Intracranial Pressure Influences the Behavior of the Optic Nerve Head

Abstract

In this work, the biomechanical responses of the optic nerve head (ONH) to acute elevations in intracranial pressure (ICP) were systematically investigated through numerical modeling. An orthogonal experimental design was developed to quantify the influence of ten input factors that govern the anatomy and material properties of the ONH on the peak maximum principal strain (MPS) in the lamina cribrosa (LC) and postlaminar neural tissue (PLNT). Results showed that the sensitivity of ONH responses to various input factors was region-specific. In the LC, the peak MPS was most strongly dependent on the sclera thickness, LC modulus, and scleral canal size, whereas in the PLNT, the peak MPS was more sensitive to the scleral canal size, neural tissue modulus, and pia mater modulus. The enforcement of clinically relevant ICP in the retro-orbital subarachnoid space influenced the sensitivity analysis. It also induced much larger strains in the PLNT than in the LC. Moreover, acute elevation of ICP leads to dramatic strain distribution changes in the PLNT, but had minimal impact on the LC. This work could help to better understand patient-specific responses, to provide guidance on biomechanical factors resulting in optic nerve diseases, such as glaucoma, papilledema, and ischemic optic neuropathy, and to illuminate the possibilities for exploiting their potential to treat and prevent ONH diseases.

Cerebrospinal Fluid Pressure: Revisiting Factors Influencing Optic Nerve Head Biomechanics

“…Peak strains predicted by the models in this study were slightly above 5%, which is similar to those predicted by comparable models of human 10 , 11 , 32 – 34 , 64 and monkey 58 , 65 LC, and also to some recent measurements in in vivo 56 and ex vivo 66 human and ex vivo porcine 67 eyes. For comparison with experiments it is important to consider that the strains predicted by our models assume the LC to be homogeneous.…”

“…The importance of CSFP has also been identified by two recent computational studies that conducted parametric analysis to investigate the effects of CSFP on ONH biomechanics. 10 , 11 Both studies predicted that increasing CSFP would induce large deformation within the ONH, especially in the retrolaminar neural tissue. The importance of CSFP conforms to its association with susceptibility for optic neuropathy.…”

“…The movement of the optic nerve would be constrained at the point of orbit exit, but the degree and exact nature of the constraints, and how these are transmitted to the ONH region, remain unclear. Elsewhere simulations have assumed completely free 10 , 11 , 30 , 32 or fully constrained 42 optic nerves. Acknowledging this uncertainty, and to avoid a potentially biased decision, we considered CON as a categorical parameter with two levels: a completely free boundary and a boundary with fully constrained displacements.…”

“…The degree to which the optic nerve is constrained is unclear. Elsewhere, modeling studies have been conducted both with a completely free optic nerve boundary 10 , 11 , 30 , 32 and with an optic nerve fully constrained at the end. 42 Preliminary tests suggested that the choice could have important effects on the predicted ONH biomechanics.…”

“… 7 – 9 However, the ONH is exposed not only to IOP from within the globe, but also to cerebrospinal fluid pressure (CSFP) within the subarachnoid space and blood pressure (BP) within the central retinal vessels. CSFP and BP can also potentially influence the biomechanical environment within the ONH, 10 – 13 and thus contribute to determine the susceptibility to glaucoma. In fact, in recent years, evidence has been mounting that the susceptibility to glaucoma may be influenced by CSFP.…”