Diurnal Cycle of Translaminar Pressure in Nonhuman Primates Quantified With Continuous Wireless Telemetry

Abstract

PURPOSE. Recent retrospective clinical studies and animal experiments have suggested that cerebrospinal fluid pressure (CSFP) is important in glaucoma pathogenesis. Intraocular pressure (IOP) and CSFP are the driving components of the translaminar pressure (TLP), which directly effects the optic nerve head. This study measured the diurnal cycle of TLP using continuous wireless telemetry in nonhuman primates (NHPs), a common animal model of glaucoma. METHODS. We have developed an implantable wireless telemetry system based on a small piezoelectric pressure transducer with low drift. Unilateral IOP was measured in the anterior chamber of the eye, and intracranial pressure (ICP, a surrogate measure of CSFP) was measured in the brain parenchyma in four awake, behaving NHPs for periods of 22 to 281 days. IOP and ICP telemetry transducers were calibrated with direct pressure measurements in the eye (every 2 weeks) and brain (monthly). TLP was quantified in real time as IOP-ICP, and hourly means of IOP, ICP, and TLP were analyzed. RESULTS. Results show that mean ICP is significantly higher by an average of 4.8 ± 0.8 mmHg during sleeping hours in NHPs (P < 0.01). IOP showed a small but significant nocturnal elevation in two of four animals despite NHPs sleeping upright (P < 0.05). TLP was significantly lower during sleep (7.1 ± 0.6 mmHg; P < 0.01) than when the animals were awake and active (11.0 ± 0.9 mmHg), driven primarily by the large increase in ICP during sleep. CONCLUSIONS. The 56% increase in TLP during waking hours in NHPs matches the increase in TLP due to postural change from supine to upright reported previously in humans.

Effect of Body Position on Intraocular Pressure (IOP), Intracranial Pressure (ICP), and Translaminar Pressure (TLP) Via Continuous Wireless Telemetry in Nonhuman Primates (NHPs)

“…1 ) based on a small piezoelectric transducer with low temporal drift that accurately measures IOP in the anterior chamber, ICP (as a surrogate for CSFP) in the parenchyma of the brain, and arterial blood pressure (BP) in the lumen of a major artery (BP data are not presented in this study). 37 An in-depth description of the surgical procedure and placement of both the wireless telemetry implant and pressure transducers was described in a recent study. 37 In brief, the IOP transducer was placed in the right eye and the ICP transducer was placed in the right frontal lobe, ∼2.5 cm from the midline of the brain at the same height as the IOP transducer when the animal is upright ( Fig.…”

“… 37 An in-depth description of the surgical procedure and placement of both the wireless telemetry implant and pressure transducers was described in a recent study. 37 In brief, the IOP transducer was placed in the right eye and the ICP transducer was placed in the right frontal lobe, ∼2.5 cm from the midline of the brain at the same height as the IOP transducer when the animal is upright ( Fig. 1 ).…”

“…1 ). 37 The telemetry system wirelessly records 200 measurements of each physiologic pressure per second.…”

“…( E ) Slit lamp photograph of the intraocular placement of the piezoelectric IOP transducer in the anterior chamber relative to the cornea and iris. Reprinted from Jasien et al 37 with permission.…”

“…As previously described, the IOP telemetry transducer was calibrated every two weeks via anterior chamber cannulation manometry with a 27-gauge needle placed through the cornea at the limbus under slit-lamp biomicroscopy. 37 Proparacaine hydrochloride (0.5% ophthalmic solution) was applied to anesthetize the cornea before anterior chamber cannulation. To assess the error in the IOP transducer reading, absolute manometric IOP is elevated from 5 to 30 mm Hg in 5 mm Hg steps, with the 15 mm Hg IOP level used for error calculation.…”