Polypseudophakia, the concept of using a second intraocular lens (IOL) to supplement an IOL that has already been placed in the capsular bag, was first used as a corrective measure where the power requirement was higher than that of available single IOLs. Subsequently, the technique was modified to compensate for post-operative residual refractive errors. In these early cases, an IOL designed for the capsular bag would be implanted in the sulcus. Although these approaches were less than ideal, alternative means of correcting residual refractive errors were not without their limitations: IOL exchange can be traumatic to the eye and is not easily carried out once fibrosis has occurred, while corneal refractive surgical techniques are not suitable for all patients. Piggyback implantation was the term first coined to describe the use of two IOLs, placed together in the capsular bag. The term was later extended to include the procedure where an IOL designed for the capsular bag was placed in the sulcus. Unfortunately, the term piggyback has persisted even though these two approaches have been largely discredited. Intraocular lenses are now available which have been specifically designed for placement in the ciliary sulcus. As these newer IOLs avoid the many unacceptable complications brought about by both types of earlier piggyback implantation, it is time to employ a new terminology, such as supplementary IOL or secondary enhancement to distinguish between the placement of an unsuitable capsular bag IOL in the sulcus and the implantation of an IOL specifically designed for ciliary sulcus implantation. In addition to minimising possible complications, supplementary IOLs designed for the sulcus have expanded the options available to the ophthalmic surgeon. With these new IOLs it is possible to correct presbyopia and residual astigmatism, and to provide temporary correction of refractive errors in growing, or unstable, eyes. This article aims to review the literature available on supplementary IOL implantation in the ciliary sulcus and to summarise the evidence for the efficacy and safety of this intervention.
Key messages
What is known
Polypseudophakia has been used for over 30 years to correct hyperopia or residual refractive error, but early techniques were associated with significant complications.
What is new
The development of specially designed sulcus-fixated supplementary IOLs significantly reduces the risks associated with these procedures, and has also opened up new opportunities in patient care.
The reversibility of the procedure allows patients to experience multifocality, and to provide temporary and adjustable correction in unstable or growing eyes.
The terms “secondary enhancement” or “DUET” to describe supplementary IOL implantation are preferential to “piggyback”.
Hinweise
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Historical use of polypseudophakia to achieve optical power
In the ‘two-in-the-bag’ technique, first reported in 1993, an additional IOL is inserted in the capsular bag over the existing lens implant (hence the term “piggyback”) to adjust the optical power.[1] Primary implantation of a second IOL was initially used for extreme hyperopia when a single high power IOL was out of the range of manufacturers’ power inventories and those available were inadequate to provide sufficient power.[1, 2] This became unnecessary once manufacturers routinely developed IOLs with higher dioptric power.
In 1999 the first case report emerged of a multifocal IOL being implanted two-in-the-bag with an aspheric IOL (both three-piece silicone) to simultaneously correct hyperopia and improve near vision.[3] This was followed in 2001 by the same technique used in five patients.[4]
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This procedure was used throughout the 1990s but it was discovered that placing two lenses in the bag allowed an avenue for lens epithelial cells to proliferate, resulting in visually significant interlenticular opacification (ILO).[5] It is characterised by opacification in the interlenticular space, caused by Elschnig pearls or membrane formation, resulting in a loss of corrected visual acuity.[6] As ILO is a late complication, the actual incidence is probably higher than that reported.[7]
One of the early reports of ILO took place two years after surgery in 70 eyes, in a study where two IOLs had been implanted, some two-in-the-bag, and some in the bag and the sulcus. Post-operative opacification was found in 23 eyes (32.8%), but only in cases where both IOLs had been inserted into the capsular bag.[5] The interlenticular membrane was easily stripped from between polymethylmethacrylate (PMMA) lenses (two cases) but some acrylic IOLs were tightly fused and could not be separated.[5]
The exact cause of ILO is unknown, but it has been postulated that bioadhesion of the anterior lens to the anterior capsule and the posterior lens to the posterior capsule may prevent cell migration from the equatorial bow to the posterior capsule. This migration may instead be directed toward the interlenticular space, resulting in ILO.[5] Different types of opacification have been reported, with the most common being the formation of Elschnig pearls, thought to arise from retained proliferative lens epithelial cells. In some histopathological examinations following IOL explantation, epithelial cells were mixed with cortical lens material.[5]
There also appears to be a difference in the incidence of ILO related to IOL material: incidence was found to be higher when acrylic IOLs were used compared with PMMA IOLs.[6]
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Although the mechanism is not entirely clear, hyperopic shift can take place when two IOLs are placed in the capsular bag, which may arise from contact between the two optics leading to deformation or flattening, resulting in a lower refractive power.[5, 6] Shugar and Schwarz (1999) reported clinically significant hyperopic shift that emerged between 1 and 2 years after implantation of two IOLs in the capsular bag.[7] All eyes had visible proliferating Elschnig pearls in the peripheral interface between the IOL optics.[7] This phenomenon has not been reported where the second IOL is placed in the ciliary sulcus.
Despite these drawbacks, and the existence of better alternatives, it is surprising that this technique was still being used as recently as 2022.[8]
Options for correction of refractive surprise
Causes of refractive surprise
Since the development in the 1980s of optical biometry using PCI (partial coherence interferometry),[9] and following this, the emergence of SS-OCT (swept-source optical coherence tomography)[10] refractive outcomes have improved considerably with a steadily increasing percentage of patients achieving target refraction. Between 1992 and 2006, around 72 to 87% of patients deviated from target refraction by ±1.0 D, increasing to over 90% in the following ten years.[11] At the same time, between 1996 and 2005, 45 to 58% of patients were within ±0.5 D, increasing to over 61% in the following ten years.[11]
Despite these successes, refractive surprises are still not uncommon. The requirement for a secondary procedure to reduce residual refractive error after refractive lens exchange and multifocal IOL implantation has decreased in the last decade but is still in the region of 3 to 10%.[11]
There are numerous steps involved in cataract surgery any one of which can contribute to refractive surprise.
