Accommodating Intraocular Lenses
David Varssano, MD
An accommodating intraocular lens (IOL) is associated with a dynamic increase in dioptric power with an effort to refocus from distance to near or to intermediate vergence.1,2 Ideally, a true accommodating IOL has a single focal point in a static position, similar to a traditional monofocal IOL. The ability to see well at different distances emerges solely from physical changes in the lens as a result of the accommodative effort of the person implanted with the lens. A truly accommodative IOL has the potential to create a clear and sharp retinal image, unlike multifocal IOLs, which create multiple images, and serve as the best replacement for the aging crystalline lens. As discussed later, to achieve the goal of dynamically changing optical power, several methods were suggested. Some designs were brought to market, and some are still being used. As seen later, the full promise of the accommodating IOL is still to be delivered.
Nonaccommodating factors such as miosis and induction of higher order aberrations may enhance depth of field, improving intermediate and near vision in both accommodating and monofocal IOLs. Some of the visual benefit of accommodating IOLs is based on pseudoaccommodative factors, as patients cannot discriminate between true accommodation and pseudoaccommodation. Subjective pushup tests or defocus curve determination may frequently overestimate the objective measures of amplitude of accommodation.1,3
PRINCIPLES OF ACCOMMODATING INTRAOCULAR LENSES
There are several principles of accommodating IOLs aimed to produce change in the optical power of the IOL through the patient’s accommodative effort (Table 10-1). Small space constraints, forces, and movements the normal eye uses for natural accommodation forced lens designers to be innovative, leading them to incorporate various fields of science.
Hinge or lever IOLs use the contraction and relaxation of the ciliary muscle to produce accommodation by moving the IOL forward, directly or through posterior vitreous pressure, causing a myopic refractive change to improve near vision. The lens itself is not being deformed. Single-lens versions are a popular lens design.4–9
Dual-lens design (doublet) IOLs use a combination of 2 juxtaposed lenses, whose combination produces the desired IOL power. When mathematically evaluating the ability to produce accommodation with movement of the lenses,10 it appears that a single moving lens is more efficient in terms of diopters (D) per mm of motion than a combination of plus lenses, while a combination of a front plus and a back minus lens is most efficient. The larger the front plus lens power and the more negative the back minus lens power in the combination, the higher the efficiency. Leng et al10 calculated that for a 20.0-D combination, to achieve a 3.0-D add, a single lens would move 2.479 mm, a +10.0 D and +10.0 D combination would move 5.122 mm, and a +45.0 D and a -25.0 D combination would move 0.949 mm.
The concept of refilling the emptied capsular bag with an optically elastic material is the basis for fluid or gel models. Polysiloxane11,12 and silicone oil13 were suggested as candidate materials for this purpose. More investigation is needed to form a complete solution, including a means to empty the capsular bag, fill it, and seal it.
A biomimetic accommodating IOL using a deformable liquid balloon has been proposed.14 A balloon inserted into an emptied capsular bag through a small peripheral capsulorrhexis is filled through a valved detachable tube with a high refractive index fluid (n = 1.4). Previously presbyopic human cadaver eyes were able to accommodate between 2.0 D to 7.4 D after lens implantation.14
A proposed method involved membranes to block capsulorrhexis.15 A membrane was placed in the capsular bag of young monkeys behind the capsulorrhexis and silicone oil injected behind it through a preplaced hole in the membrane.13 Accommodation of 2.0 D to 3.0 D was recorded in response to pilocarpine 4% eye drops.
Another gel-based design consists of a flexible gel contained in a small chamber attached to the eye wall in a fixed position.16–18 As the ciliary muscle constricts, flexible gel is pushed through a round hole to form a bulging lens. Tested in human eyes,16 pilocarpine could induce 10.0 D of accommodation in that design. Flow of silicone oil between hollow haptics and the optic is a similar concept. Change of optic curvature creates accommodation. Such lenses were examined upon rabbits.19,20
Deforming the interface between 2 fluids or gels with forces available in the ciliary body can achieve acceptable accommodation. Two groups used this principle for their designs.21,22
Changing the shape of the IOL using more rigid materials has been proposed using 2 designs. In a sliding-type IOL23 composed of 2 optical elements, the elements slide over each other, changing their composite optical power by 1.27 D ± 0.76 D with accommodation stimulus. A rotating focus mechanism24 around an axis that is parallel to and decentered from the optical axis demonstrated 8.0 D of accommodation in a lab setting.
