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

Abstract

PURPOSE.To examine the biomechanical deformation of load bearing structures of the optic nerve head (ONH) resulting from raised intracranial pressure, using high definition optical coherence tomography (HD-OCT). The authors postulate that elevated intracranial pressure induces forces in the retrolaminar subarachnoid space that can deform ONH structures, particularly the peripapillary Bruch's membrane (BM) and RPE layers. METHODS.The authors compared HD-OCT optic nerve and peripapillary retinal nerve fiber layer (RNFL) findings in eyes with papilledema caused by raised intracranial pressure to findings in eyes with optic disc swelling caused by optic neuritis and nonarteritic anterior ischemic optic neuropathy (NAION), conditions without intracranial hypertension. The authors measured average thickness of the RNFL and the angle of the RPE/BM at the temporal and nasal borders of the neural canal opening. The angle was measured as positive with inward (toward the vitreous) angulation and as negative with outward angulation. RESULTS. Of 30 eyes with papilledema, 20 eyes (67%) had positive RPE/BM rim angles. One of eight optic neuritis (12%) eyes and 1 of 12 NAION (8%) eyes had positive angulation. In five eyes with papilledema, RNFL thickening increased, three of which developed positive RPE/BM angles. On follow-up, 22 papilledema eyes had a reduction of RNFL swelling, and 17 of these eyes had less positive RPE/BM angulation. CONCLUSIONS. In papilledema, the RPE/BM is commonly deflected inward, in contrast to eyes with NAION or optic neuritis. The RPE/BM angulation is presumed to be caused by elevated pressure in the subarachnoid space, does not correlate with the amount of RNFL swelling, and resolves as papilledema subsides. (Invest Ophthalmol Vis Sci. 2011;52: 6558 -6564) DOI:10.1167/iovs.10-6782 P apilledema is caused by increased intracranial pressure. Histopathologic studies in animal models have shown that elevated pressure within the optic nerve sheath causes stasis of axoplasmic flow and decreased blood flow to axons in the neural canal.1-3 The ensuing optic disc swelling (papilledema) is a consequence of axonal distension of the prelaminar and peripapillary nerve fibers. Vascular congestion, leakage, and ischemia follow the acute axoplasmic flow stasis and are associated with interstitial edema. Although the proximate cause of early edema is stagnant axonal transport, there still remains some uncertainty about the relative effects of compression and ischemia. 1-3Burgoyne et al. 4 and others 5-11 have proposed a conceptual approach that analyzes the optic nerve head (ONH) as a biomechanical structure. They hypothesize that stress (force/ cross-sectional area) and strain (local deformation) on the ONH may be key determinants of axonal, glial, and vascular dysfunction in the pathogenesis and progression of glaucoma. Although the forces acting on the nerve head in papilledema differ from those in glaucoma, the application of biomechanical principles may provide insights about the clinical effects of intracrania...

Automated Quantitation of the Posterior Scleral Flattening and Optic Nerve Protrusion by MRI in Idiopathic Intracranial Hypertension

“…These findings are consistent with recent optical coherence tomography studies demonstrating inward deflection of the peripapillary retinal pigment epithelium layer in papilledema. 16,17 On the basis of these observations and results, the extent of optic nerve protrusion appears to be the more clinically relevant marker for the risk of papilledema in IIH. Because larger protrusion implies larger mechanical stress around the nerve head region, it is likely that shear stress does play a role in the mechanism that leads to papilledema.…”

“…Because larger protrusion implies larger mechanical stress around the nerve head region, it is likely that shear stress does play a role in the mechanism that leads to papilledema. 9,16 The MR measure of NP is a potential objective measure for papilledema severity compared with the subjective Frisen scale. 12 Quantitative assessment of the 2 types of globe deformation in the patients with IIH and control subjects revealed that both GF and NP were significantly correlated with IOP, with the GF measure demonstrating the stronger association.…”

Optical Coherence Tomography for the Radiologist

“…Many clinicians will use instrument-based calipers to determine additional parameters including the height and width of the neural rim tissue and the elevation of the Bruch's membrane opening that are monitored in conditions resulting in disc edema. 11 Similarly, the rim tissue at the optic nerve head can be monitored for small changes through measures of the minimum rim width (MRW; see Fig. 2B).…”

Formation of Macular Inner Nuclear Layer Cysts in Optic Atrophy

“…Subsequent reports noted similar cysts in other types of inflammatory optic neuropathies. 8,9 Balk et al 10 and Sotirchos et al 11 hypothesized that INL cysts were the product of an immune response against aquaporin-4 channel found on Müller cells. Their theory was supported by animal models in which deletion of aquaporin-4 led to induction of retinal inflammation and decreased capacity of Müller cells to regulate osmotic stress.…”