Retinal Vein Pulsation Is in Phase with Intracranial Pressure and Not Intraocular Pressure

Abstract

As efforts to noninvasively measure intracranial pressure (ICP) increase, we thought it important to investigate the timing of retinal venous pulsation in relation to the intraocular and intracranial pressure pulses. Neurosurgical patients undergoing continuous direct ICP monitoring had video recordings of ICP, IOP, and retinal venous pulsation waveforms taken with constant timing relative to the cardiac cycle using pulse oximetry. Video frames of the maxima and minima of these parameters, including retinal vein diameter, were identified. The times from pulse oximetry "beep" to these parameters were measured and converted into a percentage of the respective cardiac cycle. A total of 338 measurements from nine subjects with a mean age of 39 years, mean ICP of 4.4 mm Hg and IOP 15.1 mm Hg were taken. Vein diameter minima occurred an insignificant 0.6% of cardiac cycle before ICP minima (P = 0.6620) and a significant 3.2% after IOP minima (P = 0.0097) and significantly later than IOP (51%) and ICP maxima (74%, all P < 0.0001). Maximum vein diameter occurred an insignificant 2.0% before IOP maxima (P = 0.2267) and was significantly different from IOP and ICP minima (P < 0.00001). Mean venous pulsation pressure between the two eyes was significantly associated with ICP (r = 0.89, P = 0.0075). During pulsation, central retinal vein collapse occurs in time with IOP and ICP diastole. Venous collapse is not induced by intraocular systole. These results suggest that ICP pulse pressure dominates the timing of venous pulsation.