Light-Scattering Study of the Normal Human Eye Lens: Elastic Properties and Age Dependence

Abstract

The human ocular lens is a tissue capable of changing its shape to dynamically adjust the optical power of the eye, a function known as accommodation, which gradually declines with age. This capability is the response of the lens tissue to external forces which, in turn, is modulated by the biomechanical characteristics of lens tissues. In order to investigate the contributions of lens sclerosis to loss of accommodation, we report on in vitro confocal Brillouin light scattering studies of human ocular lenses spanning over a 30-70 year age range. Using this non-destructive measurement method, we determined that the longitudinal bulk modulus (average ± SD) of the lens nucleus (2.79±0.14 GPa) was consistently greater than the bulk modulus of the lens cortex (2.36±0.09 GPa). Moreover, our results showed that these differences were not age dependent over the 40 year age range that we evaluated using healthy lens tissues. Our results are consistent with the hypothesis that an age-dependent change in the bulk modulus of lens tissues does not fully account for the natural decline of accommodation.

Viscoelastic properties of fresh human lenses under 40 years of age: implications for the aetiology of presbyopia

“…The viscoelastic studies performed by Heys et al 10 and Weeber et al 11 found, contrary to the results of our study and those of others,3 8 18 that the cortices of lenses less than 40 years of age were stiffer than their nuclei. However, their measurements were made on lenses that had been frozen in liquid nitrogen at −70°C, rather than on fresh lenses.…”

“…Consistent with our findings, penetration studies using fresh human lenses,8 non-invasive techniques using ultrasound measurements of laser induced intra lens stromal bubble formation18 and Brillouin light scattering3 of intact human lenses have independently indicated that the stiffness of the cortex is less than or equal to the stiffness of the lens nucleus.…”

“…Neither the total water content of the lens cortex or nucleus,2 nor the bulk modulus3 nor the speed of ultrasound4 through the lens changes with age. The optical density of the lens nucleus5 and its pigmentation, surrogates for lens hardness, do not change significantly until after the age of 40 years 6.…”

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.…”

Assessing the mechanical properties of tissue-mimicking phantoms at different depths as an approach to measure biomechanical gradient of crystalline lens

“…Besides acoustic imaging techniques, Brillouin optical microscopy has recently been used to evaluate the elastic properties of the crystalline lens [11,12]. This method applies Brillouin spectroscopy to measure the frequency shift of the scattered light from the interaction between photons and acoustic phonons.…”