In the pre-operative stages, biometric data, such as axial length, corneal curvature (refractive power), anterior chamber depth (ACD), lens thickness, white-to-white, can be included to estimate the refractive power of the IOL to be implanted. Small errors in the measurement of biometric data can result in clinically significant refraction errors. Accurate estimation is critical as an error of 0.1 mm in axial length can equate to a post-operative refractive error of around 0.27 D,[12] while an error of 1 mm in ACD can result in an error of 1.44 D.[13] There are limitations to the available IOL power calculation formulae, which tend to work best in eyes with a normal axial length.[14] Aristodemou et al (2011) evaluated the most commonly used IOL formulae and found that only 75% of eyes were within ±0.5 D of target refraction, despite using the optimised A constant.[15]
Mis-estimation of the post-operative IOL effective lens position, broad tolerances in the labelling of IOLs, previous eye surgery, and pre-existing corneal astigmatism (at least 1.0 D in around one-third of cataract surgery patients) all contribute to post-operative refractive error.[14]
Surgical factors such as the size and position of the capsulorhexis are important as is the avoidance of surgically induced astigmatism.[11] Following surgery, rotation, decentration and tilt will affect post-operative outcomes, as will capsular fibrosis and contraction leading to anterior movement.[16]
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IOL exchange for correction of refractive error
In IOL exchange, the primary IOL is removed and replaced with one of the correct power. It is best performed early, before adhesions have formed and used to be preferred over other methods for the correction of large errors.[17] Late removal can lead to complications such as posterior capsular rupture and zonular damage which in turn can lead to cyclodialysis, retinal tears and macular oedema.[18] Damage to the zonulo-capsular complex may prevent fixation of another IOL, possibly requiring additional surgery for a scleral- or iris-fixated or angle-supported IOL [17, 19, 20]
Another drawback with IOL exchange is that it is difficult to estimate the level of correction required without knowing the true cause of the original error. If the refractive issue was due to incorrect IOL power selection, the exact cause must be identified, and the magnitude of the error calculated, if lens exchange is to be performed.[18]
Corneal refractive surgery to correct residual error
Corneal refractive surgery, (or laser vision correction surgery) is a safe, effective, predictable and non-invasive method to correct residual refractive error following cataract surgery,[21] and is particularly applicable when there is stable refractive error, and normal corneal topography.[22] It can be particularly successful when the residual refractive error is myopia.[23, 24] Intrastromal arcuate keratotomy is also reported to achieve good results.[25]
However, laser-based techniques are not as effective as lens-based procedures in the correction of large refractive errors,[24] and there are other disadvantages to this technique. Specifically, laser ablation is not viable in eyes with thin corneas, abnormal corneal topography, corneal scarring or degeneration, or pre-existing HOAs (higher order aberrations).[24] In fact it has been reported that it may induce HOAs[26] and, in rare cases, secondary corneal ectasia.[27] It may not be suitable in an older population with a higher prevalence of dry eye.[28, 29] Other concerns are a higher cost and a lack of reversibility.
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Secondary implantation for correction of refractive error
The use of two IOLs in the eye (polypseudophakia) was initially used to achieve optical power by placing two IOLs in the capsular bag. The concept of using two IOLs rapidly extended to become a technique for correction of refractive surprise, where the second IOL is placed in the sulcus rather than the capsular bag. Although these two techniques are very different, it is unfortunate that the term “piggyback” was also extended to, and came to be associated with, this procedure as well.
Secondary sulcus implantation was seen to be less traumatic than IOL exchange, particularly if the original procedure had been performed some time before, carried a lower risk of complications and produced more predictable refractive results. The capsular bag is preserved and the additional IOL power can be easily calculated based on refraction and vergence calculation, without the need to know the power of the first IOL, or the axial length of the eye.[18] It is effective in reducing high degrees of spherical error, and is reversible.[14, 30]
In one report, compared to IOL exchange, implantation of a capsular bag IOL in the sulcus resulted in 15% more eyes achieving uncorrected visual acuity (UCVA) of 20/20 or better.[18] Ninety-two per cent of eyes that underwent implantation of the additional lens achieved a spherical equivalent refraction within 0.5 D of the intended correction, compared to only 82% of eyes that underwent IOL exchange.[18] Note that the secondary IOL in this case, the hydrophobic acrylic AcrySof MA60MA, was not designed for sulcus implantation.
Compared to laser-based procedures, the implantation of a secondary IOL does not alter the anterior corneal surface or significantly change corneal refractive power,[14] which may provide more precise outcomes,[18] and may be a suitable method for patients with dry eye disease, thin corneas, or keratoconus who are not suitable for laser vision correction.[31]
However, in early reports, IOLs designed solely for use in the capsular bag, such as the AcrySof MA60MA, SA60AT and MA60BM, Storz P359UV, Staar AQ-5010V, were often inappropriately implanted in the ciliary sulcus.[16] There are many reports in the literature of the complications caused by the implantation of a standard capsular bag IOL in the sulcus.[32‐35] These include: pigment dispersion,[36‐38] iris transillumination defects, dysphotopsia, glaucoma,[39] intraocular haemorrhage, cystoid macular oedema, hyperopic defocus and pupil capture.[35, 40, 41]
Following a survey of committee members in 2009, the Cataract Clinical Committee of the American Society for Cataract and Refractive Surgery concluded that: “IOLs designed solely for the capsular bag should not be placed in the ciliary sulcus.[35] The haptics are generally too large, and can contact the posterior iris. They are also planar and do not vault the optic posteriorly from the iris. Finally, most are too small (13.0 mm) which can lead to decentration in a larger eye.”[35]
Sulcus-fixated supplementary IOLs
A welcome development in recent years has been that of supplementary IOLs which have been specifically designed to avoid the complications associated with implantation of a capsular bag IOL in the ciliary sulcus.