A voltage-controlled accommodating IOL made of an ionic polymer metal composite actuator was tested in vitro to deform an attached lens.25
In a prototype-based liquid-crystals, accommodation could be produced by changing the refractive index with no moving parts.26
ACCOMMODATING INTRAOCULAR LENSES: PAST AND PRESENT
Early Attempts
Miller27 first discussed the concept of accommodating IOLs in the 1980s. By the end of the decade, monofocal IOLs were tested using A-scan ultrasound and an anterior movement was measured during accommodation. The movement was by 0.7 mm6 for single-piece silicone plate haptic lenses and 0.20 to 0.25 mm for standard looped IOLs.28 In 1990 and 1992, Hara and colleagues reported on the spring IOL.29,30 It consisted of two 6.0-mm optics, held apart by 4 flexible loops. Accommodative effort was supposed to move the lenses apart to create a refractive change. The lenses were built and implanted in rabbit eyes.
Cumming and Kammann31 published the first report of clinical experience with an accommodating IOL in human eyes in 1996. The first lenses were implanted in cataract patients in early 1991. Using pilocarpine drops and a defocus technique, the authors were able to measure an average of 2.75 D (range 1.25 D to 3.5 D) accommodation in one lens design. They confirmed the lens motion using A-scan measurements.
The next attempt was the BioComFold IOL, a single-piece accommodating hydrophilic acrylic IOL with an overall disk-shape configuration and a single optic flanked by 2 semicircular ring haptics.32 Its overall length is 10.0 mm and its biconvex optic is 5.8 mm. A peripheral bulging ring was connected to the optic via an intermediate, forward-angled (10-degree) perforated ring section. To achieve an accommodative effect, the curvature of this disc IOL must move forward. The lens was implanted in human eyes in 1997.4 It allowed greater forward shifts than monofocal IOLs, but failed to produce pseudoaccommodation amplitudes greater than the control standard IOL group. Years later, some of these lenses became opacified with calcification of the lens material.33,34
1CU Accommodating Intraocular Lens
The 1CU accommodating IOL was tested and popularized in Europe. The 1CU IOL is a single-piece biconvex foldable hydrophilic acrylic posterior chamber IOL. It has a 5.5-mm diameter spherical optic, a 9.8-mm total diameter, and 4 haptics.5 It is made of a hydrophilic acrylic with an ultraviolet inhibitor and has a refractive index of 1.46. The lens has a biconvex square-edged optic and 4 modified flexible haptics that bend when constricted by the capsular bag after ciliary muscle contraction. This allows anterior displacement of the optic.35 The first human use of the 1CU IOL was reported in 2001,36 on 6 eyes of 6 patients.
In another trial, 30 patients received 1CU in one eye and a monofocal control in the other. In the 20 available for evaluation, accommodation induced a small anterior movement of the 1CU (0.010 mm ± 0.028 SD). Pilocarpine 4% induced a forward movement of 0.220 ± 0.169 mm in the 1CU compared to a backward movement of 0.028 ± 0.095 mm with the monofocal lens.37 The amount of the IOL shift was not sufficient to provide useful near vision, but the difference suggests that the engineering concept behind the 1CU IOL is valid.
Eighteen months after bilateral implantation in 30 patients,38 distance-corrected near visual acuity (DCNVA; logMAR) was 0.57 ± 0.12 compared to the control monofocal IOL 0.69 ± 0.12 (P = .043). The difference between the 1CU and monofocal control group means were 0.46 D for subjective near point and 0.32 D for defocusing.
Four years after implantation in 12 eyes of 8 patients, DCNVA (logMAR) was 0.50 ± 0.25 while corrected distance visual acuity was -0.10 ± 0.06.5 The mean subjective accommodation amplitude assessed using a D’Acomo dioptric accommodator (World Optical Corp Ltd) at 4 years was 1.36 D ± 0.89 D. The mean objective accommodation amplitude measured using an AA-1 accommodation analyzer (Nidek Inc) was only 0.68 D ± 0.49 D.
Capsular block syndrome was reported with the 1CU,39 and successfully treated with YAG (yttrium-aluminum-garnet) laser anterior capsulotomy.
