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MV Subbaram, JC Gump, MA Bullimore, R Sooryakumar; The Elasticity of the Human Lens . Invest. Ophthalmol. Vis. Sci. 2002;43(13):468.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Presbyopia has been attributed to changes in the visco-elastic properties of the lens but there is no clear consensus on how the physical properties change with age. In an attempt to further understand these properties, we have measured the longitudinal elastic constant (C1,1), using a non-invasive technique (Brillouin light scattering). Methods: A total of 19 fresh human donor lenses were obtained from the Ohio Lions Eye bank. The age of the donors ranged from 30 to 64 years. The lenses were stored in a freshly prepared, balanced salt solution (pH = 7.4) with an osmolarity similar to that of the vitreous. The weight and volume of the lenses were measured to calculate the density. Brillouin light scattering is an established technique for measuring the longitudinal elasticity constant of an organic or inorganic sample. A few milliwatts of 514.5 nm laser radiation from an argon-ion laser were focussed to a 50µm spot on the human lens using a +20 D objective. The incident radiation was focussed at various locations within the lens and the resulting shift in frequency of the back-scattered radiation was measured. The scattered light is dispersed by a Fabry-Perot interferometer and detected by a solid state photon detector. The intensity of the inelastically scattered beam is plotted as a function of frequency shift for a range of longitudinal positions throughout the human lens. C1,1 is then calculated using the formula, C1,1 = ρ λ2f2/4n2, where ρ is the density of the lens, λ is the wavelength, f is the frequency shift, and n is the refractive index of the lens Results: The average C1,1 value was 3.67 ± 0.71 GPa and 2.80 ± 0.58 GPa for the nucleus and the cortex, respectively. There was a significant difference in the mean C1,1 values between the nucleus and the cortex (t = 17.07, p < 0.001). Conclusion: Brillouin light scattering is a useful technique that enables measurement of the elasticity of different portions of the lens.
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