Flow velocity and pulsatility of the ocular circulation in chronic intracranial hypertension

OBJECTIVES: The aim of this study is to examine the relationship of ocular blood flow velocities and pulsatility to intracranial pressure (ICP). METHODS: We measured arterial and venous flow velocities using color Doppler imaging (CDI) and calculated resistance indices for the central retinal (CRA) and the ophthalmic (OA) arteries from 16 patients (32 eyes) with chronic intracranial hypertension (ICH) and varying degrees of ICP and papilledema. The results were compared with normal data from 16 age-matched, healthy subjects. RESULTS: Arterial flow velocities were significantly decreased for the aggregate subject group compared with controls. A corresponding rise in arterial resistance with increasing ICP in the mild-moderate range was noted. Unexpectedly, with more severe elevations of ICP these trends reversed. CONCLUSIONS: In mild-moderate increased cerebrospinal fluid (CSF) pressure, a reduction of flow velocities may result because of increased vascular resistance. Paradoxically, in more severe chronic ICH, we hypothesize that local autoregulatory vascular changes and/or diversion of cerebral blood flow into the ophthalmic circulation may normalize these parameters. This phenomenon may partially underlie the relative sparing of visual function early in the course of pseudotumor cerebri (PTC), regardless of actual ICP levels.