Deformation of the lamina cribrosa by elevated intraocular pressure.

Abstract

The purpose ofthis 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 glaucoma. Ten In this paper, we seek to complement previous work by a direct morphometric study of the response of the LC in normal human eyes to acute changes in IOP. We feel that this approach has several advantages. Firstly, a morphometric approach allows both the overall shape and the internal architecture of the LC to be evaluated as a function of pressure. This is in contrast with previous studies of the effects of pressure on the LC which focused on positional changes of the anterior surface of the retina at the ONH or on the topography ofthe ONH. Secondly, the use of normal eyes in acute experiments permits potential assessment of the factors initiating axonal damage, since the effect of IOP on a presumably normal ONH can be studied. This is important since ONH architecture in glaucomatous eyes will be substantially different from that ofnormal eyes, owing to degenerative optic neuropathy.The goals of the present work were: (i) to characterise and quantify acute deformations of the LC as a result of elevated IOP; (ii) to formulate a mechanical model of the stress distribution within the LC which is consistent with clinically and experimentally observed patterns of axonal damage in glaucoma; and (iii) to identify features of the LC which might increase the susceptibility of some eyes to glaucomatous damage. The experimental approach was to fix normal human eyes at either high or low pressure and then to compare morphometrically the LC from the low and high pressure groups.Materials and methods Ten pairs of ostensibly normal human eyes (average age 69 years) from which the corneas had been removed for transplantation were obtained within 24 hours post mortem from the Eye Bank of Ontario. The eyes were hemisected at the equator and the vitreous was carefully removed under an operating microscope. This dissection was performed while suspending the eye in a saline bath to prevent the retina from detaching. Each posterior hemisphere was then mounted onto a plastic perfusion dish'4 which sealed it at the equator and allowed it to be pressurised. Briefly, this dish had a small discshaped elevated region with bevelled edges which effectively matched the inner diameter of the globe at the equator. The eye was then clamped in position by a ring whose inner

Optical Coherence Tomography of the Swollen Optic Nerve Head: Deformation of the Peripapillary Retinal Pigment Epithelium Layer in Papilledema

“…This may induce changes in load-bearing connective tissues that results in laminar thinning, peripapillary scleral bowing posteriorly, and expansion of the scleral canal. 4,[25][26][27][28][29][30] Our findings in humans are consistent with experimental studies in dogs. Using confocal scanning laser tomography, 31,32 has shown that intracranial hypertension displaces the optic disc surface and lamina cribosa anteriorly (toward the vitreous), whereas ocular hypertension displaces the disc surface posteriorly.…”

Short-term changes in the optic nerve head and visual field after trabeculectomy

“…We assumed as clinically relevant the changes occurring between moderate and severe glaucoma cases, 15 and we therefore estimated D (the difference between post-and preinterventional RNFL) at 20 microns and s at 40 microns (20). The following formula for continuous, paired data were used:…”

“…They postulated that when IOP was reduced after glaucoma filtering surgery, anterior repositioning of posteriorly displaced lamina cribrosa and simultaneous reformation of neuroretinal tissue would occur. 19,20 Cup shape is a description of the distribution of depth values. Cups with gradually sloping borders tend to have more negative values, and cups with steep sloping walls tend to have less negative or even positive values.…”

Pulsatile shear stress leads to DNA fragmentation in human SH‐SY5Y neuroblastoma cell line

“…Elevated intraocular pressure (IOP) typically accompanies glaucoma. Elevated IOP leads to regions of high shear stress and strain in the lamina cribrosa, the region of the eye where the optic nerve traverses the globe (Zeimer & Chen, 1987;Cahane & Bartov, 1992;Fechtner & Weinreb, 1994;Yan et al 1994). Retinal ganglion cells, which make up the optic nerve, undergo apoptosis upon exposure to elevated IOP in rat (Brubaker, 1996) and rabbit (Quigley et al 1995) models of glaucoma.…”