Crystalens
The Crystalens AT-45 (eyeonics Inc, now Bausch + Lomb) hinge/lever silicone accommodating IOL was first reported in 20016 while being examined by the Food and Drug Administration (FDA). This lens received US FDA approval in November 2003 for correction of aphakia. FDA approval for correction of presbyopia following cataract extraction and to provide near, intermediate, and distance vision without spectacles was obtained in August 2004.40 It is a biconvex lens with a 4.5-mm optic and flexible hinged-plate haptics that allow forward movement of the optic during accommodative effort. The lens design incorporates hinges across the plates adjacent to the lens optic that allow for forward and backward movement of plate-haptic lenses against the vitreous face.
When the Crystalens AT-45 was tested for FDA approval,40 it was implanted in 415 eyes of 263 patients and followed for 1 year. Near visual acuity was measured at 40 cm with the distance correction. Intermediate visual acuity was measured at 80 cm with distance correction. Combined uncorrected distance and uncorrected near visual acuity of 20/40 or better was achieved by 78.8% of eyes and 96.7% of patients at 1 year.
Near acuity measured through the distance correction was 20/25 or better in 24.8% of eyes, and 20/40 or better in 90.1% of eyes at 1 year.
Best-corrected distance visual acuity of 20/25 or better was achieved by 97% of eyes and 20/40 or better was achieved by 99.2% of the eyes. The DCNVA with the Crystalens HD (Baush + Lomb) is marginally better (P = .05) than with a monofocal IOL.41 In contrast, DCNVA with the Crystalens AT-45 was J3 (Jaeger) or better in more than 60% of 25 operated eyes in an uncontrolled study.42
When tested in 20 eyes of 10 patients with anterior segment optical coherence tomography (OCT),43 the Crystalens AO did not shift systematically with accommodative effort, with 9 lenses moving forward and 11 lenses moving backward (under natural conditions). The average shift under stimulated accommodation with pilocarpine was -0.02 ± 0.20 mm. When IOL movement was measured by partial coherence interferometry after 2.0 D stimulation, pilocarpine and cyclopentolate, the conclusion was that the mechanism of action of the Crystalens HD IOL was not primarily from IOL movement.44 The Crystalens HD did not change the refraction with accommodative effort in a group of 10 patients.45
The Crystalens HD 500 accommodating IOL also had decreased distance image quality and slightly increased depth of focus compared with the monofocal IOLs because of the bispheric design.46 Cases of Z syndrome were reported with the Crystalens (AT50SE, AT52SE, and AT-45) after uneventful cataract surgery. Neodymium:YAG laser capsulotomy treatment can resolve the complication.47,48
Dual-Optic Accommodating Intraocular Lenses
Sarfarazi Elliptical Accommodative IOL was licensed by Bausch + Lomb in 2003.49,50 It is formed by 2 optic lenses of 5.0 mm in diameter connected by 3 haptics, which produces accommodation through anterior displacement of the anterior optic. Its elliptical shape has been designed in order to conform to the natural morphology of the crystalline lens capsule. The lens induces an increase in accommodative amplitude of approximately 6.0 D in primates, and was predicted to induce 4.0 D in humans. There are no studies in the literature showing the effectiveness of this IOL in humans.
At the same time the Crystalens was being investigated, a dual-optic accommodating IOL model was produced and placed in a cadaver eye in 2003.51 A similar lens design, now named the Synchrony dual-optic accommodating IOL, was placed in rabbit eyes in 200452 and implanted in human eyes by 2006.53,54
Synchrony Dual-Optic Accommodating Intraocular Lens
The Synchrony dual-optic accommodating IOL49 has 2 optical lenses located within the capsular bag. The haptics are placed in the sulcus. It is available in powers ranging from +16.0 D to +28.0 D in steps of +0.5 D with a total length of 9.5 mm and 9.8 mm wide. The +32.0 D anterior optical lens has a diameter of 5.5 mm and is connected through the spring haptic to the 6.0-mm negative-powered posterior optical lens. The haptics of the Synchrony dual-optic accommodating IOL were designed to permit a displacement of 1.5 mm of the anterior optic with the ciliary body contraction. The Synchrony dual-optic accommodating IOL has had CE approval since 2006. It can be injected through a 3.8- to 4.0-mm incision, depending on the dioptric power.