The critical features of these IOLs which make them suitable for this application are: hydrophilic acrylic material to optimise uveal biocompatibility, a large optical diameter to avoid IOL capture during pupil dilation, a rounded optic edge to avoid visual disturbances, angulated haptics to reduce the risk of contact with the posterior surface of the iris, a concave posterior optic to avoid the risk of contact between the primary and secondary IOL, and a rounded haptic edge to minimise irritation of the iris, pigmentary dispersion, and secondary pigmentary glaucoma. Implantation of an appropriately designed supplementary IOL in the ciliary sulcus maintains effective distance between the two IOLs, minimising the risk of formation of ILO.[31]
Compared to IOL exchange which must be carried out relatively quickly after the initial procedure, implantation of a sulcus-fixated supplementary IOL, can be carried out years after the primary procedure.[42] As with the implantation of any IOL in the sulcus, power calculation depends solely on the patient’s existing subjective refractive status and not on the pre-operative biometry measurements.[16] As a result, power calculations are likely to be more accurate than for IOL exchange.[43]
The term “DUET” procedure has been suggested by Michael Amon to describe the procedure where a sulcus-designed supplementary IOL is implanted in the ciliary sulcus and a primary IOL is implanted in the capsular bag.[44] The implantations can be carried out in the same procedure, particularly for correction of high myopia or hyperopia, for presbyopia or astigmatism, or sequentially if post-surgical enhancement is needed.
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Extending the applications for supplementary IOLs
The development of appropriately designed sulcus-fixated IOLs has led to an expansion of their uses beyond the correction of residual refractive error after cataract surgery. Note that some of the following applications may be off-label for specific sulcus-fixated IOLs and have been explored by individual ophthalmologists seeking solutions for particular patient problems.
As a primary procedure (DUET): for eyes with extreme refractive error, refractive power can be split between the two IOLs.[22] Any residual refractive error within the available power range of the sulcus-designed supplementary IOL can be treated by exchanging the supplementary IOL.
Eyes with silicone oil in situ: pars planar vitrectomy with silicone oil filling is used to stabilise the retina in complicated retinal conditions. When used as a tamponade agent, silicone oil changes the refractive status of the eye. Once the tamponade is no longer required, and the silicone oil is removed, there is likely to be a refractive shift. Implantation of a supplementary IOL can reduce the problems caused by anisometropia, allow for better UCVA, and can be easily exchanged once the oil has been removed.[22]
Keratoconus: eyes with keratoconus or undergoing keratoplasty often have high astigmatism but may need future procedures in response to changes in astigmatism. A spherical IOL can be implanted in the capsular bag, and a supplementary toric IOL in the sulcus to correct the initial astigmatism. The supplementary IOL can be exchanged if necessary following any repeat procedures.[22]
Presbyopia correction: a monofocal IOL targeted on emmetropia is implanted in the bag and a plano multifocal IOL in the sulcus to correct for presbyopia.[22] In some patients, it can be difficult to predict their tolerance to halo, glare and reduced contrast sensitivity.[45] If the patient cannot tolerate the multifocal optic, the supplementary IOL can be removed and the patient will still remain corrected for spectacle-independent distance vision.[22] This process provides an opportunity for patients to experience multifocality – or trifocality depending on the IOL – while allowing safe and easy removal of the sulcus-based IOL if side effects prove intolerable.[45] Some patients cannot adjust to the multiple images, photic phenomena or reduced contrast sensitivity (CS) of the multifocal optic.
Paediatric applications: IOL implantation in an infant, for example, for aphakia or following trauma, is common, with the aim usually being to achieve emmetropia.[22] But as the child grows, the eye will become increasingly myopic. To counter this, the power of the IOL in the bag is calculated to target emmetropia once the eye is fully grown, while a supplementary IOL can compensate for the intermediate period while the eye is growing.[22] As the eye changes, the supplementary IOL can be removed or exchanged.
Other eye pathologies: patients with cataract at a young age may develop ocular pathologies such as macular degeneration, glaucoma, or retinal detachment, leading to loss of function. Implantation of a multifocal or trifocal IOL in the bag has disadvantages as the condition progresses, but a supplementary IOL can be safely removed, even decades after surgery.[45]
Currently available supplementary sulcus fixated IOLs
Supplementary IOLs are available from the following manufacturers: Rayner (Sulcoflex range), 1stQ / Medicontur (AddOn range), Cristalens Industrie (Reverso), and Morcher (XtraFocus pinhole supplementary IOL). Details are summarised in Tables 1 and 2.
