change in the anterior to posterior corneal curvature relationship; this needs to be taken into account in the IOL power calculation to avoid hyperopic refractive surprises.