Noninvasive Estimation of Intracranial Pressure Using Optic-Disc Venous Pulsation Thresholds

Pulsations and pressure changes in the retinal vein are known to be implicated in glaucoma and are sensitive to changes in both intraocular and intracranial pressures (IOP and ICP). This study evaluates the feasibility and physiological concordance of estimating ICP from spontaneous retinal venous pulsation (SVP) thresholds using noninvasive negative-pressure (NP) goggles and comparing these estimates with reference ICPs measured through manometry during lumbar puncture (LP).

This prospective, single-center pilot study evaluated the capacity of the Ocular Pressure Adjusting Pump (OPAP) to aid in estimating ICP. Adults who were scheduled for clinically indicated LP underwent noninvasive IOP modulation with sealed negative-pressure goggles (OPAP) within 24 hours before LP. An increasing magnitude of NP was applied until SVP was extinguished. Masked examiners determined IOP at the last presence of SVP and first absence of SVP at the optic disc, as measured through the OPAP goggles. Predicted ICP was defined as the midpoint between those 2 IOP values. OPAP measurements were performed twice for each eye: once in an upright seated position and again in the left lateral decubitus (LLD) position. Agreements between OPAP-predicted and LP-measured ICPs were evaluated with a Bland-Altman analysis using 80% limits of agreement (LoA).

Of 15 participants, 11 had visible SVPs that could be extinguished during NP application with OPAP and were included in the analysis. Four participants did not exhibit SVPs at baseline; all had LP-measured ICP exceeding IOP (mean ± SD: 17.6 ± 5.3 and 13.5 ± 1.1 mm Hg, respectively; P < 0.001). For eyes with measurable SVP thresholds, the mean OPAP-predicted ICP was 12.7 ± 3.2 mm Hg in an upright seated position and 17.5 ± 3.1 mm Hg in a lateral position. In the upright analysis, mean bias (predicted-reference ICP) was -0.17 mm Hg with 80% LoA ±6.19 Hg. In the lateral analysis, mean bias was +4.66 mm Hg with 80% LoA ±3.56 mm Hg.

In this pilot feasibility study, SVP-threshold-derived ICP estimates demonstrated minimal bias when OPAP measurements were taken with patients in an upright position and systematic overestimation when OPAP measurements were taken with patients in the LLD position. Conversely, OPAP's ICP estimations demonstrated better consistency (narrower 80% LoAs) with measurements taken in the LLD as compared with upright measurements (wider 80% LoAs). These pilot study findings are exploratory in nature and are not intended to guide individual patient care. Larger studies with standardized positioning and contemporaneous reference measurements are required to define accuracy, identify sources of bias, and demonstrate clinical utility.