Deformation Response of the Human Lamina Cribrosa to Intracranial Pressure Lowering

The optic nerve head (ONH) is subjected to both intra-ocular pressure (IOP) and intracranial pressure (ICP). The translaminar pressure difference (TLPD) is defined as the difference between IOP and ICP. A change in TLPD, whether from changes in IOP or ICP, could subject the lamina cribrosa (LC) to altered deformation, potentially damaging the axons, activating the mechanosensitive glial cells, and promoting remodeling of the connective tissue structures in the ONH. In this study, we applied spectral domain optical coherence tomography (SD-OCT) and digital volume correlation (DVC) to calculate the deformation response of the LC in 7 eyes of 7 patients with normal pressure hydrocephalus (NPH). Radial SD-OCT scans centered on the ONH were acquired prior to and after therapeutic extended cerebrospinal fluid (CSF) drainage. IOP was measured immediately before imaging, and ICP was measured at the beginning and end of the drainage procedure. The procedure led to a mean ICP decrease of 11.24±1.84 mmHg and a small, nonsignificant mean IOP increase of 0.67±2.56 mmHg. ICP lowering produced a significant Ezz=-0.50%±0.47%, Err=0.53%±0.48%, and Eθz=0.35%±0.21% (p≤0.031). A larger compressive Ezz was associated with a larger ICP decrease (p=0.007). Larger Err, Erθ, maximum principal strain, Emax and maximum shear strain, Smax in the plane of the radial scans were associated with a larger increase in a calculated TLPD change (p≤0.035).