Table 1
Currently available sulcus-fixated supplementary IOLs
IOL
Structure
Material
Optic diameter
Optic features
Overall diameter
Haptics
Angulation
Sulcoflex (Rayner)
One-piece
Hydrophilic + UV filter (Rayacryl)
6.5 mm
Round edges. Concave posterior
14.0 mm
Undulating, rounded edges
10o
AddOn (1stQ)
One-piece
Hydrophilic + UV filter
6.0 mm
Round edges. Convex-concave
13.0 mm
Four flexible closed loops, 0.3 mm thick
0
Reverso (Cristalens)
One-piece
Hydrophilic (Benz 25)
6.5 mm
Round edges. Convex-concave
13.8 mm
Open C loop
10o
XtraFocus (Morcher)
One-piece
Black hydrophobic acrylic
1.3 mm, occluded Sect. 6 mm
Concave-convex
14.0 mm
Undulating, rounded, polished edges
14o
Sulcoflex Technical Information sheets available from Rayner Intraocular Lenses Ltd, 10 Dominion Way, Worthing, West Sussex BN14 8AQ, UK. 1stQ IOL Portfolio data sheets (2024) from www.1stq.de/download. Cristalens Technical Specification available from Cristalens Industrie, 4 Rue Louis de Broglie, 22,300 Lannion, France. XtraFocus technical brochure available from Morcher GmbH, Kapuzinerweg 12, 70,374 Stuttgart, Germany
Table 2
Power ranges for currently available sulcus-fixated IOLs
IOL
Range
Increment
Rayner Sulcoflex
Sulcoflex® Aspheric 700L (formerly 653L)
-5.0 to + 5.0 D (standard range)
0.50 D
Sulcoflex® Toric 710 T (formerly 653 T)
Standard
SE: -3.0 to + 3.0 D
Cylinders: + 1.0 D, + 2.0 D, + 3.0 D
Made to order:
SE: -7.0 to + 7.0 D
Cylinders: + 1.0 to 6.0 D
0.50 D
Sulcoflex® Multifocal 653F (bifocal refractive) with an addition of + 3.50 D. Discontinued in most markets
Sphere from -3.0 to + 3.0 D
0.50 D
Sulcoflex® Trifocal 703F (trifocal diffractive) with a near addition of + 3.50 D, intermediate addition of + 1.75 D
-3.00 to + 3.00 D
-1.00 to + 1.00 D
0.50 D
0.25 D
1stQ AddOn®
Spherical
-0.5 to + 0.5 D
-10.0 to -0.5 D
+ 0.5 to + 10.0 D
0.50 D
0.25 D
0.25 D
Toric
-10.0 to + 10.0 D sphere
+ 1.0 to + 11.0 D cylinder
Progressive (multifocal, EDOF, trifocal), with different additions + 2.25 D; + 3.0 D to mix and match
-5.0 to + 5.0 D
Progressive trifocal-toric with a near addition of + 3.0 D
-3.0 to + 3.0 D sphere
+ 1.0 to + 4.5 D cylinder
SML (Scharioth Macula Lens) addition for ultra-near vision: ARMD
On request
Cristalens Reverso®
Reverso® Monofocal
-6.0 to + 6.0 D
0.50 D
Reverso® Multifocal
Available with different additions of + 1.50 D, + 2.00 D, + 2.50 D, + 3.00 D, + 3.50 D to mix and match
-3.0 to + 3.0 D
0.50 D
ARMD: age-related macular degeneration; EDO: extended depth of focus
Sulcoflex Technical Information sheets available from Rayner Intraocular Lenses Ltd, 10 Dominion Way, Worthing, West Sussex BN14 8AQ, UK. 1stQ IOL Portfolio data sheets (2024) from www.1stq.de/download. Cristalens Technical Specification available from Cristalens Industrie, 4 Rue Louis de Broglie, 22,300 Lannion, France. XtraFocus technical brochure available from Morcher GmbH, Kapuzinerweg 12, 70,374 Stuttgart, Germany
In addition, HumanOptics used to market the Aspira range of supplementary IOLs. These were three-piece silicone IOLs, available as aspheric, toric and multifocal models and achieved good clinical results as reported in a number of studies.[46‐53] This range has now been discontinued and is no longer available.
The Morcher XtraFocus is an opaque disc with a pinhole 1.3mm opening, usually applied for the correction of irregular astigmatism due to keratoconus, pellucid marginal degeneration, perforating corneal trauma, other corneal irregularities or following radial keratotomy or PK (penetrating keratoplasty). The small aperture blocks most peripheral aberrated rays and the pinhole effect can extend the depth of focus which may be helpful for the correction of presbyopia.[54, 55] It is included here for completeness.
A low level of complications has been reported for these four IOLs. These include dysphotopsia, transiently raised postoperative intraoperative pressure, and mild cases of pigment dispersion that did not require treatment. No cases of iris chafing, or ILO were reported.
See Table 3 for a summary of all the studies referred to in this section.
Distance: Mean pre-operative UDVA: 1.09 ± 0.21 logMAR
Mean post-operative: 0.34 ± 0.09 logMAR (p < 0.001) at one year
Near: No significant improvement
One case of significant inflammation
PCO in two eyes
Three cases of decentration requiring repositioning
The Sulcoflex range (Rayner, Worthing, UK)
The Sulcoflex range of supplementary IOLs, see Figure 1 (a to h), has been designed to overcome the disadvantages that arise when conventional capsular bag IOLs are placed in the ciliary sulcus.[16] They are available as monofocal, monofocal-toric and trifocal supplementary IOLs. The bifocal refractive multifocal and multifocal-toric models have been discontinued in most markets.
Fig. 1
The range of Rayner sulcus-fixated supplementary IOLs
×
The one-piece hydrophilic design withstands the stress of implantation through a small incision, minimising haptic damage.[56] It has been reported that three-piece IOLs are more likely to lose their “memory” after implantation, causing a shift of the IOL optic. Although these results were obtained from IOLs placed in the capsular bag,[72, 73] laboratory studies confirm that one-piece PMMA lenses exhibit better loop memory compared to three-piece.[74, 75]
The posterior concave design of the Sulcoflex is intended to minimise contact between the optical zones of the two IOLs. A study using Scheimpflug photography to measure the distance between a primary and the secondary Sulcoflex IOL demonstrated that there was a good distance which was maintained over the course of the study between the two IOLs which will significantly reduce the risk of ILO.[56]
In the same study, ultrasound biomicrography (UBM) was used to assess the distance between the Sulcoflex IOL and the iris-pupil edge. Pigment dispersion can occur when the optic margin or haptics chafe the iris pigment epithelium. The UBM images confirmed that the ten-degree angulation of the Sulcoflex keeps the optic at a safe distance from the iris,[56] and this is confirmed by clinical experience. The undulating design of the haptics may also contribute to the stability of the IOL, optimising centration and rotational stability.[56]
Optical quality
Łabuz et al (2021) used ray-tracing simulations to assess the effect of the position of an aberration-neutral Sulcoflex IOL on visual performance.[76] The Sulcoflex had a nominal power of 1 to 10 D and was positioned with a capsular IOL of 20 D. The optical performance was tested for misalignment through the area under the modular transfer function (MTFa). There was good tolerance to a 1.0 mm decentration with a loss of MTFa of only 2% for the 10 D Sulcoflex. An extreme 10° tilt would result in a 4% reduction of the MTFa for a 10 D sulcus-fixated IOL, with the impact of off-axis position becoming less noticeable in eye models requiring lower-power supplementary lenses. When misaligned, low-power sulcus-fixated IOLs might retain optical quality more efficiently than a high-power capsular-bag lens, but an extreme tilt has a more detrimental effect on performance than a 1.0 mm decentration.
