Nov 5, 2018
Ep 30 Talking About Glaucoma - 5Nov2018 JOHNSTONE Murray Pulsatile Flow (mp3)
Welcome back to Talking About Glaucoma, a podcast of indeterminate length and frequency. I’m your host Robert Schertzer, a Glaucoma Specialist from Vancouver, BC Canada. To help produce future shows more frequently, I will no longer include artwork and chapter markings. Hopefully this will get me back on track to publishing new episodes each month this coming year. As always, contact me at email@example.com if you have a glaucoma topic that you would like to discuss with me on a future episode.
In this episode, I talk with Murray Johnstone from Seattle about pulsatile flow through the Trabecular Meshwork and collector channels. We discuss the imaging improvements over the years that have made this possible including the latest phase-based OCT scans that result in nanometre resolution instead of the micrometre resolution of spectral domain scans that most of us are using in clinical practice.
This topic spans decades of work that began prior to his fellowship and resumed around the year 2000 as the imaging technology began to become available to prove the theory. Aqueous outflow drugs increase the outflow pulsatility, not just flow. Goldmann thought the TM was rigid preventing he and Asher from being able to explain the pulsatile nature of the flow. The ocular pulse drives movement of the TM, which is not rigid. The drugs that improve outflow, do so by altering the blood flow to achieve their effect. This is literally a stroke volume.
The theoretical sensitivity to motion is in picometer with the newer phase-based OCTs, that of the movement of electrons in an atom, though practically we achieve nanometer resolution. This is sensitivity of motion of the TM walls, and not the resolution of an image.
How does this flow vary by location within the angle and from moment to moment? This is a live dynamic process. They have published numerous studies in both normal and abnormal outflow patients. Questions to answer include how this flow is altered by laser, meds, stent procedures? Does the act of doing the measurements also alter the flow? It is non-contact and non-invasive therefore should not be altering the flow but white-coat syndrome could have an influence. Perhaps in the future, we can instill a drop in the patient’s eye, measure the change in pulsatile flow, and be able to tell whether a particular medication will actually be effective.
We measure 12 seconds of 31 million seconds in a patient’s year when we check IOP several times per year. By determining pulsatile outflow we have the potential to achieve new diagnostic and treatment options for our patients. This is analogous to how cardiology is using imaging modalities in patient care.
Selected References for this episode related to pulsatile flow:
1. Johnstone MA, Grant WM. Microsurgery of Schlemm’s canal and the human aqueous outflow system. Am J Ophthalmol 1973;76:906-917.
2. Johnstone MA, Grant WG. Pressure-dependent changes in structures of the aqueous outflow system of human and monkey eyes. Am J Ophthalmol 1973;75:365-383.
3. Johnstone MA. Pressure-dependent changes in configuration of the endothelial tubules of Schlemm’s canal. Am J Ophthalmol 1974;78:630-638.
4. Johnstone MA. Pressure-dependent changes in nuclei and the process origins of the endothelial cells lining Schlemm’s canal.
5. Johnstone MA. The aqueous outflow system as a mechanical pump: evidence from examination of tissue and aqueous movement in human and non-human primates. J Glaucoma 2004;13:421-438.
6. Johnstone MA. A New Model Describes an Aqueous Outflow Pump and Explores Causes of Pump Failure in Glaucoma. In: Grehn H, Stamper R, eds. Essentials in Ophthalmology: Glaucoma II. Heidelberg: Springer, 2006
7. Johnstone MA. Aqueous Outflow: The case for a new model. Review of Ophthalmol 2007;14:79-84.
8. Schacknow P, Samples J, eds. Aqueous Veins. The Glaucoma Book. New York: Springer, 2010:65-78.
9. Johnstone M, Martin E, Jamil A. Pulsatile flow into the aqueous veins: manifestations in normal and glaucomatous eyes. Exp Eye Res 2011;92:318-327.
10. Li P, Reif R, Zhi Z, Martin E, Shen TT, Johnstone M, Wang RK. Phase-sensitive optical coherence tomography characterization of pulse-induced trabecular meshwork displacement in ex vivo nonhuman primate eyes. J Biomed Opt 2012;17:076026.
11. Li P, Shen TT, Johnstone M, Wang RK. Pulsatile motion of the trabecular meshwork in healthy human subjects quantified by phase-sensitive optical coherence tomography. Biomed Opt Express 2013;4:2051-2065
12. Johnstone MA, Saheb H, Ahmed II, Samuelson TW, Schieber AT, Toris CB. Effects of a Schlemm canal scaffold on collector channel ostia in human anterior segments. Exp Eye Res 2014;119:70-76.
13. Johnstone MA. Intraocular Pressure Regulation: Findings of Pulse-Dependent Trabecular Meshwork Motion Lead to Unifying Concepts of Intraocular Pressure Homeostasis. J Ocul Pharmacol Ther 2014;30:88-93.
13. Sun Y, Li P, Johnstone M, K W, T S. Pulsatile motion of trabecular meshwork in a patient with iris cyst by phase-sensitive optical coherence tomography. Quantitative Imaging in Medicine and Surgery 2015;5:171-173
14. Xin C, Wang RK, Song S, Shen T, Wen J, Martin E, Jiang Y, Padilla S, Johnstone M. Aqueous outflow regulation: Optical coherence tomography implicates pressure-dependent tissue motion. Exp Eye Res 2017;158:171-186.
15. Carreon T, van der Merwe E, Fellman RL, Johnstone M, Bhattacharya SK. Aqueous outflow - A continuum from trabecular meshwork to episcleral veins. Prog Retin Eye Res 2017;57:108-133.
16. Wang K, Johnstone MA, Xin C, Song S, Padilla S, Vranka JA, Acott TS, Zhou K, Schwaner SA, Wang RK, Sulchek T, Ethier CR. Estimating Human Trabecular Meshwork Stiffness by Numerical Modeling and Advanced OCT Imaging. Invest Ophthalmol Vis Sci 2017;58:4809-4817.
17. Xin C, Song S, Johnstone M, Wang N, Wang RK. Quantification of Pulse-Dependent Trabecular Meshwork Motion in Normal Humans Using Phase-Sensitive OCT. Invest Ophthalmol Vis Sci 2018;59:3675-3681.
This episode was originally recorded March 2016 during the Annual Meeting of the American Glaucoma Society in Ft Lauderdale using two Shure SM58 microphones with a Marantz PMD661 digital recorder. Mixing and sound levelling were FINALLY completed in November 2018 on a MacBook Pro and an iMac using Hindenberg Journalist Pro software. There was a great deal of background noise requiring generous use of noise gate and compression filters, with reverb added back to bring the voices back to life. Narration was overdubbed using a Blue Yeti Microphone with Journalist Pro.
Opinions expressed in this podcast are those of the speakers and are not intended to be taken as the standard of care for glaucoma treatment. Please always weigh the complete clinical picture and involve patients with any decisions in their care.
Murray Johnstone, MD
University of Washington
Department of Ophthalmology
Seattle, WA USA
Robert M Schertzer, MD, MEd, FRCSC
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Theme music “Middle East Gold” ©Daniel Schertzer 2010 and published by Les Prods DOSWA Enr
© 2018 DOSWA Prods Enr/Robert M Schertzer MD. MEd, FRCSC
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