In a prospective noncomparative case series,54 23 of 24 eyes (96%) had 20/40 or better DCNVA. In a prospective multicenter clinical study with Synchrony Vu (Johnson & Johnson Vision)55 on 74 patients (148 eyes), clinical data at 6 months showed 89% of the eyes within ±1.0 D planned spherical equivalent refraction. Mean binocular uncorrected and corrected distance visual acuity was 20/20 at far, 20/20 at intermediate, and 20/25 at near. Mesopic contrast sensitivity was within normal limits. Seventy-eight percent of the patients had no spectacles. Dysphotopsia was present at 30%. One eye had IOL repositioning within 1 month of surgery. Good distance-corrected near reading ability at 40 cm of 0.07 logMAR was maintained for at least 2 years.56 Aberrometry while using an accommodative stimulus of 3.0 D revealed accommodation of approximately 1.0 D with a pupil size of 3.0 mm 4.5 years postoperatively.57
Comparison between a single-optic accommodating IOL (Crystalens HD) and a dual-optic accommodating IOL (Synchrony) in patients after cataract surgery concluded that both IOLs restored distance visual function after cataract surgery with limitations in near visual outcomes. Eyes with the dual-optic IOL had significantly better ocular optical quality.58
Pars plana vitrectomy for epiretinal membrane removal was performed in the presence of a Synchrony dual-optic accommodating IOL.59 During pars plana vitrectomy, visualization of the macula was described as perfect.
NuLens
Ben-Nun and Alio17 first reported in 2005 of a new lens design, later to be named NuLens. This lens consists of a flexible gel contained in a small chamber attached to the eye wall in fixed position.16,18 A piston operated by the empty, collapsed capsular bag pushes the contained flexible gel through a round hole to form a bulge that functions as a lens; the steeper the bulge, the stronger the lens. As the ciliary muscles respond to the naturally occurring retinal-brain blur stimulus, they apply force to the piston via the capsular diaphragm. This force deforms the silicone gel curvature until the best image is achieved on the retina at any given distance, creating a dynamic high-power lens. A clinical report of the NuLens implanted in 10 patients with atrophic macular degeneration was published in 2009.16 Pilocarpine induced changes in ultrasound biomicroscopy cross-section of the IOL and the measured best reading distance suggest that the lens could achieve 10.0 D of accommodation.
Tetraflex
Human implantation of another lens design, the KH-3500, was first reported in an article published in 2006.60 The KH-3500 IOL, later named Tetraflex,7 is a single-piece, spherical, acrylic IOL with refractive index of 1.46. The central optic portion is 5.75 mm and the overall size 12.0 mm in diameter.60 It has a flexible haptic that is designed to allow the whole lens to move anteriorly in the capsular bag secondary to ciliary muscle contraction, unlike the hinged haptics in other designs. The KH-3500 has limited objective accommodating effects.
In a prospective, age-matched, nonrandomized FDA clinical trial, Tetraflex was compared to a control monofocal IOL.61 Seventy-five percent of the Tetraflex patients reported near spectacle wear either never or only occasionally for small print and/or dim light (21% never) compared with 46% of control patients (P < .001; 9% never) at 1 year postoperatively.
In a noncontrolled study of 50 eyes implanted with the Tetraflex,62 the mean subjective accommodation was 0.94 D and mean pilocarpine-induced IOL mobility was 337 μm. In 28 participants implanted with the KH-3500 monocularly, accommodation was 0.39 D ± 0.53 D measured objectively using the SRW-5000 (Shin-Nippon Commerce Inc) through undilated pupils and was 3.1 D ± 1.6 D measured subjectively with a Royal Air Force binocular gauge (Clement Clarke/Haag-Streit).60
The Tetraflex appeared not to move forward upon accommodation63 when examined with an anterior segment OCT. Near vision benefits may be due to changes in the optical aberrations because of the flexure of the IOL on accommodative effort.
In a series of 95 eyes of 59 patients implanted with the Tetraflex,7 89.3% achieved a DCNVA of 20/40 or better at 6 months after surgery.
Patients implanted with Tetraflex IOL had better DCNVA and greater amplitude of accommodation (1.99 D ± 0.58 D vs 1.59 D ± 0.45 D, P < .05) compared with the control group that had nonaccommodating IOLs.64
When measured with a spectral-domain OCT at relaxed and maximal accommodative states, the Tetraflex showed a forward movement in 69.6%, more than in the control group (P < .001). However, the authors concluded that the slight forward axial shifts of the Tetraflex IOL during natural accommodation may not produce a clinically relevant change in optical power.
