Aqueous outflow regulation: Optical coherence tomography implicates pressure-dependent tissue motion.
Glaucoma is a leading cause of blindness worldwide and results from damage to the optic nerve. Currently, intraocular pressure is the only treatable risk factor. Changes in aqueous outflow regulate pressure; regulation becomes abnormal in glaucoma. From inside the eye aqueous flows out through the trabecular meshwork into a venous sinus called Schlemm's canal, next into collector channels and finally returns to the episcleral vessels of the venous system. The location of aqueous outflow regulation is unknown. Ex vivo and in vivo studies implicate both pressure-dependent trabecular tissue motion and tissues distal to Schlemm's canal in regulation of aqueous outflow. Technologies have not previously been available to study these issues. New ex vivo imaging in human eyes identifies hinged flaps or leaflets at collector channel entrances using a high-resolution spectral domain optical coherence tomography (SD-OCT) platform. The hinged flaps open and close in synchrony with pressure-dependent trabecular meshwork motion. The SD-OCT platform images from the trabecular meshwork surface while experimentally changing transtrabecular pressure gradients. New in vivo imaging in human eyes uses a motion sensitive technology, phase-sensitive OCT to quantitate real-time pulse-dependent trabecular tissue motion as well as absence of such motion when aqueous access to the outflow system is blocked. The recent studies suggest that aqueous outflow regulation results from synchronous pressure-dependent motion involving a network of interconnected tissues including those distal to Schlemm's canal. The new imaging technologies may shed light on glaucoma mechanisms and provide guidance in the management of medical, laser and surgical decisions in glaucoma.
Department of Bioengineering, University of Washington, USA; Department of Ophthalmology, Beijing Anzhen Hospital, Capital Medical University, China. Electronic address: xinchen0322@gmail.com.
Chen
C
Xin
Department of Bioengineering, University of Washington, USA; Department of Ophthalmology, University of Washington, USA. Electronic address: wangrk@u.washington.edu.
Ruikang K
RK
Wang
Department of Bioengineering, University of Washington, USA. Electronic address: szsong@uw.edu.
Shaozhen
S
Song
Department of Bioengineering, University of Washington, USA; Department of Ophthalmology, University of Washington, USA. Electronic address: ttshen@uw.edu.
Tueng
T
Shen
Department of Ophthalmology, University of Washington, USA. Electronic address: wenjc@uw.edu.
Joanne
J
Wen
Department of Ophthalmology, Cook County Hospital System, USA. Electronic address: martin.elizabethann@gmail.com.
Elizabeth
E
Martin
Department of Ophthalmology, University of Washington, USA. Electronic address: yijiang7@u.washington.edu.
Yi
Y
Jiang
Department of Ophthalmology, University of Washington, USA. Electronic address: smpadilla@uw.edu.
Steven
S
Padilla
Department of Ophthalmology, University of Washington, USA. Electronic address: johnstone.murray@gmail.com.
Murray
M
Johnstone
D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism*; D005902:Glaucoma, Open-Angle / Q000000981:diagnostic imaging / Q000378:metabolism*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D042601:Lymphatic Vessels / Q000000981:diagnostic imaging; D011673:Pulsatile Flow; D041623:Tomography, Optical Coherence / Q000379:methods; D014129:Trabecular Meshwork / Q000000981:diagnostic imaging / Q000378:metabolism*
Aqueous; Collector channels; Glaucoma; Intraocular pressure; Lymphatics; Optical coherence tomography; Pulsatile flow; Schlemm’s canal; Trabecular meshwork