Trifocal and extended depth of focus intraocular lenses – comparative analysis

INTRODUCTION

Cataract is the major cause of vision impairment on a global scale [1], therefore cataract surgery is constantly develop-ing, both in the surgical technique and in the technology of intraocular lens production. Along with the development of civilization, we observe increasing expectations of patients related to the improvement of the quality of life and visual acuity at various distances without the use of corrective glasses [2-4].
Intraocular implants can be divided into so-called “Standard” monofocal and “Premium” lenses. Monofocal lenses are the most commonly implanted lenses in the world. They correct the spherical defect and provide very good visual acuity at one target distance, but for the remaining patients require the use of eyeglass correction [5-7]. The “Premium” group lenses also enable the correction of astigmatism (toric lenses) and presbyopia (multifocal lenses) [8].
In the recent past, the most commonly used multifocal intraocular lenses (IOLs) were the bifocal ones, which provide good and very good vision for near and distance [9]. Their disadvantage, especially in the day of common usage of smartphones and computers, is insufficient visual acuity at intermediate distance [10]. In recent years, trifocal lenses have become widely used, they also allow good or very good intermediate vision [11-15]. The common disadvantage of multifocal lenses, related to the division of light passing through the optical part of the lens into several foci, is the occurrence of undesirable optical phenomena (e.g. glare and halos) and a reduction in contrast sensitivity [16-20]. In order to reduce dysphotopsia while maintaining good quality of vision, extended depth of focus (EDoF) IOLs were introduced on the market. Their design and technology differs between the models of individual manufactures, they can use different principles: spher-ical aberrations, chromatic aberrations or “pinehole effect”, but the main goal of the entire group is common – to achieve “pseudoaccommodation” [21, 22]. They are intended to ensure a very good distance and intermediate visual acuity with an acceptable level of near vision and a low level of dysphotopsia, but the results obtained so far are varied and ambiguous in this regard.
The aim of this article is to present the results of available comparative studies after the implantation of trifocal lenses and lenses with extended depth of focus, taking into account visual acuity at different distances, contrast sensitivity, defocus curve, spectacle independence, reading speed and the presence of optical phenomena. We also analyzed the available previ-ous reviews [23, 24], but our article takes into account the results of partially other authors and, additionally, the aspect of micromonovision in the context of the analyzed lenses.
Trifocal intraocular lenses
Trifocal lenses provide good or very good quality of vision at all distances (Figure 1A). Technologically they are based on the principle of diffraction and they are composed by diffractive microstructures in concentric zones [4]. In some models, the principle of apodization is additionally used. The principle of apodization was based on the greater need for distance vi-sion in condition of dim illumination (when pupils are large). In addition, a greater focus of light to the distant focal point reduces the defocused near light with its subsequent visual phenomena of glare and halos. This is achieved by a gradual re-duction in diffractive step heights from center to periphery [3, 25, 26]. Since 2010 there are several models of these lenses available on the market, the most frequently described in the literature are presented in Table I [27-30].
Extended depth of focus intraocular lens
Extended depth of focus intraocular lenses (EDoF IOLs) are intended to provide a very good distance and intermediate vi-sion acuity with an acceptable level of near vision. The construction and technology of the lenses differ from each other, de-pending on the individual company (Table II). They can use various of principle: spherical aberrations, chromatic aberrations or the “pinehole effect” [21, 22]. Based on the IOL technologies EDoF can be divided into two main categories: pure EDoF and hybrid EDoF. Pure EDoF IOLs employ solely spherical aberration-based optics or “pinehole” effect. Hybrid EDoF IOLs could be categorized as diffractive-EDoF, refractive-EDoF and diffractive-refractive-EDoF IOLs [21]. However, the basic principle of EDoF lenses is to create a single elongated focal point to enhance the depth of focus or range of vision (Figure 1B) [31]. A proprietary diffractive echelette design is used in EDoF IOLs and create their characteristic stepped structure. The height, spacing and profile of the echelettes are optimized to achieve a design in which the light from different zones of the lens mix, thus creating a new light diffraction pattern. In addition, proprietary achromatic technology and negative spherical aberration correction improve the image quality [32].

