January 2014
Volume 55, Issue 1
Research Highlight  |   January 2014
Toward an Improved Understanding of the Physiology of Aqueous Humor Flow
Investigative Ophthalmology & Visual Science January 2014, Vol.55, 404. doi:https://doi.org/10.1167/iovs.13-13753
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      J. Cameron Millar; Toward an Improved Understanding of the Physiology of Aqueous Humor Flow. Invest. Ophthalmol. Vis. Sci. 2014;55(1):404. doi: https://doi.org/10.1167/iovs.13-13753.

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

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The report by Bogner et al. 1 describes an investigation in living rabbits in which ciliary blood flow (CilBF), IOP, aqueous humor flow (AqF), and effects on these parameters in response to perfusion with arginine vasopressin (AVP) were assessed. In addition, mean arterial blood pressure (MAP) was derived from cannulation of an ear artery, and manipulated via hydraulic occluders placed around the descending thoracic aorta and inferior vena cava, thus altering ocular perfusion pressure. 
Many previous studies have investigated the effect of AVP, analogs, or antagonists (administered by a variety of routes and doses) on various factors selected from IOP, AqF, choroidal blood flow, outflow facility, and systemic blood pressure. Results derived from these studies have been conflicting and, taken as a whole, are challenging to interpret. 
However, the present study represents a first attempt to investigate simultaneously CilBF, AqF, and IOP in relation to how they are influenced dose-dependently by AVP. The results point to a complex relationship between the concentration of AVP reaching the ciliary body/processes, AVP-mediated suppression of ciliary epithelial secretory mechanisms, and effects of reduced CilBF on AqF. For example, a low dose of AVP, which had little effect on CilBF, was found to reduce AqF to a level that, via theoretical considerations, accounted for 76.1% of the observed IOP reduction. By contrast, a higher dose of AVP increased ciliary vascular resistance, while reducing both AqF and CilBF. In this case, the reduction in AqF accounted for 27.6% of the observed IOP reduction, thus implying a relationship between ciliary vascular perfusion and AqF. 
The present work advances this type of investigation to a higher level of sophistication, lends improved clarity to previous observations, and lays important groundwork for further study into the physiological mechanisms responsible for modulating aqueous humor hydrodynamics. 
Bogner B Runge C Strohmaier C The effect of vasopressin on ciliary blood flow and aqueous flow. Invest Ophthalmol Vis Sci . 2014; 55: 396–403. [CrossRef] [PubMed]

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