Scleral creep in vitro resulting from cyclic pressure pulses: applications to myopia

In the axially myopic eyeball, the posterior hemisphere is distended and the sclera is thinner in this region. One hypothetical mechanism is that high intraocular pressures cause an irreversible stretching of this region. For irreversible stretching to occur, the sclera must be stressed beyond the elastic limit. This paper presents a biaxial stress-strain curve for rabbit sclera and defines a plastic yield point. Experimental evidence is presented which demonstrates that cyclic pulses of high intraocular pressure can cause irreversible deformation. A mathematical equation is developed which successfully predicts creep rate (i.e., deformation rate) of an eye subjected to short duration pulses of high intraocular pressure. This relation holds for frequencies of cyclic pressures which vary over two orders of magnitude, and over a wide range of temperatures and pressures.