RESULTS

Characteristics of the included studies
The characteristic of the included studies are summarize in Table III [33-42]. These studies were conducted in different countries. All studies were published between 2017 and 2021. Our analysis included 967 eyes. The Tecnis Symfony IOL was implanted in the eyes included in the EDoF group, whereas PanOptix, FineVision Micro F and AT LISA tri 839 MP IOLs were implanted in the eyes included in the trifocal group. The follow-up duration of the studies ranged from 1 to 29 months.
Visual Outcomes
The results of binocular visual acuity at different distances are presented in Table IV [33-42]. Visual acuity for distance was statistically significant in only one article, according to de Medeiros et al. patients with implanted EDoF IOLs achieved a better final UDVA and CDVA compared to patients with trifocal IOLs [39]. At 60 cm UIVA trifocal lenses was significantly better according to Lubiński et al. [40]. In the range of 66–70 cm de Medeiros et al. and Webers et al. achieved better results in patients EDoF lenses [39, 42], in Monaco’s et al. and Lubiński’s et al. study – with trifocal lenses [33, 40]. At 80 cm UIVA was better for trifocal lenses according to Lu-biński et al. [40], while in the article of Mencucci et al. patients with EDoF lenses achieved better results, but only in mesopic condition, which was also confirmed in the CIVA study in 80 cm [38]. According to all studies, UNVA and CNVA unanimously fared better in the group of patients with trifocal lenses.
Contrast sensitivity
Eight articles [33-38, 40, 42] described contrast sensitivity (CS) (Table V), most of which showed no significant differences between groups [33-35, 37, 42]. In the work of Mencucci et al. EDoF lenses achieved better results in CS than trifocal lenses, both un-der photopic and mesopic conditions [38].
Escandon-Garcia et al. presented the results in which EDoF IOLs perform better under mesopic conditions but only at fre-quency of 1.5 cycles per degree (cpd) [36]. In our study from 2020, the results were as follows: under photopic conditions there were no differences at distance, at near to frequencies of 12 and 18 cpd, the better results were in the trifocal IOLs group; under mesopic conditions – for near there were no differences found, for distance – at the frequency of 18 cpd, EDoF lenses performed better [40].
Defocus curves
Eight articles used the defocus curve as the criterion [33-40, 42] (Table VI). Analysis of the results presented in the table shows that trifocal lenses exhibit better close-range vision acuity compared to EDoF IOLs [33, 34, 36, 37, 39, 40, 42, 43]. In contrast, in the case of distance and intermediate vision acuity, patients with EDoF lenses achieve better results [36, 39, 40, 43], except one work, Monaco et al., in which trifocal lenses also performed better intermediate vision [33, 43]. Cochener et al. found no significant differences between the groups [35].
Photic phenomena
In most studies, the presence of photic phenomena was assessed subjectively by patients, without using standardized scales. For this reason, the results and conclusions presented by the authors may differ from each other. The occurrence of photic phenomena such as halo and glare has been discussed in 9 articles [33-35, 37-42] (Table VII). Most of authors summarize the patient-assessed incidence and severity of dysphotopsia as low in both groups of lenses, but the range is < 1% to 25% [33-35, 39-41]. In 2 articles, Mencucci et al. and Webers et al., the evaluation of the presence of halo/glare was high – from 31% to 70% [38, 42]. Additionally, it can be seen that regardless of the type of implanted lens, halo is more common than glare is reported by patients.
Spectacle independence and reading speed
Six studies provided data for spectacle independence of far, intermediate and near distance [33-35, 38, 40, 42] (Table VII). To distance and intermediate distances, independence from glasses was achieved in 100% of patients in most of analyzed studies [34, 35, 38, 40, 42]. However, according to Monaco et al. 2 patients from the EDoF group and 3 patients from the trifocal lens group declared that they sometimes need distance glasses [33]. For near vision scores were high for both lenses, but the trifocal lens fared slightly better here – an average of 79.83% of patients with EDoF lenses and 87.0% of patients with trifocal lenses achieved independence from glasses.
Reading speed after implantation of both lenses was reported in 2 studies, none of which showed any significant differ-ences [38, 42].
Patient satisfaction
Patient satisfaction after intraocular lens implantation was assessed using various questionnaires. Despite the different methods, the results of the articles are similar. Patients regardless of their implanted lens rate their degree of satisfaction as high and would choose the same lens again [33-35, 38-42] (Table VII).
Micromonovision
A new strategy for EDoF IOLs, called micromonovision, has recently been proposed. It is reported to provide significantly better intermediate and near visual acuity than after implantation of EDoF IOLs targeted for non-monovision [44].
In Cochener et al. study (35) both trifocal IOLs were targeted for emmetropia and the EDoF lens was targeted for mi-cromonovision (< –0.25 D) or emmetropia. Their results showed that UNVA was statistically better for both trifocal lenses as compared to EDoF IOL. Nevertheless, near vision with the EDoF lens was good, however authors suggested this is only the case if targeting slight monovision.
In the article published by Webers et al. [42] the trifocal group was targeted for emmetropia as a postoperative mean re-fractive spherical equivalent and the EDoF group was targeted for micromonovision (–0.5 D) in nondominant eye and emme-tropia in dominant eye. No significant differences were found in the UDVA and UNVA in photopic conditions. A small signifi-cant difference was found in UIVA between both groups in favor of the EDoF group. No differences in visual acuity at all dis-tances were seen between groups under mesopic conditions.
Tan et al.’s [45] patients were divided into two groups: the monovision group and the control group (non-monovision group). In the monovision group, Tecnis Symfony IOL power calculations were performed using a micromonovision approach aiming for minimal residual myopia (≈ −0.50 D) in the nondominant eye and emmetropia in the dominant eye. In the control group, emmetropia was considered as the target refraction for both eyes. There was no statistically significant difference in binocular UDVA between the groups. In contrast, binocular intermediate and near visual acuity was statistically significantly better in the monovision group compared to the control group.
In Cochener’s article for the Concerto Study Group [44] the mean binocular decimal UDVA after bilateral EDoF IOLs (Tecnis Symfony) implantation was comparable in the entire cohort – the monovision group (target refraction between –0.5 D and –0.75 D), and the non-monovision group (target refraction – emmetropia). The monovision group had significantly better UIVA and UNVA than the non-monovision group. Corresponding to these visual outcomes, the level of spectacle independ-ence reported by patients was high, with most eyes not requiring spectacles for distance vision, intermediate vision, or near vision activity. Spectacle independence for near activities was better in the monovision group.
Ganesh et al.’s [46] results were consistent with those of the recently published multicentric study by the Concerto Group, in which bilateral implantation of the EDoF IOL (Tecnis Symfony) with micromonovision provided significantly better uncorrected intermediate and near visual acuity compared to that with the non-monovision group. Their conclusion was that the preliminary results with relatively small number of enrolled eyes suggest that micromonovision with the EDoF IOL was well tolerated and led to excellent outcomes for most activities at all distances. However, further research involving a larger sample size is required to verify these results.

