Multifocal Intraocular Lenses

To the Editor: I commend Munoz et al on their well-designed and well-conducted study on the clinical effect of a combination of multifocal intraocular lenses (MIOL) including the newest rotationally asymmetric MIOL, which appeared in the March 2012 issue of the Journal of Refractive Surgery.1 They found that contrast sensitivity was comparable to that achievable with a monofocal implant and, remarkably, 92.5% of patients were spectacle-independent for all distances, with a mean postoperative spherical equivalent within 0.50 diopters (D) of emmetropia in 89% of cases. This is notably superior to the benchmark standards set only a few years ago for refractive outcomes after cataract surgery, suggesting that at least 55% of patients should be within 0.50 D of emmetropia.2 The authors should also be praised for providing details regarding the A-constant value and the formula used for IOL power selection. Regarding the mildly myopic mean postoperative spherical equivalent obtained with both lenses, I question whether the authors chose the IOL power with the closest value to emmetropia and whether they believed that fi nal mild myopia would be preferable. Also, given that they used the SRK-T formula in all cases, and no axial length range values were provided, would the authors recommend the employed formula even for eyes shorter than 22.0 mm, which is not recommended by the Royal College of Ophthalmologists guidelines in the United Kingdom.3 Understanding that the authors randomized the eyes receiving the fi rst of the two MIOLs, perhaps collecting information regarding ocular dominance would have allowed a better interpretation of the obtained results. It seems that having had a rotationally asymmetric IOL in one eye helped overcome some of the drawbacks of the diffractive MIOLs, such as moderate halos and insuffi cient intermediate visual acuity. The sample size was relatively small (40 patients), and the randomization process may have resulted in dominant eyes being chosen to receive the rotationally asymmetric MIOL, which had been previously found to allow superior intermediate visual acuity and induce less photic phenomena.4 Gianluca Carifi , MD London, United Kingdom