In an optical bench study, Łabuz et al (2020) compared the MTF and US Air Force (USAF) target images of an aberration-neutral Sulcoflex Trifocal (703F) implanted with an aberration-neutral RayOne Aspheric RAO600C monofocal IOL to that of a capsular bag-fixed aberration-neutral RayOne Trifocal IOL (RAO603F, all from Rayner Intraocular Lenses Ltd).[77] Equivalent results were found for both approaches. The presence of two IOLs rather than one led to a minimal light loss of 1.3% through reflection at additional interfaces, material absorption and light scattering.
Stability and clearance
McIntyre et al (2012), using high frequency ultrasound assessment in cadaver eyes already implanted with an IOL in the capsular bag, demonstrated that the Sulcoflex had good centration and minimal or no tilt. The Sulcoflex IOL could be injected and positioned in the ciliary sulcus, giving a clearance between the two IOLs of 232 to 779 µm, depending on the thickness of the primary IOL. The results showed that the design of the IOL minimised the possibility of interaction with the primary IOL and uveal tissues.[59]
Centration
Prager et al (2017) confirmed the stability of the Sulcoflex in 48 eyes of 43 patients.[61] After a mean follow-up of 25 months the mean decentration of the Sulcoflex IOL was 0.23 ± 0.02 mm. The mean decentration of the capsular bag IOLs was significantly greater at 0.29 ± 0.02 mm relative to the limbus.
Kahraman and Amon (2010) implanted the Sulcoflex 700L prospectively in 12 eyes of 10 patients requiring correction of residual refractive error.[56] Correction of refractive error was safe and predictable with an improvement in uncorrected distance VA (UDVA) in all cases. There were no signs of pigment dispersion, iris bulging, foreign body giant cell formation, or ILO. There was one case of minor decentration thought to be due possibly to the eye having a large ciliary diameter and weak zonular support.
In another small series, 15 eyes with relatively high residual refractive errors were implanted with the Sulcoflex 700L (13) and the Sulcoflex 653T, now known as the 710T (2).[58] After a mean follow up of 14 months, there was good visual acuity in all patients and predictable refraction. There was no decentration, rotation or tilt in the aspheric lenses.
Venter et al (2014) report a larger study of 80 eyes that had become ametropic following initial multifocal IOL implantation with the Lentis Mplus MF30.[62] Patients with a refractive cylinder of less than 1.0 D were included, and a Sulcoflex Aspheric supplementary IOL ranging from -2.50 to +4.5 D was implanted. At one year, both sphere and cylinder had reduced significantly with 94% of eyes within ±0.50 D of emmetropia, and statistically significant improvements in UDVA and corrected distance visual acuity (CDVA). Implantation of the supplementary IOL did not affect reading performance of the multifocal IOL.
Key points: a monofocal aspheric supplementary IOL in the sulcus can be used to correct a residual refractive error after the implantation of a multifocal IOL in the bag. The Sulcoflex Aspheric 700L supplementary IOL is stable in the eye with minimal tilt, decentration or rotation. This IOL provides good visual acuity and predictable refraction. Studies have found a low level of complications, particularly relating to ILO and iris touch.
Sulcoflex Multifocal 653F (discontinued in most markets)
Khan and Muhtaseb (2011) successfully implanted four bifocal Sulcoflex Multifocal IOLs and one toric, in five eyes of four patients requiring improvement of their original post-operative vision. All patients had significantly improved UDVA and good uncorrected near VA (UNVA).[43]
Schrecker et al (2014) implanted the bifocal refractive Sulcoflex Multifocal 653F IOL in 35 eyes, and the diffractive MS 714 PB Diff in 33 eyes following implantation of an acrylic IOL in the bag.[51] The IOLs were implanted in a single procedure. At 3 months there was no difference between groups in UDVA or CDVA and both performed well in terms of far, intermediate and near visual acuity. Sixteen out of 19 patients were satisfied or very satisfied with their vision, at all distances and in all lighting conditions. There were more photic phenomena reports in the Sulcoflex patient group but these were mostly rated as mild to moderate. The unfolding process for the Sulcoflex was smoother and more controllable.
The Sulcoflex Multifocal was discontinued in most markets following the launch of the Sulcoflex Trifocal 703F in 2018.
Key points: implantation of the bifocal refractive Sulcoflex Multifocal 653F IOL in the sulcus improves intermediate and near visual acuity.
Falzon and Stewart (2012) report that the Sulcoflex Toric IOL is predictable in adjusting post-operative refractive results and reducing spectacle dependence for distance following surgery.[16] In their retrospective case review of 15 eyes, mostly implanted with the Sulcoflex Toric IOL, all patients were within 1.00 D of attempted correction, and 93% within 0.50 D. Astigmatic error was significantly reduced and there were no significant complications.
