Retinal Vessel Diameters Change Within 1 Hour of Intracranial Pressure Lowering

Purpose We tested the hypotheses that retinal venule diameter (Dv) is associated with baseline intracranial pressure (ICP) level and that Dv is reduced shortly after ICP lowering. Methods Dv and arteriole diameter (Da) were extracted from scanning laser ophthalmoscopic images in 40 eyes of 20 adult human subjects (10 with and 10 without papilledema) immediately before and after measurement of ICP (range, 10-55 cm H2O) and ICP lowering by cerebrospinal fluid (CSF) drainage via lumbar puncture (LP). Generalized estimating equations (GEE) modeled the relationship between baseline ICP, Da and Dv before LP. Additional GEE modeled the relationship between initial ICP and change in Da and Dv (post-LP - pre-LP) following ICP lowering. Results Test-retest variability of diameter measurements ranged from 0.1 to 2.9 μm (0.1%-2.72%). Neither Da nor Dv pre-LP was associated with baseline ICP level (P = 0.140 Dv, P = 0.914 Da, GEE). Da and Dv change after ICP lowering was associated with baseline ICP, with vessel diameters increasing with lower baseline ICP and decreasing with elevated initial ICP (P = 0.030 baseline ICP vs. Dv change, P = 0.012 baseline ICP vs. Da change, GEE models). Conclusions Retina arteriole and venule diameters change immediately following ICP lowering. The direction of change is dependent on the initial ICP; both increased in subjects with high ICP and both decreased in subjects with normal ICP. Translational Relevance The relationship between initial ICP and direction of retinal vessel size change following ICP lowering suggests a potential effect of ICP on cerebral and ocular hemodynamics that is relevant when considering the use of retinal vessel measurements as a clinical marker of ICP change.