INNOVATIVE INTRAOCULAR LENS DESIGN
PROVEN WITH SIMULATION.
Simulation Halves Mechanical Design Cycle Time
And Leads to 80% Reduction in Manufacturing
Time and Cost.
Simulation Halves Mechanical Design
Cycle Time and Leads to 80% Reduction
in Manufacturing Time and Cost.
An ophthalmologist desiring to provide patients with a wider
range of vision utilizing a more natural solution, Mona F.
Sarfarazi, M.D, FICS, has developed the Sarfarazi
Innovative Elliptical Accommodative Intraocular Lens
(EAIOL), a concept enabling the brain and eye muscles to
focus for close up and distance vision. With the use of
simulation provided by MSC.Software Professional
services, the principle behind the Sarfarazi EAIOL concept
was proven before prototypes were made. Additionally,
simulation enabled optimization of the EAIOL concept,
providing a 50% reduction in time-to-market and leading to
an 80% reduction in manufacturing costs. Currently the
Sarfarazi EAIOL is expected to go under FDA testing later
this year and is expected to be on the market within the
next two to three years, when it will deliver a substantial
improvement in the quality of life for millions of patients.
HOW THE SARFARAZI EAIOL SYSTEM
WORKS
The Sarfarazi EAIOL system is made of two components,
the haptics and the optics. The haptics are a curved
membrane that controls the distance between two lenses,
enabling a change in focal distance. The Sarfarazi EAIOL
system utilizes the contraction/relaxation of the muscles
surrounding the equator of the natural lens for focusing.
Natural focusing occurs when the fibers attaching the
muscles around the natural lens pull on the lens, changing
its shape, and in turn changing the focal distance. Sarfarazi
EAIOL focusing occurs by utilizing the ciliary muscles to pull
and release the haptics, varying the distance between the
two lenses.
“The lens is folded up and inserted through a 2-3 mm
incision, which is too small to be seen by the eye,”
explained Dr. Sarfarazi. “The surgery time is only 15-20
minutes. If the patient is not happy with it, you take it out.
There is no damage to the eye and another lens can be
inserted. This lens works with the muscle in the eye and the
brain, providing a long range of vision. Current techniques
for surgically improving vision include various types of laser
surgery and replacement of the natural lens. Laser surgery
permanently changes the surface of the cornea and it is
irreversible. Lens replacement limits the vision range
because it only provides a fixed focus and often requires
glasses for reading and close up work. Laser Surgery is
limited to adults, which limits the quality of life during early
years.
BENEFICIARIES OF THE SARFARAZI EAIOL:
Patients that can benefit from the Sarfarazi EAIOL span all
ages from infant to senior citizens and fall into one of five
groups, including:
v Cataract Patients: Every year 2.8 million cataract
surgeries with intraocular lens implantation are
performed in the USA and 3.2 million in other countries
around the word.
v Presbyopia: an estimated 50 million people over 40
years of age live in USA alone. The el ns could
eliminate the use of reading and bifocal glasses for
near and distance vision for this group.
v Myopia: The lens is an alternative to laser surgery and
implanted contact lenses (ICL). As a permanent
solution, the Sarfarazi EAIOL, not only could provide
distance vision, but also could preserve the
accommodation in high myopic patients.
v Congenital Cataract: This lens could be implanted in
an infant’s eye with congenital cataract after cataract
extraction. A full range of accommodation and a clear
vision for near and distance could achieved throughout
their life.
v Macula Degeneration: The Sarfarazi EAIOL could
provide high magnification and a clear and wide field of
vision for patients with this disorder.
SIMULATION
The objective in utilizing simulation was to determine an
acceptable size, shape and material for a range of focal
lengths, which is both manufacturable and can be folded
(nested) for surgical implantation.
MSC.Software’s
Professional Services utilized MSC.Nastran and
MSC.Patran finite element analysis (FEA) simulation
software to simulate the Sarfarazi EAIOL system. The 2D
and 3D EAIOL geometry was created using MSC.Patran,
while boundaries, restraints and loads were modeled in
MSC.Nastran, which was also utilized for running the
analysis and post processing results.
“When MSC.Software Professional Services started
working with me, we made changes that optimized the
design,” said Dr. Sarfarazi. “Now we have three parts
called haptics, which is like a membrane, and two optics or
lenses. We started with five haptics and along the way; we
tested three and six haptics to find the most stable
combination. Stimulation of this system inside the bag had
proven that the lens system with three haptics has the best
possible design mechanically.