In a study of ten eyes, Ferreira et al (2015) implanted the Sulcoflex Toric IOL to correct residual astigmatism.[31] Patients had received an IOL in the capsular bag at least 6 months previously, and the refractive error was stable. Good visual results were obtained in all patients: refractive error was significantly reduced and visual acuity improved. There was a statistically significant reduction in ocular aberrometry values and improved photopic contrast sensitivity. This study also provides evidence for the stability of this supplementary sulcus-fixated toric IOL. At 6 months, mean axis misalignment was 3.0 ± 2.45°. As one degree of rotation can lead to a loss of up to 3.3% of cylinder power,[78] this is considered an excellent result by the authors. In difficult cases, where the IOL persists in rotating, as in, for example, cases of irregular sulcus anatomy, the Sulcoflex Toric can be rotated or fixed with transscleral sutures.[79]
McLintock (2019) carried out a retrospective chart review of the Sulcoflex Toric implanted in 51 eyes, including 19 with a history of corneal grafts, with at least 3 months follow-up.[60] Mean UDVA improved significantly but more so in eyes without corneal grafts. Most patients achieved SE within ±0.5 D of target and cylinder. Sixty-two percent required re-positioning, following this, mean rotation was 6.17°.
Key points: residual astigmatism can easily be corrected with the supplementary Sulcoflex Toric IOL. Studies demonstrated good stability, leading to minimal misalignment and loss of cylinder power. The intervention is particularly useful for patients not suitable for corneal refractive surgery.
Kahraman et al (2021), evaluated 40 eyes of 20 patients implanted with a monofocal IOL in the capsular bag and a supplementary diffractive Sulcoflex Trifocal IOL (703F).[57] All patients required an improvement in their visual acuity and had a desire for spectacle independence. At 6 months, visual acuity was good at all distances and all patients reported full spectacle independence. The IOL provided good levels of functional visual acuity over a wide range of defocus values (-3.00 to +0.50 D). Photic phenomena occurred in some patients but were not disturbing. Mean patient satisfaction was 9.21/10. No adverse events were reported for any patients and there was no rotation or tilt. All implanted supplementary IOLs had a base power of 0.00 D, near addition of +3.50 D and intermediate addition of +1.75 D.
In patients scheduled for cataract surgery or refractive lens exchange, Baur et al (2022) carried out combined implantation of the Sulcoflex Trifocal 703F IOL in 25 patients (48 eyes) with implantation of various IOLs in the capsular bag to achieve reversible trifocality.[45] At 3 months, they reported excellent results for far, intermediate and near vision which are comparable to results reported for capsular bag-fixated trifocal lenses. Monocular defocus curve testing found a visual acuity of 0.2 logMAR or better from +0.75 to −3.5 D. There was one case of decentration which required suturing. All patients who completed the assessment reported halos and more than two-thirds of patients reported glare.
In a case report concerning an 18 year old patient with bilateral hereditary hyperferritinaemia-cataract syndrome, a monofocal IOL was implanted in the capsular bag to achieve emmetropia, and a supplementary trifocal IOL in the ciliary sulcus.[80] The supplementary trifocal IOL can easily be removed at a later stage if necessary. A similar procedure was carried out on a young cataract patient with bilateral central posterior shell opacity.[81]
Key points: The Sulcoflex Trifocal IOL was stable in the eye and provided good levels of functional visual acuity over a range of distances. As is often the case with trifocal IOLs, photic phenomena were experienced by many patients but were generally not disturbing.
The AddOn range (1stQ GmbH, Mannheim, Germany)
The AddOn range of IOLs are single piece devices composed of hydrophilic acrylic. They have four square-shaped haptics and a large optic designed to avoid pupillary capture along with round edges to minimise iris chafing, see Figure 2.[67]
Fig. 2
1stQ AddOn IOL
×
They are available as monofocal-spherical, monofocal-toric, multifocal (bifocal diffractive), multifocal-toric and trifocal, with different power additions including low add, or extended depth of focus versions. The term “AddOn” has sometimes been used loosely in the published literature to mean any supplementary IOL, so caution is needed in interpreting studies to ensure that the IOL is part of the 1stQ range.
Stability
Reiter et al (2017) implanted the 1stQ AddOn supplementary IOL into the ciliary sulcus of 12 cadaver eyes that had previously been implanted with a range of capsular bag IOLs. Assessment with anterior segment optical coherence tomography (AS-OCT) found the AddOn to be well centred in all eyes. Four cases of tilt were seen: three with mild tilt due to pre-existing zonular dehiscence, and one due to a localized area of Soemmering’s ring formation. Mean distance between the two IOLs was 0.68 mm (0.34 to 1.24). Overall the IOL demonstrated proper fixation and centration.[67]
AddOn Spherical / Toric IOL
Gundersen et al (2017) carried out a chart review of 46 eyes implanted with the supplementary spherical or toric AddOn IOL and a variety of primary IOLs. Following implantation of the supplementary IOL, there was a statistically significant improvement in UCVA of about 2 lines, with no change in BCVA and a significant reduction in the absolute magnitude of the residual spherical equivalent refractive error. In the ten cases with a toric secondary IOL, there was a statistically significant reduction in astigmatism. The IOL provides a viable surgical option to correct residual refractive error after primary IOL implantation and performance was unrelated to the identity of the primary IOL.[64]
Gundersen et al (2020) evaluated eighteen eyes with secondary implantation of the AddOn toric supplementary IOL at least one month after surgery. Mean residual refractive astigmatism was significantly reduced. All patients had very good visual acuity. There was little change in orientation since implantation with mean absolute lens rotation of ≤5°: 89% of eyes had a lens rotation of ≤10° and only two eyes had a lens rotation of more than 10°.[65] The authors concluded that lens rotation was minimal.
Key points: the 1stQ AddOn spherical IOL improves visual acuity and reduces residual SE while the toric model can significantly reduce astigmatism.
