Intraocular lens power adjustment nomogram after laser in situ keratomileusis

To develop a nomogram for improving the accuracy of intraocular lens (IOL) power calculation at the time of cataract surgery based on the manifest refraction spherical equivalent (MRSE) change produced by laser in situ keratomileusis (LASIK).

University-based clinical practice, Jules Stein Eye Institute, Los Angeles, California, USA.

This was a retrospective review of the records of consecutive patients who had cataract surgery after LASIK. Spherical equivalent refractive data before and after LASIK and cataract surgery were recorded. The differences between the targeted postoperative refractive errors after cataract surgery and the achieved refractive errors were plotted against the LASIK-induced MRSE change, yielding postoperative refractive errors to target during IOL power calculation to achieve emmetropia.

Thirty-two eyes of 23 patients were identified; 25 eyes had myopic LASIK and 7, hyperopic LASIK. Regression analysis yielded the following polynomial relationship: target postoperative refractive error (D) to achieve emmetropia during IOL power calculation = -0.018(MRSE Change)(2) + 0.192(MRSE Change) - 0.062. The outcomes in 97% of eyes fell within +/-1.00 D of the value predicted by this formula.

A 2nd-order polynomial relationship was found between LASIK-induced MRSE change and the MRSE error after cataract surgery. From this equation, a simple adjustment nomogram was generated and put into a look-up table format. The formula and nomogram should improve IOL power calculation accuracy in post-LASIK eyes when the MRSE change is known.