Initial analyses were conducted using a 2D axisymmetric
approach, enabling 3D geometry to be evaluated using a
2D model. A 2D model has fewer elements than a 3D
model of the same component requiring less processing
time. However, there was a requirement for a constant
cross-section revolved about an axis (solid of revolution).
While this proved to be adequate for a large number of
initial analyses, ultimately a 3D model was developed as
the design evolved into a shape that was not a solid of
revolution. As the final configuration consisted of three
similar 120° segments, each with a similar loading, only a
single segment had to be analyzed. This characteristic is
referred to as cyclic symmetry, which significantly reduced
the model size and corresponding run times. The capsular
bag was not included in the model, because initial runs
using the 2D model revealed that the low stiffness of the
capsular bag had a negligible effect on the system’s
response.
FOCUSING WITH THE SARFARAZI EAIOL
SYSTEM
The design and function of the SARFARAZI EAIOL dictated
the basic shape of the lens, two lenses connected by a
membrane. Intuition and initial studies indicated the lens
shape would not have a significant impact on the motion of
the Sarfarazi EAIOL assembly, as compared to the haptics,
the lens is much stiffer and moves as a rigid component.
The challenge was to determine a design delivering the
necessary motion of the lenses with available materials.
The focusing or accommodation process occurs in the
human eye by a reshaping of the lens, occurring when the
eye muscles relax and the fibers connecting the muscles to
the lens, the Zonula of Zinn, pull outwardly on the lens. The
accommodative intraocular lens achieves the same result
by a slightly different technique. Accommodation in the
Sarfarazi EAIOL is achieved by the pull on the connecting
membrane between the lenses from the Zonula of Zinn
moving the lenses closer together.
Measurements indicated that the Zonula pull outwardly on
the human lens and the value was applied to the finite
element model as a prescribed displacement. Because
qualitative data was not available about how this motion
varied, if at all, around the periphery of the lens, the motion
was assumed to be uniform around the entire
circumference. In addition, it was assumed that pressure
from the vitreous would prevent the posterior lens from
moving backward, maintaining the distance from the
posterior lens to the retina.
Optics analysis indicated that an acceptable range of focal
lengths could be achieved with approximately 2.0 mm of
relative motion of the lenses. Given the specified boundary
conditions, the geometry and material could be varied to
achieve the desired objective. The geometry variation is
somewhat limited, as the lens assembly must fit into the
bag of the natural lens. The elliptical shape of the final
cross-section mimics the shape of the human capsular bag
where it will be inserted. Also of interest during the initial
analyses was the fact that if the cavity in between the two
lenses was filled with a trapped fluid, the effective stiffness
of the lens assembly was increased significantly. This
stiffness increase was detrimental to the performance of the
lens so a vented design was applied, enabling internal fluid
to migrate into and out of the cavity in the chamber in front
of the anterior lens. Although stiffness was significantly
reduced, results of the analyses indicated a level of
accommodation much less than the desired 2.0 mm.
To reduce the stiffness and increase the accommodation,
an interrupted solid of revolution where the haptics
occupied only three 40° segments was simulated. This
design resulted in an accommodation of 1.9 mm. The nonlinear nature of this response curve is characteristic of this
type of system allowing a larger motion in the relative lens
movement than in the Zonula.
MATERIAL EVALUATION
Numerous materials were evaluated for the purpose of this
study. In general, softer materials were much more
desirable because they provided a higher level of
accommodation. However, the interrupted solid of
revolution design allowed the use of PMMA, a relatively stiff
material but well tested and proven for optics use.
Additional analyses was run on the assembly, including
stress, stress intensity, and tensile stress.
SIMULATION ENHANCES DESIGN
MANUFACTURING PROCESSES
AND
“Simulation helped us refine the design concept, decide on
the best material and prove that the concept works,” said
Dr. Sarfarazi. “Because of design changes made as a
result of simulation, manufacturing is made much easier.
By making the lens with a mold, eliminating manual
intervention, the EAIOL comes out of the mold finished as a
complete unit. The simulation provided by MSC.Software
Professional Services has impacted our design, testing and
manufacturing, as well as reduced costs and time-tomarket.”
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