INTRODUCTION

Presbyopia correction through the implantation of a multifocal lens after refractive lensectomy is an effective and safe procedure. The overall improvement in visual and refractive outcomes as well as procedural safety observed over the last decade is mainly due to two factors: the innovations in the surgical procedure and the technological advances of the available intraocular lenses. However, intraocular lens implantation is also associated with possible side effects or optic complications, which may alter the intended visual outcome or decrease patient satisfaction after the procedure. The main complications or alterations observed are the presence of dysphotopic phenomena (halos and glare), decreased contrast sensitivity and the inability to achieve satisfactory independence of glasses1-3. Dysphotopsia, particularly halos, are mainly associated with the use of diffractive type lenses and are more intense the greater the addition present in the lens. The development of asymmetric refractive optical principle lenses was considered an effective way of eliminating the main disadvantages of diffractive lenses, showing results in contrast sensitivity curves and blur curves equal to or greater than diffractive lenses4-7. The need however, to incorporate the correction of astigmatism in the intraocular lens is very evident, and the presence of residual astigmatism is one of the main causes of unsatisfactory visual outcome after surgery8. The efficacy and safety of asymmetric refractive toric lens implantation has recently been published9,10, and personalization of the lens toricity, namely in the Mplus® model (Oculentis GmbH, Germany), is even higher than in conventional diffractive models.

SECTORAL REFRACTIVE LENSES

According to the previously described, the main disadvantages attributed to diffractive lenses are the presence of dysphotopic optical phenomena (halos and glare) and the reduction of contrast sensitivity. The implantation of an asymmetric sectoral refractive lens, in this case Mplus® (Oculentis), has been shown to reduce the incidence of these optic phenomena and thus improve visual quality after implantation7. In terms of refractive and visual results, the asymmetric refractive lens implant allows obtaining very satisfactory distance, intermediate and near vision acuities, allowing a high independence of glasses7,11-13. On the other hand, combining lenses with different additions for near allows you to customize the binocular end result to the specific needs of each patient.

Some studies reported an increase of internal optical aberrations after implantation of Mplus® sectoral lens, and in particular the increase in coma (3rd order optical aberration of Zernicke) associated with the presence of an asymmetric sector of high refractive power in the lower part of lens14,15.This aberration induction can affect optical quality and decrease contrast sensitivity. In a study by Rosa et al6, it was possible to demonstrate that when compared to a diffractive bifocal lens, the Mplus® lens presents identical visual and refractive results. However, it showed poorer behavior in contrast sensitivity tests in photopic and meso-scotopic conditions for intermediate spatial frequencies. No differences were observed in the behavior of the two lenses at visual acuity level under glare stimulation nor for color vision. However, it has recently been studied and demonstrated in optical bench that, after all, there seems to be no increase in optic aberrations after sectoral refractive lens implantation, especially vertical coma16.

The Mplus® lens is available in two versions: one in C-Loop and one in plate.

A single available study compares the two versions, including a third group of patients with a C-Loop lens and a capsule tension ring17. The collected data points to a better refractive performance of the lens with a plate design, including a lower induction of internal optical aberrations in the in-plate lens group. However, the C-Loop lens with capsular tension ring obtained significantly better visual results on the defocus curve compared to the other two groups of patients.

The same authors had previously published a comparative study between the same lens (Lentis Mplus® LS-312, Oculentis GmbH), with and without a capsule tension ring18. The results show better refractive performance (better sphere predictability, spherical equivalent and subjective refraction) in the postoperative period in patients whose lens is implanted together with the intracapsular distension device, as well as better visual at intermediate distances in the measurement of the defocus curve. No differences were observed in the level of internal aberrations between the two groups.

The orientation of the lens after implantation is another factor of discussion and controversy. The first published studies (with excellent visual and refractive results) show results regarding the inferior-nasal placement of the near-addition segmental zone as recommended by the manufacturer19.

However, the first description about the temporal-superior placement of the near-addition segment demonstrates that the subjective and objective results are identical to the traditional orientation of the lens20, and some isolated cases demonstrate that positioning the near sector in the temporal-superior position can reduce the incidence of dysphotopsies due to an increase in the surface area of ​​the vision zone for distance exposed to the pupillary diameter, subjectively and objectively improving the results in the dominant eye21,22.

