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 lens 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 non-linear 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 AND MANUFACTURING PROCESSES

“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-to-market.”

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