DEFORMATION OF THE LAMINA-CRIBROSA BY ELEVATED INTRAOCULAR-PRESSURE

The purpose of this study was to determine the mechanical response of the lamina cribrosa (LC) to elevated intraocular pressure (IOP) so as to identify possible mechanisms of optic nerve damage in early glaucom a. Ten pairs of normal human eyes were fixed after 24 hours' exposure to 50 mm Hg pressure (experimental eyes) or 5 mm Hg pressure (contrala teral control eyes). Photomicrographs of the central region of the opt ic nerve head (ONH) were taken to examine the LC morphologically and t o measure the dimensions of the LC. It was found that elevated IOP cau sed the LC to deflect posteriorly without affecting its thickness. The majority of the posterior displacement in the LC occurred near the pe riphery of the ONH. This shape change is consistent with a model of fo rce distribution within the LC in which shear stresses are dominant; s uch stresses are maximal at the periphery and minimal at the centre of the ONH. These findings support a model in which mechanical forces, s pecifically shearing stresses within the peripheral lamina, play a dir ect role in the pathology of glaucomatous optic neuropathy.