The elastic constants of the human lens

Abstract

SUMMARY1. When the lens is spun around its antero-posterior polar axis in an apparatus designed for the purpose, high speed photography can be used to record its changing profile. By this method a variable radial centrifugal force can be applied to the lens which mimics the pull of the zonule.2. If the lens is not stressed at its centre beyond 100 Nm-2 it behaves as a truly elastic body. When stressed beyond this limit visco-elastic strain is produced at its poles.3. The human lens has isotropic elastic properties at the extremes of life, but at the other times Young's Modulus of Elasticity varies with the direction in which it is measured.4. Young's Modulus of Elasticity of the lens varies with age, polar elasticity and equatorial elasticity, at birth being 0 75 x 103 and 0-85 x 103 Nm2 respectively, while at 63 years of age both are equal to 3 x 103 Nm2. 5. A comparison of Young's Modulus of the young human lens with that of the rabbit and cat shows that the polar elasticity of the lenses of these animals was 5 times greater in the young rabbit, and 21 times greater in the adult cat. Equatorial elasticities of the rabbit and human lens were equal, while in the cat the equatorial elasticity was four times greater.6. A mathematical model showing the lens substance possessing a nucleus of lower isotropic elasticity than that of the isotropic elastic cortex surrounding it, accounts for the difference between polar and equatorial elasticity of the intact adult lens.7. The implications of these findings are discussed in relation to: (i) accommodation and the theological properties of the lens; (ii) possible differences in the physical state of the lenticular proteins in the cortex and nucleus which may account for the senile variations in Young's Modulus of Elasticity in these regions of the lens;(iii) the loss of accommodation due solely to an increase in Young's Modulus of Elasticity of the lens between the ages of 15 and 60. This would amount to 44 % of the total observed in vivo.

Simulating the Mechanics of Lens Accommodation via a Manual Lens Stretcher

“…These results demonstrated a smaller difference between stretched and unstretched radius of the 60 year-old lens compared to the 21-year-old lens, indicating a loss of accommodation ability. The older human lens demonstrating a decreased ability to stretch is in agreement with similar studies on accommodation as a function of age 8,18,20 .…”

Simulating the Mechanics of Lens Accommodation via a Manual Lens Stretcher

“…These results demonstrated a smaller difference between stretched and unstretched radius of the 60 year-old lens compared to the 21-year-old lens, indicating a loss of accommodation ability. The older human lens demonstrating a decreased ability to stretch is in agreement with similar studies on accommodation as a function of age 8,18,20 .…”

Storage-induced mechanical changes of porcine lenses assessed with optical coherence elastography and inverse finite element modeling

“…Further increasing the freezing rate to −190 °C by immersing the eye globe into liquid nitrogen did burst the eye and thus was not feasible, at least for intact eye globe preservation. The current study is in agreement with earlier findings that suggest storage in the refrigerator (Fisher, 1971) does not significantly affect the lens mechanics.…”

Gradient moduli lens models: how material properties and application of forces can affect deformation and distributions of stress

“…The cortex in the smallest of these lens models, based on the 16-year-old lens 20 , is divided into four layers; the cortical regions in the other two lenses have five layers. Young’s moduli for each model increases by 0.6 MPa increment from the innermost to the outermost layer, maintain a mean value of all layers that is in accordance with the values reported by Fisher 8 ; Young’s moduli of the nucleus is constant. Layered stress patterns are observed in the anterior and posterior cortical regions of the 16-year-old lens, and largely in the posterior cortical region for the 35-year-old and the 48-year-old lenses.…”

“…Models with multiple cortical layers with gradient elastic moduli were created based on the contours of refractive index of each particular lens 20 . The moduli in the cortex of these multi-layer models increased from the innermost to the outermost layers, maintain a mean value of all the cortical layers in accordance with previous measurements 8 12 .…”

Simulating the Mechanics of Lens Accommodation via a Manual Lens Stretcher

“…These results demonstrated a smaller difference between stretched and unstretched radius of the 60 year-old lens compared to the 21-year-old lens, indicating a loss of accommodation ability. The older human lens demonstrating a decreased ability to stretch is in agreement with similar studies on accommodation as a function of age 8,18,20 .…”

Storage-induced mechanical changes of porcine lenses assessed with optical coherence elastography and inverse finite element modeling

“…Further increasing the freezing rate to −190 °C by immersing the eye globe into liquid nitrogen did burst the eye and thus was not feasible, at least for intact eye globe preservation. The current study is in agreement with earlier findings that suggest storage in the refrigerator (Fisher, 1971) does not significantly affect the lens mechanics.…”

Gradient moduli lens models: how material properties and application of forces can affect deformation and distributions of stress

“…The cortex in the smallest of these lens models, based on the 16-year-old lens 20 , is divided into four layers; the cortical regions in the other two lenses have five layers. Young’s moduli for each model increases by 0.6 MPa increment from the innermost to the outermost layer, maintain a mean value of all layers that is in accordance with the values reported by Fisher 8 ; Young’s moduli of the nucleus is constant. Layered stress patterns are observed in the anterior and posterior cortical regions of the 16-year-old lens, and largely in the posterior cortical region for the 35-year-old and the 48-year-old lenses.…”

“…Models with multiple cortical layers with gradient elastic moduli were created based on the contours of refractive index of each particular lens 20 . The moduli in the cortex of these multi-layer models increased from the innermost to the outermost layers, maintain a mean value of all the cortical layers in accordance with previous measurements 8 12 .…”

Simulating the Mechanics of Lens Accommodation via a Manual Lens Stretcher

“…These results demonstrated a smaller difference between stretched and unstretched radius of the 60 year-old lens compared to the 21-year-old lens, indicating a loss of accommodation ability. The older human lens demonstrating a decreased ability to stretch is in agreement with similar studies on accommodation as a function of age 8,18,20 .…”

Storage-induced mechanical changes of porcine lenses assessed with optical coherence elastography and inverse finite element modeling

“…Further increasing the freezing rate to −190 °C by immersing the eye globe into liquid nitrogen did burst the eye and thus was not feasible, at least for intact eye globe preservation. The current study is in agreement with earlier findings that suggest storage in the refrigerator (Fisher, 1971) does not significantly affect the lens mechanics.…”

Gradient moduli lens models: how material properties and application of forces can affect deformation and distributions of stress

“…The cortex in the smallest of these lens models, based on the 16-year-old lens 20 , is divided into four layers; the cortical regions in the other two lenses have five layers. Young’s moduli for each model increases by 0.6 MPa increment from the innermost to the outermost layer, maintain a mean value of all layers that is in accordance with the values reported by Fisher 8 ; Young’s moduli of the nucleus is constant. Layered stress patterns are observed in the anterior and posterior cortical regions of the 16-year-old lens, and largely in the posterior cortical region for the 35-year-old and the 48-year-old lenses.…”

“…Models with multiple cortical layers with gradient elastic moduli were created based on the contours of refractive index of each particular lens 20 . The moduli in the cortex of these multi-layer models increased from the innermost to the outermost layers, maintain a mean value of all the cortical layers in accordance with previous measurements 8 12 .…”