AddOn Progressive 677MY (Trifocal IOL)
Palomino-Bautista et al (2020) implanted the 1stQ AddOn trifocal supplementary IOL in 18 eyes of 11 pseudophakic patients requiring improved spectacle independence.[42] All patients had previously undergone uncomplicated implantation of monofocal capsular bag IOLs. Of interest is that the mean time after implantation of the primary IOL was 11.4 years. After surgery, 83.3% of eyes had spherical refractions within ±0.5 D of emmetropia and 100% of eyes had spherical equivalent refractions within ±1.0 D of target refraction. Visual acuity and defocus curves confirmed the trifocal nature of the IOL which was superior in intermediate and near ranges compared to a trifocal capsular bag IOL. All patients achieved spectacle independence at all distances. All AddOn IOLs were well positioned in the ciliary sulcus. The authors conclude that the supplementary trifocal AddOn IOL is a safe, efficient and stable solution for achieving spectacle independence in pseudophakic patients.
Albayrak et al (2021) implanted the AddOn trifocal supplementary IOL in a prospective study involving 28 eyes of 18 patients who had been implanted with a primary IOL in the previous year.[63] Mean UNVA improved significantly and results for intermediate VA were good. Twenty-five eyes had a residual SE within 1.0 D of target refraction. Contrast sensitivity was unaffected. All patients had better visual function and quality scores compared to pre-operative values, with the highest improvement being seen in near vision.
Harrisberg et al (2023) carried out a retrospective analysis of patients implanted with a trifocal AddOn (A4DW0M) secondary to implantation of a toric or non-toric monofocal in the bag, comparing the results to those obtained from a single capsular bag multifocal.[66] They concluded that the IOL was effective and safe in correcting distance and near vision and increasing spectacle-independence. There were no significant differences between the groups in any parameter.
Khoramnia et al (2023) performed a laboratory analysis of a trifocal AddOn (A4DW0M) in a polypseudophakic model with a monofocal lens compared to a trifocal IOL (B1EWYN) in the capsular bag.[82] The MTF Strehl ratio was measured, and the USAF-target images were assessed. The polypseudophakic system yielded a better optical quality at far focus, while the standard trifocal provided improved imaging at near distances. The differences arose from different diffractive patterns between the two models; however, visual inspection of the resolution chart did not reveal noticeable image-quality loss confirming the equivalence of the two approaches.
Key points: the AddOn Progressive trifocal IOL from 1stQ provides predictable and stable refraction, good visual acuity at all distances and a high rate of spectacle independence.
Reverso (Cristalens International SAS, Lannion, France)
The Reverso multifocal IOL (see Figure 3) was implanted in a primary procedure along with a capsular bag IOL, into the eyes of 27 patients undergoing cataract surgery, and seeking presbyopia correction.
Fig. 3
The Cristalens Reverso® IOLs
×
[68] At one year, there was improvement in uncorrected distance and near vision, a high level of patient satisfaction and a low level of complications.
XtraFocus pinhole IOL (Morcher GmbH)
The XtraFocus pinhole IOL offers a different approach to correction of residual refractive errors but tends to be used in eyes with high corneal aberration, irregular astigmatism, or large or irregular pupils.
The XtraFocus IOL is composed of black hydrophobic acrylic which blocks visible light but is transparent to infrared light to permit retinal examination. The central section is 6 mm in diameter including the occlusive section, with a concave‑convex design and no refractive power, see Figure 4.
Fig. 4
The Morcher XtraFocus pinhole supplementary IOL
×
In the middle is a central opening of 1.3 mm, and the IOL has an overall diameter of 13.5 mm. The haptics are rounded, polished and undulating and are 250 μm thick to avoid uveal tissue injury and are angulated at 14° to prevent iris chafing and pigment dispersion. The XtraFocus received the CE mark in 2016 and is commercially available in several countries.[54]
Applications
In patients with clear central corneas, the Xtrafocus can neutralise high amounts of corneal aberration and extend the depth of field for presbyopia correction. Patients with significant dysphotopsia from multifocal IOLs or severe glare and light sensitivity from irregular or large pupils may also benefit.[54] The device is helpful in pseudophakic patients with irregular astigmatism causing significant visual impairment,[70] and can also be beneficial in patients with large iris defects.[71]
Secondary indications are near or intermediate vision enhancement in pseudophakes with monofocal IOLs, and dysphotopsia reduction in eyes with multifocal IOLs.[69]
Clinical studies
There are a limited number of clinical reports for the XtraFocus. Trindade et al (2017) implanted the XtraFocus to correct irregular corneal astigmatism in 21 patients with significant visual impairment due to keratoconus, radial keratotomy or penetrating keratoplasty, traumatic corneal laceration, post‑LASIK ectasia, and eccentric excimer laser ablation. There was marked improvement in visual function and high patient satisfaction following surgery.[70]
Ho et al (2022) implanted the XtraFocus in 11 patients with irregular corneal astigmatism, or with iris trauma. The device was implanted at the same time as a capsular bag IOL, but all XtraFocus IOLs were implanted in the sulcus. The procedure was effective at improving vision or reducing glare but two patients had to have the device explanted because of severe glare.[69]
The XtraFocus was implanted in 32 eyes of 16 patients with irregular corneal astigmatism and BCVA worse than 20/50 in both eyes. Patients had undergone surgery either for clear lens exchange or due to cataract. The IOL was found to be safe, and effective, bringing about significant improvement in visual acuity.[71] Note: in just over half of the cases, both primary and supplementary IOLs were implanted in the capsular bag. The results for the two procedures are not reported separately.
A publication in 2020 reported a retrospective study of 60 eyes implanted with the device to treat irregular corneal astigmatism.[83] However, in this study, the device was implanted in the capsular bag alongside a variety of other IOLs so will not be considered here. The authors state that this IOL is less stable in the sulcus compared to placement in the capsular bag.
To summarise, IOLs designed for use in the ciliary sulcus have been specifically designed to overcome the disadvantages that arise when conventional capsular bag IOLs are used in this way.
