Abstract
Purpose :
There have been many studies on the mechanism of accommodation, identifying the ciliary muscle as the prime source of crystalline lens shape changes. This process may be affected by the Wieger ligament, a stiff, annular structure attached to the posterior lens capsule. This work investigates how this ligament affects the shape of the lens at rest.
Methods :
A 2D axisymmetric model of the entire eye was developed in ANSYS (Ansys Inc, Southpointe, PA, USA), including the cornea, limbus, sclera, iris, zonular fibers, ciliary muscles, crystalline lens, lens capsule and the Wieger ligament (Figure 1). Next, the finite element method was used to simulate accommodation, considering isotropic elastic materials for the lens, capsule, iris, zonules, and ciliary body, and hyperelastic material for the cornea, limbus, and sclera. Zonular fibers were modeled as five sets of beam elements. The initial state of the model was maximal accommodation, when according to Helmholtz' theory the zonular fibers are relaxed, and the ciliary muscle is contracted. Relaxation of the ciliary muscle was simulated as a gradual displacement away from the equatorial axis. This way, four states were considered to observe the influence of the Wieger ligament: without ligament, and ligaments with a stiffness that is the same, twice and three times that of the lens capsule. The lens’ radii of curvature were extracted for each simulation to calculate the optical power using the thick lens equation, assuming an equivalent lens refractive index of 1.43.
Results :
Including the Wieger ligament with the same stiffness as the lens capsule leads to a 0.34D decrease in the total power of the non-accommodated lens (Figure 2). The ligament affected both surfaces differently, with a decrease in the posterior power (-0.63D) and an increase in the anterior power (+0.29D). Both effects increase for higher ligament stiffness values. The position of the anterior lens apex shifts forward by 0.04 mm for a ligament with the same stiffness as the capsule, while the posterior surface shifts backward by 0.06 mm.
Conclusions :
The Wieger ligament has a noticeable effect on the entire lens geometry of the lens focused for distance vision that may need to be considered when modelling accommodation.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.