Accuracy of IOL power calculation formulas in patients with FECD

Preoperative corneal pachymetry recommendations have been expanded to less strict criteria, and more FECD patients are being considered for isolated cataract surgery without combined endothelial transplant, according to research presented at the XXXV Congress of the ESCRS in Lisbon, Portugal. Pedro Gil, University of Coimbra, Portugal, presented the results of a retrospective, case-control study of 46 eyes comparing the accuracy of the SRK/T, Barrett Universal II and Hill-RBF formulas in FECD patients and in controls. Mean preoperative central corneal thickness was 613 microns. “Non-optimised Barrett II and the Hill-RBF resulted in a slightly myopic mean prediction error in FECD patients. After optimisation, all three formulas performed similarly in FECD patients, but accuracy is poor and refractive surprises common,” he said. This is because disease-induced corneal thickening and consequent posterior corneal curvature flattening are not considered by the formulas. This decreased posterior steepening increases corneal power, resulting in a myopic shift. This might not be too great of a problem, however, since endothelial keratoplasty tends to result in a hyperopic refractive shift, either due to a concave donor corneal lenticule or dehydration of the transplanted cornea back to a physiological state. This shift can reach 1.50D for DSAEK and a more modest 0.5D shift for DMEK.