Tetraflex was used in a study on 24 patients.64 At 3 months, uncorrected distance visual acuity (logMAR) was 0.26 ± 0.14, best-corrected distance visual acuity was 0.22 ± 0.11, uncorrected near visual acuity was 0.27 ± 0.15, and DCNVA was 0.24 ± 0.12. Subjective accommodation (D) measured with a defocus method was 1.54 ± 0.39 and objective accommodation (D) measured with the Optical Quality Analysis System (Visiometrics) was 1.27 ± 0.41 (0.75 to 2.25). Forward movement measured with anterior segment OCT (Visante-1000, Carl Zeiss Meditec) was 130.46 ± 42.71 μm.
In 2016, Li et al64 reported a good correlation between lens shift induced by pilocarpine before surgery and postoperative IOL shift under accommodation stimulus, subjective accommodation, and objective accommodation, following implantation of the Tetraflex IOL. This is a new predictive factor for surgical success with accommodative IOLs.
In a retrospective study comparing Tetraflex, a refractive multifocal IOL (ReZoom; Abbott Medical Optics, now Johnson & Johnson Vision), and a diffractive multifocal IOL (ZMA00; Abbott Medical Optics, now Johnson & Johnson Vision),65 no statistically significant differences were found in uncorrected and corrected distance visual acuity and uncorrected intermediate visual acuity among the groups (P = .39). The Tetraflex had similar distance-corrected intermediate visual acuity as the other lenses. It had significantly worse near visual acuity than the ZMA00 group (P < .05). Better contrast sensitivity values were observed in the Tetraflex group under most of the spatial frequencies conditions (P = .025). The total aberration was lowest in the ZMA00 group (P = .000), and the spherical aberration was highest in the Tetraflex group (P = .000). The 3 groups had similar frequency of ghosting and glare, and the Tetraflex group had a lower rate of halos (P = .01).
An in-the-bag subluxation of the hydrophilic acrylic Tetraflex accommodating IOL following capsulorrhexis phimosis was reported.66 Explantation of the IOL-capsular bag complex was required 7 years after implantation. Histopathologic analysis demonstrated multiple areas of thick anterior subcapsular fibrosis and pseudoexfoliative material.
Tek-Clear
Another single-optic design, the Tekia Tek-Clear,50,67 has been approved for treatment of presbyopia by the European Commission since 2006. This accommodating hydrophilic acrylic IOL has symmetric optic design, ultraviolet blocker, and square edge design. Patients using the Tek-Clear lens achieved DCNVA of 0.25 ± 0.23 logMAR as opposed to 0.49 ± 0.1 with a standard monofocal lens (P < .001).67
Other Developmental Lenses
It has been suggested that since the refractive power of a lens is derived from its physical shape and refractive index, changing the refractive index would create an accommodating lens that has no moving parts. Simonov et al26 presented in 2007 a prototype of an adaptive IOL based on a modal liquid-crystal spatial phase modulator with wireless control.
The concept of refilling the emptied capsular bag with an elastic clear refracting material was presented in 200815 with devices that block anterior continuous curvilinear capsulorrhexis, possibly posterior continuous curvilinear capsulorrhexis, and prevent posterior capsule opacity. The device was tested to produce 2.0 D to 3.0 D of accommodation in monkey eyes in 2014.13
In 2008, a concept IOL with a rotating focus mechanism and a mechanical frame that can be operated by ciliary muscle contraction was designed and a prototype built.24 The proposed IOL was constructed of 2 optical elements that could rotate around an axis that is parallel to and decentered from the optical axis. Laboratory tests demonstrated 8.0 D of accommodation. No further development was published.
OPAL-A is a single-lens design introduced in 2010. The one-piece IOL is hydrophilic acrylic with a 5.5-mm diameter biconvex spherical optic and 4 flexible closed-loop haptics with an overall diameter of 9.8 mm, intended for implantation into the capsular bag. The IOL optic is designed to shift forward on the flexible haptics with accommodative effort.9 The OPAL-A was implanted in 22 eyes.9,68 Following 6 months, DCNVA was 0.34 ± 0.16, objective amplitude of accommodation was 0.1 D ± 0.34 D, subjective amplitude of accommodation was 2.5 D ± 0.62 D with push-up test and 0.93 D ± 0.35 D with defocus curves. The mean pilocarpine-stimulated forward IOL shift was 0.306 ± 0.161 mm by anterior segment OCT (Visante-1000) and 0.270 ± 0.155 mm by partial coherence interferometry (ACMaster; Carl Zeiss Meditec).
