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TECHNOLOGY WATCH
Section Editor: John A. Vukich, MD
New Accommodating IOLs
Variable-focus accommodating IOL designs dominate the next wave of lens research.
BY JOHN A. VUKICH, MD, SECTION EDITOR
Welcome to the inaugural issue of Advanced Ocular Care!
“Technology Watch” will be a regular column highlighting the
innovations in ophthalmic surgery that shape the treatment
of patients. The 5-year horizon for new techniques, technology, and equipment in this medical field is often visible in the
results of early clinical trials and international experience.
This column will feature experts from around the world who
will share their insights into the latest developments. Some of
the featured technologies may be available now; others may
be several years from the market. Collectively, however, these
innovations are the leading indicators of where ocular care is
headed. In AOC’s coming issues, this column will cover laserassisted cataract extraction, glaucoma devices, and real-time
aberrometry as well as other new technologies. I hope you
find “Technology Watch” to be a valuable source of information on the innovations shaping the future of eye care.
F
ueled partly by the aging of the population and
partly by advances in technology, research in
accommodating lenses is leading the field of presbyopic correction. A number of accommodating IOLs
are currently in use or under investigation. They fall into two
general categories: (1) those with a mechanism that depends on forward movement of a single or dual optic and
(2) those with a mechanism that depends on a change in
the curvature of the lens’ surface. In addition, other factors
are known to influence a patient’s near vision, and their
effect is collectively referred to as pseudoaccommodation.
Increased depth of field affected by pupillary size, low residual against-the-rule astigmatism, and higher-order aberrations (in particular, spherical aberration and coma) all can
play a part in the IOL’s mechanism of action and influence
the net effect of the restoration of functional near vision.1
THE MECHANISM OF NATURAL
ACCOMMODATION
An emmetropic eye is focused for distance when the
ciliary muscle is relaxed. Resting tension on the zonular
fibers extending between the ciliary body and the lens
capsule pulls the natural lens into a flat, unaccommodated state. Contraction of the ciliary muscle occurs with
near-focusing effort. When the ciliary muscle contracts,
the ciliary body moves inward, releasing resting zonular
tension. When the zonular tension relaxes, the elastic
capsule surrounding the lens of a young eye molds the
soft, deformable cortex and nucleus into a more spherical and accommodative form. This change decreases the
lens’ diameter, increases its axial thickness, and, most
importantly for the accommodative effect, steepens the
curvature of the lens’ anterior and posterior surfaces.2-5
IOL S THAT MOVE IN THE Z AXIS
Common to all accommodating IOL designs is the
assumption that mechanical force generated by the ciliary
body, vitreous pressure, or movement within the eye can
be used to change the refractive power of the IOL. In the
case of both single- and dual-optic designs, a change in the
effective lens position is used to achieve an accommodative
effect. Anterior movement of a plus-powered IOL changes
the effective lens position, which results in a net gain in
power. The higher the positive lens power is, the more net
effect there will be for a given amount of movement. This is
the theoretical basis for the mechanism of action for the
single- as well as dual-optic accommodating IOLs.1
The only accommodating IOLs approved by the FDA are
the Crystalens Five-O, Crystalens HD, and Crystalens AO
(Bausch + Lomb, Rochester, NY). Other single-optic lenses
with a potential accommodative effect include the Tetraflex
(Lenstec, Inc., St. Petersburg, FL) and the Akkomodative 1CU
(HumanOptics AG, Erlangen, Germany). Although all of
these IOLs have been reported to have some beneficial near
effect, their mechanism of action cannot be fully explained
by a change in axial position.6-8 Clinical studies using a variety
of measurement techniques have shown that lens movement is unreliable, small in amplitude (0.5 mm or less), and
in some cases, opposite in direction.9 In order to explain the
observed improvement in near vision experienced by some
patients, alternate theories of action have been proposed,
including optic deformation with increased spherical aberrations.1 Although their mechanism of action may not be fully
understood, the initial commercial success of single-optic
accommodating IOLs has generated substantial interest in
the development of improved designs (Figures 1 to 3).
