Postural Changes and the Trans–Lamina Cribrosa Pressure Difference: A Pilot Study in Neurosurgical Patients without Glaucoma

Abstract

To evaluate the effect of changes in position in the trans-lamina cribrosa pressure difference (TLCPD) by simultaneously measuring and comparing intracranial pressure (ICP) with intraocular pressure (IOP) in seated and supine positions. Prospective cohort study. Patients admitted to the neurosurgery unit at Toronto Western Hospital with an external ventricular drain placed for ICP monitoring. Exclusion criteria were any ophthalmic surgical procedures within the preceding 6 months, history of glaucoma, and corneal abnormalities affecting IOP measurement. Intraocular pressure and ICP were recorded simultaneously in both the supine and seated positions with the order of positions randomized. Measurements were made 10 minutes after assuming each position. The TLCPD (IOP minus ICP) was calculated for the sitting and supine positions. The paired t test was used to assess significance of differences. The TLCPD. Twenty patients were included in the study. The average age was 54±17 years. Results were similar for left and right eyes. Data are shown for right eyes only. Mean sitting and supine IOPs were 15.3±3.5 mmHg and 15.9±3.7 mmHg, respectively (P= 0.32). Mean sitting and supine ICPs were 12.5±6.8 mmHg and 12.8±5.1 mmHg, respectively (P= 0.66). Mean TLCPD was 3.1±6.0 mmHg in the sitting position and 3.1±7.0 mmHg in the supine position (P= 1.00). Supine TLCPD increased in 10 patients (50%), decreased in 8 patients (40%), and was unchanged in 2 patients (10%). In this pilot study of 20 neurosurgical patients without glaucoma, posture-induced TLCPD changes were variable.