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Murray A. Johnstone, Peng Li, Roberto Reif, Zhongwei Zhi, Lei Shi, Tueng Shen, Elizabeth Martin, Ruikang Wang; Optical Coherence Tomography (OCT) Imaging of Pulse-induced Trabecular Meshwork (TM) Movement Ex Vivo in Non-human Primates. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2743.
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© ARVO (1962-2015); The Authors (2016-present)
Aqueous flows from Schlemm's canal (SC) to the aqueous veins by cyclic pulsatile mechanisms that depend on TM movement(1) and become abnormal in glaucoma(1). We hypothesized that OCT could detect and measure pulse-induced TM movement.
Monkeys (Eye 1: Nemestrina, sex (F), 4.2 y/o, 4.8 kg.) (Eye 2: Fascicularis, F, 15.8 y/o, 7.1 kg. Perfusion system provided pulse waves that were monitored in-line by a pulse transducer. Trigger device synchronized pulse wave and OCT data acquisition. TM movement was measured by an OCT device that had sensitivity to tissue motion at the nanometer (nm) scale. TM displacement was measured at 5 locations: nasal, inferiornasal, inferior, inferiortemporal and temporal in each eye. At 1 site (temporal R eye, nasal L eye), intraocular pressure (IOP) was raised stepwise from 5 to 50 mm, and then lowered stepwise from 50-5 mm Hg while generating an operator-induced pulse (amplitude 3 mm Hg, frequency 1 pulse/second) at each pressure level.
Cyclic waveforms reflective of TM movement detected by OCT were all synchronous with cyclic pulse waves (Fig). Location-dependent TM displacement varied markedly being much greater in the 4.2 y/o: mean = 1,464 ± 706 nm, range (634-2600 nm) than the 15.8 y/o: mean = 357 ± 158 nm, range (171-635 nm) monkey. Ascending and descending TM displacement curves were very similar in individual eyes. Accordingly, measurements at each ascending and descending IOP step were averaged. Pulse-induced TM displacement & Schlemm’s canal size decreased markedly as IOP increased (Fig). Mean TM displacement in nanometers at 5, 8, 10, 20, 30, 40, and 50 mm Hg IOP was in Eye 1: 1117, 550, 406, 173, 42, 26, 24 (r = 0.88; p = 0.017); Eye 2: 869, 654, 341, 247, 155, 113, 109 (r = 0.82; p = 0.042).
In this pilot study, OCT imaging was able to detect and measure pulse-induced TM movement as well as TM displacement differences between limbal locations and between eyes. TM displacement amplitudes decreased markedly as IOP increased and SC lumen progressively closed. TM movement is dependent on properties of TM tissue elasticity and compliance. Non-invasive measurements by OCT permit assessment of these TM functional properties that may be important to maintaining IOP within a normal range.
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