Background
Good unaided distance visual acuity (VA) is now a realistic expectation following cataract surgery and intraocular lens (IOL) implantation Near vision, however, still requires additional refractive power, usually in the form of reading glasses Multiple optic (multifocal) IOLs are available which claim to allow good vision at a range of distances It is unclear whether this benefit outweighs the optical compromises inherent in multifocal IOLs

Objectives
To assess the visual effects of multifocal IOLs in comparison with the current standard treatment of monofocal lens implantation

Search methods
We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) (2016, Issue 5), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to June 2016), Embase (January 1980 to June 2016), the ISRCTN registry (wwwisrctncom/editAdvancedSearch), ClinicalTrialsgov (wwwclinicaltrialsgov), and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (wwwwhoint/ictrp/search/en) We did not use any date or language restrictions in the electronic searches for trials We last searched the electronic databases on 13 June 2016

Selection criteria
All randomised controlled trials comparing a multifocal IOL of any type with a monofocal IOL as control were included Both unilateral and bilateral implantation trials were included We also considered trials comparing multifocal IOLs with "monovision" whereby one eye is corrected for distance vision and one eye corrected for near vision

Data collection and analysis
We used standard methodological procedures expected by Cochrane We assessed the 'certainty' of the evidence using GRADE

Main results
We found 20 eligible trials that enrolled 2230 people with data available on 2061 people (3194 eyes) These trials were conducted in Europe (13), China (three), USA (one), Middle East (one), India (one) and one multicentre study in Europe and the USA Most of these trials compared multifocal with monofocal lenses; two trials compared multifocal lenses with monovision There was considerable variety in the make and model of lenses implanted Overall we considered the trials at risk of performance and detection bias because it was difficult to mask participants and outcome assessors It was also difficult to assess the role of reporting bias

There was moderate-certainty evidence that the distance acuity achieved with multifocal lenses was not different to that achieved with monofocal lenses (unaided VA worse than 6/6: pooled RR 096, 95% confidence interval (CI) 089 to 103; eyes = 682; studies = 8) People receiving multifocal lenses may achieve better near vision (RR for unaided near VA worse than J3/J4 was 020, 95% CI 007 to 058; eyes = 782; studies = 8) We judged this to be low-certainty evidence because of risk of bias in the included studies and high heterogeneity (I2 = 93%) although all included studies favoured multifocal lenses with respect to this outcome

People receiving multifocal lenses may be less spectacle dependent (RR 063, 95% CI 055 to 073; eyes = 1000; studies = 10) We judged this to be low-certainty evidence because of risk of bias and evidence of publication bias (skewed funnel plot) There was also high heterogeneity (I2 = 67%) but all studies favoured multifocal lenses We did not additionally downgrade for this

Adverse subjective visual phenomena were more prevalent and more troublesome in participants with a multifocal IOL compared with monofocals (RR for glare 141, 95% CI 103 to 193; eyes = 544; studies = 7, low-certainty evidence and RR for haloes 358, 95% CI 199 to 646; eyes = 662; studies = 7; moderate-certainty evidence)

Two studies compared multifocal lenses with monovision There was no evidence for any important differences in distance VA between the groups (mean difference (MD) 002 logMAR, 95% CI -002 to 006; eyes = 186; studies = 1), unaided intermediate VA (MD 007 logMAR, 95% CI 004 to 010; eyes = 181; studies = 1) and unaided near VA (MD -004, 95% CI -008 to 000; eyes = 186; studies = 1) compared with people receiving monovision People receiving multifocal lenses were less likely to be spectacle dependent (RR 040, 95% CI 030 to 053; eyes = 262; studies = 2) but more likely to report problems with glare (RR 141, 95% CI 114 to 173; eyes = 187; studies = 1) compared with people receiving monovision In one study, the investigators noted that more people in the multifocal group underwent IOL exchange in the first year after surgery (6 participants with multifocal vs 0 participants with monovision)

Authors' conclusions
Multifocal IOLs are effective at improving near vision relative to monofocal IOLs although there is uncertainty as to the size of the effect Whether that improvement outweighs the adverse effects of multifocal IOLs, such as glare and haloes, will vary between people Motivation to achieve spectacle independence is likely to be the deciding factor

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Multifocal versus monofocal intraocular lenses after cataract extraction

The ReSTOR intraocular lens presents a unique apodized diffractive design within a refractive foldable acrylic optic, which makes an unprecedented level of mulifocal optical performance available. We describe the history and principles of diffractive optics used in the development of this refractive-diffractive IOL.

