In vivo optic nerve head mechanical response to intraocular and cerebrospinal fluid pressure: imaging protocol and quantification method

Abstract

This study presents a quantification method for the assessment of the optic nerve head (ONH) deformations of the living human eye under acute intraocular pressure (IOP) elevation and change of cerebrospinal fluid pressure (CSFP) with body position. One eye from a brain-dead organ donor with open-angle glaucoma was imaged by optical coherence tomography angiography during an acute IOP and CSFP elevation test. Volumetric 3D strain was computed by digital volume correlation. With increase in IOP the shear strain consistently increased in both sitting and supine position (p < 0.001). When CSFP was increased at constant IOP by changing body position, a global reduction in the ONH strain was observed (−0.14% p = 0.0264). Strain in the vasculature was significantly higher than in the structural tissue (+0.90%, p = 0.0002). Retinal nerve fiber layer (RNFL) thickness strongly associated (ρ = −0.847, p = 0.008) with strain in the peripapillary sclera (ppScl) but not in the retina (p = 0.433) and lamina (p = 0.611). These initial results show that: CSFP independently to IOP modulates strain in the human ONH; ppScl strains are greater than strains in lamina and retina; strain in the retinal vasculature was higher than in the structural tissue; In this glaucoma eye, higher ppScl strain associated with lower RNFL thickness.

Pulling and Tugging on the Retina: Mechanical Impact of Glaucoma Beyond the Optic Nerve Head

“…Although the findings in both of these studies represent relatively longer term changes in the position of the retinal vessels in relation to the degree of progressive glaucomatous ONH damage, which may result from remodeling within the retina, they do suggest that forces may be exerted along the retinal vessels as a result of glaucomatous ONH deformation. Additional supporting evidence was reported recently by Fazio et al, 77 who found that upon acutely and independently altering IOP or cerebrospinal fluid pressure in eyes of living human organ donors, biomechanical strains within the peripapillary retina were greatest in magnitude along the vasculature as compared with the neighboring neural retina.…”

“…In order to test the hypothesis that these retinal defects develop as a result glaucomatous ONH deformation and the differential strains it may cause throughout the peripapillary retina, it would be interesting to apply 3D strain mapping techniques to acute and longitudinal deformations captured by OCT. 77,85 With the addition of adaptive-optics and MHz acquisition speeds, OCT can achieve spatial and temporal resolution capable of revealing details and dynamic activity of individual cells within the inner retina. 86 It may someday be possible to study biomechanical strain responses at the cellular level in the living human eye.…”

So-Called Lamina Cribrosa Defects May Mitigate IOP-Induced Neural Tissue Insult

“…We removed the spatial autocorrelation by specifying a rational quadratic spatial correlation structure using the Cartesian distance between the elements in each model. 44 We used α = 0.01 to establish significance. Statistical analysis was done with R 3.5.1 (R Foundation for Statistical Computing, Vienna, Austria).…”

“…First, optical coherence tomography scans show that LC defects are often located at the periphery of the lamina. 14,18,40 Second, evidence from ex vivo 56,[67][68][69][70] and in vivo 44,[71][72][73][74] studies suggest that neural tissues at the periphery of the lamina often experience the largest IOPinduced strains. Modeling defects in this region can provide an upper-bound estimation of the influence of LC defects on IOP-induced mechanical insult to neural tissues.…”

Mechanical Deformation of Human Optic Nerve Head and Peripapillary Tissue in Response to Acute IOP Elevation

“…Recent years have seen important developments in the ability to directly measure ONH deformation, using various imaging modalities including histomorphometry,7 confocal microscopy,8 optical coherence tomography,9,10 microcomputed tomography,11 and second-harmonic generation imaging 12,13. High-resolution images can be generated by using these techniques, but tissue penetration depth and/or displacement resolution are often limited.…”