Deformation Response of the Human Lamina Cribrosa to Intracranial Pressure Lowering.

The optic nerve head (ONH) is subjected to both intraocular pressure (IOP) and intracranial pressure (ICP), which act in opposing directions at the lamina cribrosa (LC). 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 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 to calculate the deformation response of the LC in 7 eyes of 7 patients with normal pressure hydrocephalus. 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 Eqz = 0.35%±0.21% (p ≤ 0.031). A larger compressive Ezz was associated with a larger ICP decrease (p = 0.007). Larger Err, Erq , 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).