History and development of the apodized diffractive intraocular lens.

Multifocal versus monofocal intraocular lenses in cataract surgery: A systematic review

Cataract in the Adult Eye Preferred Practice Pattern

Phacoemulsification and modern cataract surgery.

Purpose: To collect clinical data on cataract surgery to allow participating surgeons to compare their performance with that of their colleagues in an anonymous manner. Setting: Surgeons from 31 surgical units providing cataract surgery in 13 European countries. Methods: Every patient at each participating unit having surgery during 1 study month was evaluated. Data were reported to the coordinating center at the time of surgery and at the final examination. When the study was closed 6 months after surgery, all participants were provided with the outcomes from their own patients so they could compare them with outcomes from other centers. Results: The study included preoperative and intraoperative data on 2950 patients. Complete follow-up data were available for 2731 patients. The surgical audit included surgically induced astigmatism, proximity of target refraction, and the frequency of major complications. For each variable, a large variation in outcome between participating centers was found. Most centers had results both above and below average for different variables. Conclusion: Cataract surgery data collected from 31 units in 13 European countries allowed participants to compare their performance with that of their colleagues in an anonymous manner. Significant variation was found in the outcomes among the units, with many units reporting results above and below the averages.

1998 European cataract outcome study: Report from the European Cataract Outcome Study Group

Purpose: To compare a Pharmacia diffractive bifocal intraocular lens (IOL) with a monofocal lens of the same design without the diffractive grating. Setting:. Multicenter study. Methods: This randomized, prospective study comprised 70 patients with a monofocal IOL and 79 with a diffractive bifocal IOL. Follow-up was 5 to 6 months. Near and distance visual acuities, contrast sensitivity, patient satisfaction, and spectacle use were evaluated. Results: All patients achieved a best corrected visual acuity of 0.5 or better; 80% in the monofocal and 71 % in the bifocal group had a best corrected visual acuity of 1.0 or better. Without correction, 93% of the bifocal and 9% of the monofocal group could read J3 or better. With distance correction, 99% and 4%, respectively, could read J3 or better. Contrast sensitivity was slightly lower in the bifocal group at distance and near for all spatial frequencies. In the bifocal group, 46% never used spectacles for near tasks. Overall satisfaction was rated good by 86% of the monofocal and 85% of the bifocal group. Conclusions: The diffractive bifocal IOL performed well at distance and near. Patients who no longer require spectacles will benefit significantly from a bifocal IOL, but many with a bifocal IOL in one eye will require spectacles for the fellow eye.

Comparison of a diffractive bifocal and a monofocal intraocular lens

Purpose: To compare contrast sensitivity (CS) after implantation of a diffractive bifocal intraocular lens (IOL) and a monofocal IOL of similar design. Setting: Seven European centers. Methods: In this randomized, prospective study, CS was tested 5 months after cataract and IOL implantation surgery in 115 patients with a diffractive bifocal IOL and 106 patients with a monofocal IOL. It was also tested in a subgroup of 38 patients who had bilateral implantation of a diffractive bifocal IOL. Contrast sensitivity was tested using the Vision Contrast Test System (VCTS). Results: In patients with a best corrected visual acuity (BCVA) of 1.0 or better, the CS at all spatial frequencies (1.5 to 18 cycles/degree), both at distance and near, was slightly lower in the bifocal IOL group than in the monofocal group. Mean values were within the normal range. In patients with a BCVA of less than 1.0, the CS was lower and the difference between the bifocal and monofocal groups was less. In patients with bilateral bifocal IOLs, CS was better when tested bilaterally than when testing the better eye alone. Pupil size affected the results to a small degree. Contrast sensitivity appeared to improve over time after implantation of a diffractive bifocal IOL. Conclusions: In patients with cataract and no other eye pathology, the diffractive bifocal IOL will slightly reduce the CS at all spatial frequencies. In those with reduced visual acuity after cataract surgery, CS will be reduced accordingly. In this situation, the reduction from the diffractive bifocal optic would be minor.

Eugenio Leite

Papers

1998 European cataract outcome study: Report from the European Cataract Outcome Study Group

Comparison of a diffractive bifocal and a monofocal intraocular lens

Contrast sensitivity after implantation of diffractive bifocal and monofocal intraocular lenses