Other authors, carrying out a study of visual quality measured in contrast sensitivity and MTF curves in an optical bench, were able to demonstrate significant differences between the distance quality of vision between different positions of the lens in the capsular bag, while at intermediate distances and near these differences were not significant23.

AVAILABLE Mplus® LENS MODELS

The Mplus® lens (Oculentis GmbH, Germany) was the first asymmetrical refractive model available for implantation. Several studies demonstrate visual and refractive outcomes, as well as the degree of satisfaction demonstrated by patients. It is a lens made of hydrophilic acrylic material with a hydrophobic protective outer surface (Benz25 UV material), initially available as a folding and bi-convex C-Loop, with a total diameter of 11.0 mm. The optical design has a 6.0 mm diameter, being refractive and rotational asymmetric: a central aspherical zone dedicated to the vision for far and a peripheral sector region (in the form of meniscus) dedicated to the near vision, with variable additions of +3.0 D or +1.50 D (Figure 1 and Table 1).

Refractive lenses traditionally have two segments, one for distance vision and the other for near vision. The centering of the lens in the capsular bag acquires in these lenses a paramount importance, since the decentration causes a change in the proportion of correction far/near.

This change directly affects uncorrected vision for near and far. For this reason, it has been previously studied and demonstrated that in asymmetric refractive lenses, the implant of a capsular tension ring allows a more adequate lens centering and consequently improves visual and refractive results17,18.

On the other hand, the pupillary diameter of the patient also affects the far-near ratio offered by the lens, and patients with small pupils (below 3.00 mm) are poor candidates for implantation of asymmetric refractive lenses type Mplus®24,25. In order to overcome these optical limitations attributed to asymmetric sectoral refractive lenses, Ophtec developed a segmented refractive multifocal lens, which is independent of the pupillary diameter and the respective centering. The lens has 11 segments, 5 for distance and 6 for near vision (Figure 3).

The segments are distributed in such a way that the possible decentration of the lens or the reduced pupil diameter have a minimal effect on the ratio of the correction between distance and near.

Optical bench tests demonstrate high lens independence from the observed variations in pupillary diameter and lens offset from the pupil.

In 2017 the authors participated in a European clinical trial for validation of the Precizon® Multifocal CTF lens in transparent lens and/or cataract surgery. At the congress of the Portuguese Society of Ophthalmology (December 2017), the joint results of the clinical trial performed in two centers in Portugal were presented: Hospital de Braga and Hospital da Luz - Lisbon. This prospective study included patients undergoing cataract surgery or clear lens extraction, with bilateral implant of the Precizon® Presbyopic lens. The studies included 20 eyes from 10 patients who were evaluated at 3 months postoperative for subjective refraction, distance visual acuity without and with correction (UDVA and CDVA, respectively), intermediate visual acuity without and with correction (UIVA and DCIVA, respectively), near visual acuity without and with correction (UNVA and DCNVA, respectively), contrast sensitivity, presence of dysphotopsies and blurring curve. The postoperative spherical equivalent was 0.00 ± 0.38 D, revealing excellent refractive predictability (Figure 4).

In visual terms, the lens has fulfilled the requirements of a refractive lens for presbyopia treatment: high independence of glasses and excellent visual results. The binocular UDVA was 0.04 ± 0.08 logMAR, the binocular UIVA was 0.16 ± 0.14 logMAR and the UNVA was 0.31 ± 0.16 logMAR. Contrast sensitivity obtained results within normality and comparable with other multifocal lenses (Figure 5).

In Table 2 the results are compared with those available (unpublished) by Ophtec and for the clinical trial that allowed the approval of the lens in the European agencies.

The defocus curve (Figure 6) of the Precizon® Presbyopic lens presented plateau up to -2.00 D (50 cm), with a discrete loss of near-distance vision, just like all lenses of similar depth of focus.

The prevalence of moderate to severe dysphotopsies was less than 5%, and the vast majority of patients did not present any dysphotopic phenomena to report (Figure 7).