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Updated: May 21, 2025
05:14
Simulating the Mechanics of Lens Accommodation via a Manual Lens Stretcher
Published on: February 23, 2018
6.7K
Finite element analysis of the lens profile during accommodation
Ronald A Schachar1, Ira H Schachar2, Xiaomeng Li3
1Department of Physics, University of Texas at Arlington, Arlington, Texas, United States of America.
Plos One
|March 17, 2025
Summary
Understanding human lens accommodation requires knowing zonular forces. Minimal equatorial zonular force increase drives significant power change, independent of nuclear stiffness, suggesting it
Area of Science:
- Ophthalmology
- Biomechanical Engineering
- Vision Science
Background:
- Human lens accommodation, crucial for near focusing, involves ciliary muscle contraction and significant changes in lens optical power.
- The precise role and magnitude of zonular forces in altering human lens shape during accommodation remain under investigation.
- Age-related presbyopia is linked to a decline in accommodative amplitude, but its exact etiology is not fully understood.
Purpose of the Study:
- To evaluate the correlation between zonular forces and human lens shape changes, including curvatures, thickness, and optical power.
- To investigate the influence of varying lens nuclear elastic moduli on the forces required for accommodation.
- To determine if nuclear stiffening is the cause of age-related presbyopia.
Main Methods:
- Finite element (FE) analysis was employed to model the human lens.
- Analyses were based on fresh human lenses from donors aged 20-30 years.
- Simulations involved stepwise increases in equatorial zonular (Ez) force and decreases in anterior (Az) and posterior zonular (Pz) forces, with varied nuclear-to-cortex elastic modulus ratios.
Main Results:
- A minimal Ez force increase (<0.02 N) was sufficient to achieve a 10-diopter increase in central optical power (COP), with concurrent Az and Pz force decreases.
- Lens shape changes included peripheral flattening, central steepening, increased central thickness, and a shift in longitudinal spherical aberration (LSA) towards negative values.
- The accommodative response was independent of the lens nuclear elastic modulus, even when significantly increased.
Conclusions:
- Increasing Ez force while decreasing Az and Pz forces is the primary mechanism for lens shape change during accommodation.
- The study refutes nuclear stiffening as the cause of age-related presbyopia.
- Findings have implications for understanding and treating myopia, glaucoma, presbyopia, cataracts, and designing accommodative intraocular lenses.
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