Study On Mechanical Property Of Sclera And Whole Eyeball With Myopia Induced On Guinea Pigs

This paper presented a new method to measure the thickness of soft tissue, by which a device was constructed, and the thickness of sclera and cornea of rabbits and guinea pigs in varied location were measured. Three-dimensional finite element model of the sclera-cornea shell of rabbits and guinea pigs were constructed with data of its global dimension and sclera-cornea thickness. Furthermore, Standard linear viscoelastic model were used to simulate the creep data of uniaxial tension test. Nevertheless, the error in the fit curve and the test curve could not be neglected. As a result, a new constitutive equation for soft tissue was presented:ε=(A lnt + B)(lnσ + C), which was created on the basis of Fung's creep function: J(t) = Alnt + B. Our model is very easy to be used in fitting creep data, and its error is minor.The main part of this paper is to present a new method to measure the relation between internal pressure and volume change of eyes. The method was verified with an electric balance and applied on in vivo rabbit eyes and also on in vitro rabbit andguinea eyes. It was found that liquid exuded out from the tissue around the Optic Nerve Head (ONH) under high pressure, which would be well explained by stress concentration around the tissue of the ONH. As a matter of fact, this phenomenon agreed well with observation in glaucoma eyes, in which ONH was excavated under high pressure.At last, the mechanical property of guinea pig sclera, on which myopia was induced by -10D lens in 10, 30 and 45 days, were tested with our device and uniaxial tension device. With the data of myopia induced on guinea pigs, similar tendency could be found on both the test eyes and the control eyes, -4D relative myopia was induced in 10 days on the tested eyes, but retreat a little after 30 days and the relative myopia go further to -8D after 50 days, -3D relative myopia was found in the control eyes after 50 days. With the thickness data of sclera of guinea pigs, little change was found in the control eyes, whereas an increase at 30 days and a retreat at 50 days were both found. The data of the uniaxial tension test showed that with the increase of the induced days, the elastic strain increased on the test eyes, whereas creep strain of which decreased. And the creep strain unchanged on the control eyes, whereas electric strain of which increased in 30 days and then decreased in 50 days. With the results in the three test methods: in vivo, in vitro and uniaxial tension test, the strain in the vivo test was bigger than those in vitro test, whereas both of which were much less than those from uniaxial tension test.