The Synchrony dual-optic accommodating IOL (Abbott
Medical Optics Inc., Santa Ana, CA) represents a novel
design, which is intended to enhance the optical effect of
the lens’ movement. The IOL has a 5.5-mm, 32.00 D front
optic connected by spring haptics to a 6.0-mm posterior
JANUARY/FEBRUARY 2010 ADVANCED OCULAR CARE 19
TECHNOLOGY WATCH
Figure 2. The Tetraflex is designed to vault anteriorly in disaccommodation. In theory, dynamic forces within the eye during accommodation cause the optic to move anteriorly and
increase net effective power.
Figure 1. The Crystalens AT-45 was the first accommodating
IOL to become available in the United States. The Crystalens
Five-O (shown here) is designed to vault posteriorly in disaccommodation. In theory, greater vitreous pressure during
accommodation causes the optic to move anteriorly and
increase net effective power.
optic of variable negative power. The single-piece silicone
lens comes preloaded in an injector system and is inserted
through a 3.6-mm incision. During resting disaccommodation, tension on the capsular bag compresses the optics
together, storing energy in the connecting haptics. When
the ciliary muscle contracts during accommodation, the
zonules relax and release tension on the capsular bag. This
change allows the spring-like energy of the compressed
IOL to cause forward movement of the front optic.
Thin lens optical calculations predict that 1.5 mm of
movement by a 32.00 D anterior optic will result in 3.50 D of
accommodation. An important feature of the Synchrony
IOL’s design is that only the anterior 32.00 D lens moves, and
because this is a fixed power, the amplitude of accommodation will be consistent across all lens sizes and will not vary
among individuals. A study by Ossma et al reported a difference in mean accommodative range between eyes implanted with the Synchrony lens and control eyes that
received a monofocal acrylic IOL (ie, Synchrony 3.22 ±0.88 D
[range, 1.00-5.00 D] vs monofocal 1.65 ±0.58 D [range, 1.002.50 D]).10
The Synchrony lens has a three-dimensional structure,
which fills the capsular bag and, when expanded, approximates the shape of the natural crystalline lens. It has been
postulated that preserving the physiologic angle of attachment of the zonules to the capsular bag facilitates the translation of energy from ciliary movement.11 The expanded dualoptic IOL fully occupies the capsular bag, which may play a
role in the low levels of posterior capsular opacification that
have been observed.11 The lens received the CE Mark and has
20 ADVANCED OCULAR CARE JANUARY/FEBRUARY 2010
Figure 3. The Akkommodative 1CU is designed to have fourpoint fixation within the capsular bag. Its haptics are
designed to facilitate anterior movement of the lens.
been available commercially in Europe since January 2009. It is
currently under review by the FDA (Figure 4).
IOL S THAT CHANGE THE CURVATURE
OF THE OPTIC
Several lenses in the early stages of development are
designed to change the optic’s radius of curvature upon
accommodative effort. The NuLens (NuLens Ltd. Herzliya
Pituah, Israel) is a sulcus-fixated accommodating IOL. This
lens is designed to be implanted in front of the anterior and
posterior lens capsules, which serve as a diaphragm that
moves with accommodative effort. The transfer of force
from the capsular diaphragm to the optic is accomplished
via a piston element that is a part of the lens.12 In theory, the
design specifications of the NuLens’ deformable optic could
produce up to 10.00 D of accommodation.13 The NuLens
has undergone preliminary human trials in Mexico. Currently, the IOL needs a large incision for implantation, but
newer designs may reduce this requirement (Figure 5).
TECHNOLOGY WATCH
Figure 4. The Synchrony dual-optic IOL features a highpowered anterior optic and a negatively powered posterior
optic that are separated by spring-like haptics.
