Biomechanical insults to the optic nerve head are thought to contribute to the development and progression of glaucoma. Significant attention has been placed on understanding the IOP-induced deformations within the lamina cribrosa and peripapillary sclera. However, the forces from IOP alone insufficiently characterize the mechanical environment of the lamina cribrosa. Ex vivo and in vivo studies have shown that the acute mechanical strains and pore diameters of the lamina cribrosa are influenced by the interaction between IOP and cerebrospinal fluid pressure (CSFP), or the translaminar pressure (TLP = IOP - CSFP). Increasing clinical evidence also suggests that a lower CSFP, measured via lumbar puncture, increases the risk of primary open-angle and normal-tension glaucoma. Understanding the mechanistic role TLP plays in glaucomatous optic neuropathy requires methods for long-term, continuous and accurate measurement of its constituent pressures in vivo.
Jasien, Downs and colleagues have leveraged their previous experience with continuous telemetric IOP monitoring to engineer and validate an implantable telemetry system capable of simultaneous measurement of IOP, intracranial pressure (ICP as a surrogate for CSFP) and arterial blood pressure. Their approach utilized piezoelectric transducers to continuously capture 15 seconds of pressure data every 150 seconds at 200 Hz to measure the diurnal TLP cycle in four young adult nonhuman primates (NHPs) over relatively long intervals (22 to 281 days). Results show that their NHPs had a 4.2 mm Hg (56%) mean increase in TLP during waking hours compared to sleeping hours and that this increase was largely dictated by a highly consistent decrease in ICP during waking hours. The greater nocturnal ICP seen in NHPs, despite sleeping upright, matches the ICP increase seen in humans when supine during sleeping hours, providing important evidence of the fidelity of their model for future studies investigating the role TLP has in glaucoma pathogenesis. Specifically, the capability of their system to measure these pressures over clinically relevant time intervals has the potential to help unravel the complexities between the TLP gradient (TLP/laminar thickness), laminar remodeling, and glaucoma susceptibility.
The greater nocturnal ICP seen in NHPs, despite sleeping upright, matches the ICP increase seen in humans when supine during sleeping hours