DISCUSSION

In recent years, newer IOL technology has revolutionized cataract surgery to meet patients’ growing expectations for ex-cellent distance, intermediate and near vision [47].
Our article is an up-to-date comparative analysis of the results after implantation of trifocal and extended depth of focus IOLs, which may provide important information in choosing the proper lenses for patients. Regarding visual acuity, the studies results which were analyzed showed significantly better UNVA and CNVA for trifocal than EDoF lenses, while the EDoF group showed slightly better results for UDVA, UIVA and CIVA (Table IV), what was confirmed by the defocus curve (Table VI). In addition, a trifocal lens is more likely to be spectacle independent, but also has a slightly higher potential to induce halo or glare (Table VII).
All studies in this analysis involved bilateral implantation of the same IOLs [33-42]. Most authors declare the preoperative assumption of emmetropia [33, 36, 38, 40, 41]. In articles published by Cochener et al. and Webers et al., patients with tri-focal lenses were achieved target emmetropia, and the EDoF group – emmetropia or micromonovision [35, 42].
The insertion of EDoF lenses compared to trifocal lenses did not fully meet the expectations of patients. In principle, they were supposed to improve the contrast sensitivity, reduce the frequency and intensity of photic phenomena such as glare and halo, while maintaining very good visual acuity in the range from intermediate to the far distances. Our analysis shows that the definitive advantage of EDoF lenses in these categories has not been achieved, so we are waiting for new lens tech-nologies or improvement of the current ones to obtain a lens with good visual acuity at all distances with no or minimal dysphotopsia.
Hence, in order to achieve satisfactory outcomes for near vision, the time-tested concept of micromonovision following the bilateral implantation of this lens may be attempted [48]. Nevertheless, the weak point of micromonovision is the possibility of calculation mistakes, even when using modern calculation formulas.
Despite of all authors adopted similar inclusion and exclusion criteria for the studies, the limitation of our analysis is the differences in the research carried out, such as follow-up time, various methods and conditions for testing e.g., contrast sensitivity or different types of questionnaires assessing the subjective feelings of the patients.
In conclusion, visual function results are very good and comparable for both analyzed types of IOLs. Trifocal lenses pre-sented better near vision, but EDoF IOLs had a slightly lower frequency and severity of photic phenomena. Based on data from the literature, we have not demonstrated a significant superiority of one lens over the other. In clinical practice, still, in addition to the characteristics of the IOL, the patient’s personality, expectations, preoperative status and economic status should also be considered. Also, it makes sense to introduce micromonovision as a refraction target for patients planning to implant EDoF lenses to increase their postoperative satisfaction with vision at intermediate and near distances. In the future, next studies on a larger group of patients with longer follow-up are necessary to demonstrate the superiority of EDoF lenses over trifocals.

DISCLOSURE

The authors declare no conflict of interest.

References