Effects of ocular dimensions on IOP-related stress within the optic nerve head and posterior scleral shell

In glaucoma, retinal axons are damaged as they pass through the connective tissue beams (the lamina cribrosa) which span the scleral canal. We created a set of idealized finite element models (FEMs) of the posterior scleral shell of the human eye to study stresses within the lamina cribrosa and surrounding sclera. These models incorporate a range of human dimensions for scleral wall thickness (SWT), axial length (AL), and size and shape of the scleral canal. Stresses within the laminar tissues of circular canals ranged from 48/spl times/IOP (intraocular pressure) to 163/spl times/ IOP. In regions where laminar tissues inserted into the surrounding scleral shell, stresses were highest on the anterior (inner) side of the laminar beams. For elliptically shaped canals, the ratio of vertical to horizontal diameters had an effect on the maximum laminar stress and maximum stress at the insertion zones, and on the distance from the canal where the sclera withstands increased stresses. Decreasing SWT led to significant increases in laminar, insertion zone, and peripapillary scleral stress. Changes in AL of the hemisphere had little effect on stresses within the tissues.