Biomechanical Responses of Lamina Cribrosa to Intraocular Pressure Change Assessed by Optical Coherence Tomography in Glaucoma Eyes

Abstract

PURPOSE. The purpose of this study was to measure change in anterior lamina cribrosa depth (ALD) globally and regionally in glaucoma eyes at different intraocular pressures (IOP).METHODS. Twenty-seven glaucoma patients were imaged before and after IOP-lowering procedures using optical coherence tomography. The anterior lamina was marked in approximately 25 locations in each of six radial scans to obtain global and regional estimates of ALD. ALD and its change with IOP were compared with optic disc damage, nerve fiber layer thickness, and visual field loss. RESULTS.Variables associated with deeper baseline ALD included larger cup/disc ratio, thinner rim area, larger cup volume, thinner central corneal thickness, and male sex (all P 0.02). When IOP was lowered, ALD position became more anterior, more posterior, or was unchanged. The mean ALD change after lowering was 27 6 142 lm (P ¼ 0.3). The mean absolute value of ALD change was 112 6 90 lm (P ¼ 0.002). Change in ALD was greater in eyes with lower IOP in paired comparisons (P ¼ 0.006) but was not associated with the magnitude of IOP lowering between imaging sessions (P ¼ 0.94). Eyes with no significant change in ALD tended to have more visual field loss than those with significant anterior ALD displacement (P ¼ 0.07). Areas within each optic nerve head that corresponded to zones with thicker nerve fiber layer had greater ALD positional change (P ¼ 0.0007).CONCLUSIONS. The lamina can move either anteriorly or posteriorly with IOP decrease, with greater displacement at lower IOP. Glaucoma eyes and regions within glaucoma eyes associated with greater glaucoma damage exhibited smaller responses.Keywords: glaucoma, lamina cribrosa, optic nerve head, optical coherence tomography, intraocular pressure, biomechanics, stress A major site of damage to retinal ganglion cell (RGC) axons in glaucoma is the optic nerve head (ONH), within the lamina cribrosa.1-3 The biomechanical transmission of stress from intraocular pressure (IOP) produces strain in both the sclera and the ONH, 4-6 generating detrimental effects on RGC axons, ONH astrocytes, and nutritional blood flow in the nerve head. 7 The IOP level that produces RGC loss can be variable among individuals; some eyes suffer damage at IOPs that would be considered normal based on population studies, whereas many eyes with elevated IOP suffer no detectable damage. This suggests that the short-and long-term responses of scleral and ONH connective tissues to changes in IOP represent possible biomarkers for glaucoma incidence and progression. Normal lamina cribrosa structure is remodeled in glaucoma eyes, becoming deeper and wider 8 under the influence of a variety of factors, notably the stress of IOP as delivered through the sclera. 9 The regional differences in connective tissue density and pore size within the lamina cribrosa and greater regional strains suggest that the upper and lower poles of the ONH are weaker at resisting the stress of IOP in both human 10-14 and nonhuman primate eyes. 15 Indeed, these regions contain...

The thick and thin of the central corneal thickness in glaucoma

“…This finding was supported in a subsequent study by Omodaka et al [53]. The disparity may be explained by the duration and severity of glaucoma, which could influence the compliance of the lamina in response to IOP changes [54]. Other studies have found no relationship between CCT and the LC [55,56].…”

Evaluation of Automated Segmentation Algorithms for Optic Nerve Head Structures in Optical Coherence Tomography Images

“…15 Quantitative measurement of nerve fiber layer thickness and ONH structure with OCT 16 now permits detailed examination of LC substructure and its positional movements with change in IOP and intracranial pressure. [17][18][19][20] For digital analysis to be useful in clinical practice and research, automated methods are needed that require minimal observer input.…”

“…21 We previously showed that greater LC deformation with IOP change occurred in clock-hour regions in which there were more remaining nerve fibers. 18 Software to assess lamina change can and should provide regional data as illustrated here, to give a fuller picture of LC remodeling. It will be important to have both normative and glaucoma-specific databases of ALD to assess true abnormality and change.…”

Factors Associated with Lamina Cribrosa Displacement After Trabeculectomy Measured by Optical Coherence Tomography in Advanced Primary Open Angle Glaucoma

“…2 Although a causative link between high intraocular pressure and optic nerve damage is well-established in glaucoma, the exact mechanism remains only partially understood. 3 High IOP and IOP fluctuations cause biomechanical stress and strain that compress, dislocate, stretch and shear the LC.…”

“…4 This leads to a mechanical failure of the load-bearing connective tissues of the ONH, to damage of nearby axons and compromise of the optic nerve head (ONH) blood supply. 2,[4][5][6] The mechanical failure is followed by a posterior bowing and compaction of the LC. 4,7 Patient-specific properties of the LC may explain why some patients are more likely to develop glaucoma damage despite a similar IOP.…”