Abstract
Abstract: :
Purpose: To describe the distribution of the lens stiffness within the human crystalline lens. Methods: Ten human lenses were obtained from donor eyes in the age range of 19–78 years old. The lenses were extracted from the eye and cut through the equatorial plane. The half lens section was placed in a lens–shaped fixture. In order to prevent the lens from drying during the measurement, the lens was covered with silicone oil and an aluminum plate. Local Dynamical Mechanical Analysis (DMA) was performed: a small piston (0.5–mm diameter) was put into the lens and the resistance to an oscillating movement of the piston was measured. Measurements were performed in the frequency range of 0.10–10 Hertz. The relationship between the measured force and the shear modulus of the material is defined by the shape factor. The shape factor was derived using a combination of analytical and numerical methods. Results:The measurements revealed a differerence in shear modulus between lens nucleus and cortex. For old lenses, the shear modulus in the lens center is higher than that in the periphery. For young lenses there is a maximum shear modulus close to the periphery. In the lens center, the shear modulus increases by a factor of 10.000 between the ages of 20 and 70, while in the periphery the shear modulus increases by a factor 100.The transition age at which the nucleus changes from being softer than the cortex to being stiffer than the cortex is around 40–50 years of age. Conclusions: In contrast to published data (Fisher, J Physiol, 1971), we found that the stiffness of the lens nucleus is significantly higher than the stiffness of the cortex for lenses over the age of 45 years, while for younger lenses, the stiffness of the nucleus is softer than the cortex.
Keywords: anatomy • aging