Figure 5. The sulcus-fixated NuLens is designed to rest on the
collapsed anterior and posterior capsules. A piston mechanism drives fluid, which alters the radius of a deformable
anterior membrane.
properties of a young human eye. The current generation
of single-optic IOLs will soon be joined by a dual-optic
design that may provide more consistent results and thus
broaden the use of accommodating lenses. Early prototypes of lenses with an even greater potential for accommodation are in various stages of development.
One thing is certain: If investigators are able to develop
an IOL that reliably provides 5.00 D of peak and 2.50 D of
sustained accommodation, it will forever change the face
of cataract and refractive surgery. ■
Figure 6. The FluidVision Lens uses a reservoir of liquid in its
haptics to hydraulically alter the shape of the central optic.
The FluidVision Lens (PowerVision Inc., Belmont, CA)
moves fluid through channels from its soft haptics to a
fluid-driven internal deformable membrane. This hydraulic
action produces a controlled increase in the anterior curvature of the deformable optic’s anterior surface. Preliminary
studies14 conducted in blind eyes have demonstrated an
accommodative change of up to 8.00 D (Figure 6).
Another shape-changing lens under development is
HumanOptics’ Superior Accommodating IOL. This lens
has a soft, gel-like internal nucleus surrounded by an elastic membrane designed to mimic the behavior of the
youthful natural crystalline lens.
CONCLUSION
The correction of near vision can be improved by a variety of mechanisms that couple the mechanical forces of
natural accommodation with an IOL designed to variably
change its net optical power. The majority of research in
new lens designs centers on developing an IOL that provides a smooth variable focus, thus mimicking the optical
22 ADVANCED OCULAR CARE JANUARY/FEBRUARY 2010
Section Editor John A. Vukich, MD, is a partner at Davis Duehr Dean Center for Refractive
Surgery in Madison, Wisconsin. He has served as
a consultant to Abbott Medical Optics Inc. as
well as to other companies not mentioned herein with interests in accommodation, presbyopia, and
accommodation-restoration concepts. Dr. Vukich may be
reached at (608) 282-2000; [email protected].
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2. Glasser A,Campbell MCW.Biometric,optical and physical changes in the isolated human crystalline lens with age
in relation to presbyopia.Vision Res.1999;39:1991-2015.
3. Weeber HA,Eckert G,Soergel F,et al.Dynamic mechanical properties of human lenses.Exp Eye Res.2005;80:425-434.
4. Glasser A,Kaufman PL.The mechanism of accommodation in primates.Ophthalmology.1999;106:863-872.
5. Rosales P,Wendt M,Marcos S,Glasser A.Changes in crystalline lens radii of curvature and lens tilt and decentration
during dynamic accommodation in rhesus monkeys.J Vis.2008;8:18-22.
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lenses:a randomized trial [published online ahead of print November 26,2007].Ophthalmology.2008;115(8):993-1001.
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intraocular lenses.J Cataract Refract Surg.2009;35(10):1711-1714.
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[published online ahead of print March 21,2007].Ophthalmology.2007;114(9):1679-1684.
9. Findl O,Leydolt C.Meta-analysis of accommodating intraocular lenses.J Cataract Refract Surg.2007;33:532-537.
10. Ossma IL,Galvis A,Vargas LG,et al.Synchrony dual-optic accommodating intraocular lens.Part 2:pilot clinical
evaluation.J Cataract Refract Surg.2007;33:47-52.
11. McLeod SD,Vargas LG,Portney V,Ting A.Synchrony dual-optic accommodating intraocular lens.Part I:optical and
biomechanical principles and design considerations.J Cataract Refract Surg.2007;33:37-46.
12. Ben-Nun J.The NuLens accommodating intraocular lens.Ophthalmol Clinic North Am.2006;19:129-134.
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and Science.Thorofare,NJ:Slack,Inc.;2008:223-228.
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