Piggyback Intraocular Lenses

We would like to comment on case reports and an editorial that deal with piggyback intraocular lenses (IOLs). The editorial1 contains a short summary of our case report on the contact zone of piggyback acrylic IOLs and also discusses a potential multifocal gain that could be achieved with these IOLs. To avoid confusion, we would like to clarify something concerning the latter. In our case report, we suggest there is a second focus caused by the flatter contact zone between the IOLs. This second focus would, however, lie behind the retinal plane. Therefore, this “inverse bifocal IOL” could be beneficial to the patient under only 2 circumstances: The patient wears (+) lenses to correct the central contact zone for distance, or the patient ends up myopic after surgery because of inaccuracies in biometry, power calculation, or both. This would allow the patient to view distance through the central contact zone and near through the peripheral noncontact area of the IOLs. However, it is still unclear how large such a contact zone has to be to enable satisfactory visual acuity. The editorial includes a slitlamp photograph of 2 plate-haptic piggyback IOLs and describes the findings as “a pearl disrupting the optical continuity” of the IOLs. We interpret the findings as a contact zone surrounded by a fine “membrane-like” ring. The contact zone contains a slightly smaller zone of inhomogeneous appearance. We have also seen such changes with silicone piggyback IOLs. They can be found immediately after surgery and do not seem to change with time. We think this inhomogeneous zone is caused by debris (maybe partly traces of viscoelastic material) that becomes trapped between the IOLs, within the contact zone, during surgery. This would explain why it is not washed away by irrigation/aspiration at the end of surgery or by circulating aqueous during the first few postoperative days. The clear zone just outside this inhomogeneous zone is probably the result of a slight enlargement of the contact zone as a result of capsule shrinkage, forcing the IOLs together, during the first few postoperative months. Later, the membrane-like ring forms at the border of the contact zone, possibly a first sign of opacification. In the case report by Shugar and Schwartz,2 a late hyperopic shift in 6 eyes in 3 piggyback patients with interpseudophakos Elsching pearls in interpreted in 3 ways or possibly as a combination: proliferating pearls displacing the posterior IOL backward, a change in zonular tension displacing the entire IOL/capsule complex backward, or pearls proliferating under the capsulorhexis resulting in posterior displacement of both IOLs. The range of hyperopic shifts in the 6 eyes is 2.00 to 4.75 diopters (D). To achieve a hyperopic shift of more than 4.00 D, the IOLs would have to move backward significantly, in 1 of the cases by more than 1.50 mm, as the authors point out. We would like to add a fourth possible explanation. Since we have seen a contact zone with all piggyback IOLs that we have implanted, we infer that most, if not all, the 6 eyes also have central contact zones. If this is the case, the reduction in visual acuity peripheral to the contact zone because of the pearls results in the patient using the central contact zone for subjective refraction. Since this zone is flatter than the surrounding zone, the refraction will be more hyperopic. In 3 eyes with acrylic IOLs (AcrySof MA60BM), we found a refraction difference of 3.0 to 5.5 D between the central contact zone and the peripheral zone (unpublished data). This would provide a simple explanation of the strong hyperopic shifts the authors have seen.