Comment on: Influence of ocular biometric parameters such as effective lens position, keratometry, and axial length on near add power of multifocal intraocular lens.

Abstract

We read with interest the manuscript by Wu et al.1 The authors conduced a review about the variability of multifocal intraocular lens (mIOL) addition depending on biometric eye parameters, compiling the theoretical background provided in the scientific literature. The main clinical implication is that this variability should be considered in surgical planning, as the authors remark in the conclusion. Beyond the theoretical background, which was already described by Savini et al.,2 the review missed some important clinical evidence for translation to real practice in mIOL selection. We would like to give our point of view about some important messages for clinical practice and comment on the possible corrections needed. “In clinic, myopic patients with steep cornea often have longer effective lens position (ELP), which reduces near focal point of mIOLs, whereas hyperopic patients with flat cornea have the opposite situation.” This situation is not commonly observed in clinical practice. Patients with a longer axial length (AXL) have a longer ELP, and corneal power is inversely correlated with AXL, which means that eyes with a longer AXL usually have flatter corneas, contrary to the authors' sentence. Thus, the formula considering all the parameters should be used for a correct estimation of the addition (EA) because the higher EA due to lower corneal power is usually dominated by a lower EA due to a longer ELP in longer eyes.3 Wu et al. state: “A larger ELP should be more suitable for a higher near add power of mIOLs and a lower ELP should be more suitable for a higher near add power of mIOLs.”1 We assume the authors based this recommendation on the study by Savini et al., but there is a mistake in the second half of the sentence, which we believe should read: “…lower ELP should be more suitable for a lower near add power of mIOLs.”2 Wu et al. state: “They also found that variations in ELP had a greater effect on the position of the near focal point than K.”1 This is true, the ELP dominates the EA in comparison with keratometry (K), but other factors should be considered beyond the EA calculation. According to clinical evidence, near vision goes beyond the EA. Keratometry has demonstrated frequent relationships with near vision performance, whereas relationships between EA and near visual performance could depend on mIOL design.4 Wu et al. state: “Considering that the defocusing curve can roughly reflect the real near addition of mIOLs,….”1 Clinical evidence supports that EA could underestimate the effective addition calculated from defocus curves.5 In conclusion, beyond the EA calculation for mIOL selection, near vision could be influenced by other eye biometric parameters and mIOL optical characteristics (such as light distribution). Some clinical evidence has demonstrated that eyes with higher corneal power (steeper corneas related to short eyes) have lower areas under the visual acuity defocus curve in the near range.4 Therefore, although the theoretical basis of EA recommends low-addition mIOLs for short eyes, our clinical studies suggest that caution should be exercised when selecting low-addition mIOLs in short eyes in patients with higher expectations of spectacle independence. The theory of EA for mIOL selection is more valid if the same optical design is used for different additions; however, different additions come from different manufacturers and optical designs. Surgeons should consider that EA theory might not always be accomplished. In addition, it should not be forgotten that selecting a higher EA for improving near vision might also lead to poorer intermediate vision, and nowadays, decisions should be made considering patient needs throughout the entire range of vision.