September 2012
Volume 53, Issue 10
Free
Letters to the Editor  |   September 2012
Retinal Vein Pulsation is in Phase with Intracranial Pressure and not Intraocular Pressure
Author Affiliations & Notes
  • Jost B. Jonas
    Department of Ophthalmology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany; and
  • Ningli Wang
    Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
  • Diya Yang
    Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
Investigative Ophthalmology & Visual Science September 2012, Vol.53, 6045. doi:10.1167/iovs.12-10623
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      Jost B. Jonas, Ningli Wang, Diya Yang; Retinal Vein Pulsation is in Phase with Intracranial Pressure and not Intraocular Pressure. Invest. Ophthalmol. Vis. Sci. 2012;53(10):6045. doi: 10.1167/iovs.12-10623.

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      © ARVO (1962-2015); The Authors (2016-present)

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We would like to congratulate Morgan et al. 1 for their important study on the phase of retinal vein pulsations in relation to intracranial pressure. They found a difference in the phasing of the intraocular pressure (IOP) curve and that of the intracranial pressure (ICP) curve with respect to the cardiac cycle, with the ICP curve reaching its height earlier than the IOP curve. They also found that the collapse of the central retinal vein occurred at the time of the minimum of the ICP and IOP (i.e., at the time of the diastole), while the maximal retinal vein diameter was measured at a mean of 2% of the cardiac cycle before the IOP maxima and at a mean of 21% after the ICP maxima. Morgan et al. concluded that the central retinal vein collapse was not induced by the intraocular systole, but that the ICP pulse dominated the timing of venous pulsation. 
In full agreement with their conclusions, we would like to ask whether the importance of the ICP for the retinal vein pulsations, and the phase-shift between the (earlier) ICP pulse and the (later) IOP pulse may help to explain the existence of the retrograde axoplasmic flow, which according to the previous understanding would have had to flow against a pressure gradient from a low-pressure ICP compartment into the high-pressure IOP compartment of the eye. 2 Based on their findings, may one be allowed to postulate that, due to the phase-shift of the (earlier) ICP pulse versus the (later) IOP pulse, for a short, but definite time the ICP may be higher (or at least less lower) than the IOP, helping the retrograde flow to enter the eye? This retrograde pressure shift into the eye could be helpful for the metabolically active transport of the axoplasmic flow into the eye. 
References
Morgan WH Lind CRP Kain S Fatehee N Bala A Yu DY. Retinal vein pulsation is in phase with intracranial pressure and not intraocular pressure. Invest Ophthalmol Vis Sci . 2012;53:4676–4681. [CrossRef] [PubMed]
Quigley HA McKinnon SJ Zack DJ Retrograde axonal transport of BDNF in retinal ganglion cells is blocked by acute IOP elevation in rats. Invest Ophthalmol Vis Sci . 2000;41:3460–3466. [PubMed]
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