Important features of the Sulcoflex range are a posterior concave design to minimise contact between the optical zones of the two IOLs and sufficient angulation of the haptics to keep the optic at a safe distance from the iris. The AddOn range employs a different design with four square-shaped haptics and a large optic intended to avoid pupillary capture. Rounded edges on the haptics are a common feature of both IOLs to minimise iris chafing. The XtraFocus supplementary IOL is a pinhole device intended for the correction of irregular residual astigmatism and other more specialist applications.
Both main IOL ranges have demonstrated proper fixation and centration, and one study confirmed better centration of the Sulcoflex platform in the ciliary sulcus compared to IOLs implanted in the capsular bag. However, there is insufficient published data on the Reverso IOL to reach a conclusion on stability, and one study on the XtraFocus suggested it was less stable in the sulcus.
The Sulcoflex monofocal aspheric supplementary IOL can be used to correct residual refractive errors after implantation of other IOLs in the bag, providing good visual acuity and predictable refraction. The bifocal refractive Sulcoflex Multifocal 653F IOL improves intermediate and near visual acuity, while the Sulcoflex Trifocal IOL provides good levels of functional visual acuity over a range of distances. Photic phenomena are experienced by many patients but in both cases the procedure is easily reversible if the patient cannot adjust. Residual astigmatism can easily be corrected with the supplementary Sulcoflex Toric IOL which has demonstrated good stability, leading to minimal misalignment and loss of cylinder power.
The 1stQ AddOn spherical IOL improves visual acuity and reduces residual SE while the toric model significantly reduces astigmatism. The AddOn Progressive trifocal IOL provides predictable and stable refraction, good visual acuity at all distances and a high rate of spectacle independence.
Power calculations for supplementary IOLs.
Unlike implantation into the capsular bag, it is a very simple process to find the appropriate power for a supplementary IOL, depending on the refractive target. If the target is emmetropia, all that is required is the patient’s current and stable subjective refraction (spectacle prescription). There is usually no need for biometry data or other complex measurements. It is also not necessary to know the power of any IOL in the capsular bag: the optical power of the supplementary IOL is simply calculated based on the existing subjective refraction of the optical system.
In pseudophakic patients, supplementary sulcus fixated IOLs are usually required in relatively low powers, therefore, deviations from the optimal lens positioning should be of limited clinical relevance and importance.[45]
Each manufacturer has provided online calculators, specific to each IOL which can be found on the individual manufacturer’s website. The following links were correct at the time of going to press:
Alternatively, Amon et al (2023) recommended a simple calculation method:
• R-vergence formula: spherical equivalent (SE) of ametropia, K-values, ACD
• Post-operative ametropia within ± 7.0 D
o
Hyperopia: spherical equivalent (SE) × 1.5
o
Myopia: spherical equivalent (SE) × 1.2
Although emmetropia is the most common aim, targeting myopia with the capsular bag IOL can be useful when aiming to correct presbyopia with a multifocal or trifocal supplementary IOL.[84] In Myopic Multifocal Duet Implantation (MMDI) the target refraction of the primary capsular bag–implanted IOL can be set at approximately −2.5 D to optimise the refraction for near distance should the supplementary IOL be removed at a later date.[85]
The MMDI approach was used for two of 25 patients in a recent study.[45] The RayTrace Premium IOL calculator was used for the supplementary sulcus-fixated Sulcoflex IOLs, targeting for emmetropia to compensate for the myopic target refraction of the primary IOL. The target refraction of the capsular bag–fixated IOL was emmetropia in the 23 other cases and a supplementary sulcus-fixated IOL with plano power was therefore selected.
Conclusions
The term “Piggyback IOL” should ideally not be used any more to describe the use of two IOLs in the eye, as it originated as a description for procedures that are associated with many potentially serious complications: the two-in-the-bag approach, and the implantation into the ciliary sulcus of an IOL designed for the capsular bag.
“Supplementary IOL implantation” is the preferred term for the addition of a second IOL which has been specifically designed for implantation in the ciliary sulcus, to an eye that has another IOL in the capsular bag. The two implantations may be carried out sequentially or in the same procedure. Other terms in use are DUET procedures or secondary enhancement. Critical design features include a concave posterior surface of the IOL to maintain distance between the two optics, and angulated haptics that minimise contact with the iris.
Implantation of an appropriately designed supplementary IOL is safe and effective as a means of correcting residual refractive error. The reversibility of the procedure can also offer the surgeon many other options for patients, such as reversible trifocality, refractive correction in patients with temporary tamponades or with ongoing ocular pathologies, and in developing eyes.
Acknowledgements
We would like to thank Jude Douglass, Healthcom Partners, Oxford, UK for assistance in research, drafting and editing the manuscript. We would also like to thank Rayner, Worthing, UK for an unrestricted grant that allowed this work to be funded.
Declarations
Ethical Approval.
Not applicable for a review paper.
Informed consent.
Not applicable. No human patients were involved in this review paper
Research involving human participants and/or animals.
Not applicable. No human participants and/or animals were involved in this review paper.
Disclosures of potential conflicts of interest
Ramin Khoramnia reports grants, personal fees, and non-financial support from Alcon, Johnson & Johnson, Hoya, Physiol, Rayner, personal fees, and non-financial support from Kowa, Ophtec, Oculentis/Teleon, Santen, and Acufocus, outside the submitted work.
Michael Amon is a consultant to Rayner Intraocular Lenses Ltd.
Gerd U Auffarth reports grants, personal fees, non-financial support and consulting fees from Johnson & Johnson and Alcon, grants, personal fees, and non-financial support from Carl Zeiss Meditec, Hoya, Kowa, Oculentis/Teleon, Rayner, Santen, Sifi, Ursa-pharm, grants and personal fees from Biotech, Oculus, EyeYon grants from Acufocus, Contamac, Glaukos, Physiol and Rheacell, outside the submitted work.
Guenal Kahraman, Grzegorz Łabuz and Isabella D Baur certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.
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