Multifocal IOLs provide a new horizon of possibilities in presbyopia correction. The Restor IOL (Alcon Laboratories, Inc., Fort Worth, Texas), an apodized diffractive multifocal IOL with optic concentric steps that diffract light in smaller waves, is an extremely interesting option.1-4 Emmetropia to minimal hyperopia is the best optical strategy for final refraction with the Restor.1 Surgeons must be aware that patients will perceive halos around point sources of light at night, and neural adaptation, mostly if the implant is binocular, will diminish perception of this problem with time.
In our experience, the Restor is an outstanding IOL, however, a cautious and organized approach is recommended to obtain the best results. Most importantly, precise IOL centration is mandatory.5,6 A decentered Restor lens provides a worse performance than a well-centered one, in which all steps work on the visual axis. Residual refractive defects may be induced by imperfect centration, and patients with diffractive multifocal IOLs poorly tolerate these defects.
It is important to remember that the center of the pupil and the line connecting it with the fixating object (ie, line of sight [LOS]) are not always coincident with the visual or optical axis. As a matter of fact, mean distance between the center of the pupil (LOS) and the visual axis (angle kappa) is 2.6º horizontally and 0.6º vertically. Furthermore, the center of the pupil shifts during myosis or mydriasis. Thus, centering a multifocal IOL in the bag in a fully dilated eye does not mean centering it on the pupil, and the pupil center may not be coincident with the visual axis.
THE PROCESS
Preoperative evaluation. Ideally, the visual axis, pupil center, and IOL center must coincide. We presently exclude patients with a very distant visual axis and pupil center, as well as those patients with very distant pupillary centers in miosis versus mydriasis. The whole situation can be verified preoperatively with a combined topographer-aberrometer based on patient fixation (OPD-Scan; Nidek, Inc., Gamagori, Japan), also providing the total, internal, and corneal ocular aberrations. Evaluating the topography and excluding the map visualization, it is easy to visualize if the pupil is centered with the topography rings, and thus with the visual axis. Furthermore, the OPD-Scan provides information pertaining to pupil centration on the cornea (optical axis). The pupil diameter and center in miosis and mydriasis will also be measured.
Another suggested exam is biometry with the IOLMaster (Carl Zeiss Meditec AG, Jena, Germany). This device provides precise determination of the visual axis length, reducing operator or indenting probe bias, with patient fixation constantly present in all measurements. In our personal experience, however, we integrate IOLMaster information with topography-derived keratometry readings (ie, the mean pupillary power derived from 4,000 topography measurements points).
Intraoperative centration. Ideally, the IOL must be centered on the visual axis, and since this can not be determined intraoperatively, once the preoperative examination has defined that it is almost coincident with the center of the pupil and thus with the LOS, the referral structure is the myotic pupil. The ideal rhexis is a well-centered, 5-mm anterior capsule opening, and obviously capsule rupture must be avoided. The surgeon must accurately center the IOL in bag, remove the viscoelastic, check the centration again, and finally inject a miotic.
When the pupil is 3 to 4 mm, the surgeon must align the IOL rings with the miotic pupil. In cases of even minimal decentration on day 1, the IOL must be immediately recentered with the pupil in miosis. If recentration is necessary, this must be pursued by IOL rotation instead of simple shift or tilt. Usually, despite physiological postoperative fibrosis, the haptics will keep the IOL in this final position (Figure 1).
Clinical case. Figure 2 presents OPD evaluation of an eye with a decentered Restor. The patient complained of poor vision and ghost images. OPD maps with total aberrations showed a considerable amount of aberrations. Internal higher-order aberrations were elevated, and coma was the main component. Figure 3 presents the same eye after recentration. Total, internal, and higher-order aberrations were markedly reduced. Figure 4 presents the difference between internal aberrations preoperatively, immediately postoperative with IOL decentration, and after recentration. A differential internal aberrations map clearly shows induction of coma by the imperfectly centered IOL. Note how preoperative and final internal aberration maps are similar. Following recentration, the patient's vision improved, and he did not refer to ghosting of images anymore. We have recentered two out of 56 implanted IOLs (4.0 %).
Fabrizio I. Camesasca, MD, is the Vice-Chairman of the Department of Ophthalmology, Istituto Clinico Humanitas, Milano, Italy. Dr. Camesasca states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +39 02 8224 2311; fax +39 02 8224 4694; or fabrizio.camesasca@humanitas.it.
Paolo Vinciguerra, MD, is the Chairman of the Department of Ophthalmology, Istituto Clinico Humanitas, Milano, Italy. Dr. Vinciguerra is a member of the CRST Europe Editorial Board. He states that he has no financial interest in the products or companies mentioned. He may be reached at paolo.vinciguerra@humanitas.it.
