Stiffness gradient in the crystalline lens

Abstract

Background While the overall stiffness of the lens has been measured in a number of studies, the knowledge about the stiffness distribution within the lens is still limited. The purpose of this study was to determine the stiffness gradient in the human crystalline lens. A secondary purpose was to determine whether the stiffness gradient depends on age. Methods The local dynamic stiffness was measured in 10 human crystalline lenses (age range: 19 to 78 years). The lenses were stored at −70°C before being measured. The influence of freezing on the mechanical properties has been determined in a previous study. A small oscillating probe was used to measure the local dynamic shear modulus as a measure of lens stiffness. The measurements were taken in the cross-sectional plane through the lens equator. Results The local dynamic shear modulus varied with location for all tested lenses. The central stiffness of the oldest lens (78 years) was 10 4 times higher than the youngest (19 years) lens. The equatorial stiffness of the oldest lens was 10 2 times higher than the youngest lens. For the older lenses, the centre was 5.8-210 times stiffer than the periphery, as opposed to earlier results described by Fisher (1971), who found that the periphery was up to 3 times softer than the centre for lenses younger than 70-years-old. For the three youngest lenses (19 to 49 years), the periphery was 2.2-16.6 times stiffer than the centre. Conclusions The dynamic stiffness of the crystalline lens varies with location within the lens. The stiffness gradient depends on the age of the lens. The results of the 10 lenses indicate that the stiffness of both centre and periphery increase with age, but at a different rate.

Objective accommodation measurements in prepresbyopic eyes using an autorefractor and an aberrometer

“…[4][5][6][7][8] Although there are changes to most of the anatomical structures involved with accommodation with age (eg, altered ciliary body configuration, loss of capsule elasticity), the most significant change with age is increased stiffness of the lens. 3,5,[9][10][11][12] There has been considerable interest in prospects for surgically restoring active and dynamic accommodation to the presbyopic eye with scleral expansion procedures or intraocular lenses (IOLs) designed to move with an accommodative effort to create a true change in the optical power of the eye for objects at near distances. [13][14][15][16][17][18][19][20][21][22][23][24][25] Although subjective clinical assessments suggest high levels of patient satisfaction and good visual performance, 14,[24][25][26] objectively measured accommodative performance with these procedures have been disappointing.…”

Pathophysiology of cataracts

“…On the other hand, young adults are found to have an elastic deformable lens. 17 Elasticity and stiffness will become equal in both nucleus and cortex around the age of 40 years. Then, the nucleus will gradually become more rigid and stiff than the cortex.…”

Inverse elastographic method for analyzing the ocular lens compression test

“…6 Previous methods for estimating lens sti®ness include spinning tests, [7][8][9] dynamic mechanical analysis, 10 indentation, 11,12 penetration, 13 Brillouin microscopy, [14][15][16][17][18][19] acoustic methods, 20,21 and compression. [22][23][24][25][26][27] The lens capsule has been mechanically characterized by in°ation testing 28,29 and uniaxial tensile testing.…”