The FluidVision IOL is composed of a hollow fluid-filled hydrophobic acrylic optic and oversized hollow fluid-filled haptics. The fluid in the optic and haptics is an index-matched silicone oil that flows back and forth between the haptics and optic to change the curvature, and hence the power of the optic. FluidVision IOLs were examined upon rabbits since 2013.19,20 They induced less posterior capsular haze than a hydrophobic acrylic control IOL.
In 2015, McCafferty and Schwiegerling21 reported on a lens prototype that could achieve acceptable accommodation with forces available in the ciliary body, by deforming the interface between 2 materials with different refractive indices.
Trulign
In 2015, the Trulign toric IOL emerged. It is an astigmatism-correcting silicone multipiece IOL (model AT-50T or AT-52T) and is a toric modification of the parent Crystalens.8 The plate haptics are hinged adjacent to the optic and have small-looped polyimide haptics. The toric IOL is intended for placement in the capsular bag only. It has a spherical front (anterior) surface and a toric back (posterior) surface. Two marks on the peripheral anterior optical surface aid in proper alignment of the IOL, indicating the flat axis of the toric IOL. The available spherical equivalent powers range from +16.0 D to +27.0 D in 0.5-D increments with cylindrical powers at the lens plane of 1.25 D, 2.0 D, and 2.75 D (estimated cylinder power at the corneal plane 0.83 D, 1.33 D, and 1.83 D, respectively).
Recent Developments
A biomimetic accommodating IOL was proposed in 2016. The lens consists of a thin, deformable polymer shell with a self-sealing valve to allow an optically clear fluid to fill the lens. After filling, the lens takes the form of a natural crystalline lens, modeled after the natural 29-year-old human lens. The new clear and accommodating lens can function within the normal anatomy of the capsule, zonules, and ciliary body.14 This concept was tested in human cadaver eyes. As mentioned earlier, previously presbyopic human cadaver eyes were able to accommodate between 2.0 D to 7.4 D after lens implantation.14
Also in 2016, AkkoLens International BV developed a sliding-type IOL named the Lumina. It has 2 optical elements that slide in a plane perpendicular to the optical axis, producing a continuous variable-focus lens. The lens is positioned in the sulcus plane in front and on top of the capsular bag. The lens movement is driven directly by the ciliary muscle, without interference of the capsular bag. This allows the eye to focus continuously from far to near. When tested on cataract patients,23 it produced 1.27 D ± 0.76 D of objective accommodation at accommodation stimuli of 4.0 D, as compared to a 0.07 D ± 0.1 D for a monofocal control IOL. Uncorrected and corrected distance visual acuities and contrast sensitivity were similar over 12 months.
A new concept of voltage-controlled accommodating IOL made of an ionic polymer metal composite actuator was tested in vitro in 2016 to change focus.25 An actuator was placed inside the eye and moved with applied voltage. The lens attached to the actuator was deformed by its movement to change the lens power. The results showed that this system can accommodate a change of approximately 0.8 D under an applied voltage of ±1.3 V.
CONCLUSION
As the quest for presbyopic correction continues, accommodating IOLs seem to be the correct way to go. This is the only method that enables the retina to capture clear binocular images at varying distances, as all healthy subjects were accustomed to expect during childhood and early adulthood. Other methods require the use of spectacles (multifocal glasses), the use of one eye at a time with reduced depth perception (monovision), or reduced image quality (multifocal IOLs, pinhole apertures).
The complex requirements of an accommodative lens are the cause for the lack of success thus far. Most existing and past lenses are able to produce a good or very good image of a distance object with distance correction, but all fail to deliver the premium benefit of 3.0 D or more of objectively measured accommodation under accommodative stimulus.
Present designs of future lenses hold the promise to deliver a true accommodative response. That holy grail of surgical correction of presbyopia will by definition be an accommodating pseudophakos. However, these designs are described in a later chapter in this book.
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