Pulsatile motion of the trabecular meshwork in healthy human subjects quantified by phase-sensitive optical coherence tomography

Abstract

Aqueous leaves the anterior chamber of eye by passing through the trabecular meshwork (TM), a tissue thought to be responsible for increased outflow resistance in glaucoma. Motion assessment could permit characterization of TM biomechanical properties necessary to maintain intra-ocular pressure (IOP) within a narrow homeostatic range. In this paper, we report the first in vivo identification of TM motion in humans. We use a phase-sensitive optical coherence tomography (PhS-OCT) system with sub-nanometer sensitivity to detect and image dynamic pulse-induced TM motion. To permit quantification of TM motion and relationships we develop and apply a phase compensation algorithm permitting removal of the otherwise evitable confounding effects of bulk motion. Twenty healthy human eyes from 10 subjects are imaged. The results permit visualization of pulsatile TM motion visualization by PhS-OCT; correlation with the digital/cardiac pulse is highly significant. The correlation permits assessment of the phase lag and time delay between TM motion and the cardiac pulse. In this study, we find that the digital pulse leads the pulsatile TM motion by a mean phase of 3.53 ± 0.48 rad and a mean time of 0.5 ± 0.14 s in the fundamental frequency. A significant linear relationship is present between the TM phase lag and the heart rate (p value < 0.05). The TM phase lag is also affected by age, the relationship not quite reaching significance in the current study. PhS-OCT reveals pulse-induced motion of the TM that may provide insights into the biomechanics of the tissues involved in the regulation of IOP. 11052-11065 (2008). 14. X. Liang, S. G. Adie, R. John, and S. A. Boppart, "Dynamic spectral-domain optical coherence elastography for tissue characterization," Opt. Express 18(13), 14183-14190 (2010). 15. P. Li, A. Liu, L. Shi, X. Yin, S. Rugonyi, and R. K. Wang, "Assessment of strain and strain rate in embryonic chick heart in vivo using tissue Doppler optical coherence tomography," Phys. Med. Biol. 56 (22), 7081-7092 (2011). 16. P. Li, X. Yin, L. Shi, S. Rugonyi, and R. K. Wang, "In vivo functional imaging of blood flow and wall strain rate in outflow tract of embryonic chick heart using ultrafast spectral domain optical coherence tomography," J. ©2013 Optical Society of America

Complete 360° circumferential gonioscopic optical coherence tomography imaging of the iridocorneal angle

“…Cornea and sclera are on top, iris is on the bottom and the zero-delay line is to the right. At the base of the angle, the highly scattering trabecular meshwork appears as a hyperreflective region [3,7,9,10,13,15]. Fig.…”

“…Previously, external imaging through the corneoscleral limbus with OCT has been used to image the angle and related internal structures [3,[7][8][9][10][11][12][13][14][15] using conventional anterior segment OCT systems. Two scanning methods are typically utilized.…”

Visualization of the ocular pulse in the anterior chamber of the mouse eyein vivousing phase-sensitive optical coherence tomography

“…In contrast, the phase shift ϕ during a time interval τ is inherently sensitive to the subwavelength displacement D of scattering particles in the phase-sensitive OCT (PhS-OCT), 7,8 , according to the relation expressed by ϕ ¼ 4πn∕λ 0 × D, where n is the refractive index of the ocular tissue which is typically 1.36, and λ 0 is the center wavelength used in OCT. The detectable displacement range of this phase-based method is bounded by the system signal-to-noise ratio (SNR) (lower limit, ∼λ 0 ∕4πn ffiffiffiffiffiffiffiffiffi ffi SNR p ) and the π ambiguity (upper limit, ∼λ 0 ∕4n).…”

“…The PhS-OCT system is based on a spectral-domain configuration, similar to the system in Ref. 7. A broadband superluminescent light source with a central wavelength of 850 nm and a spectral bandwidth of 100 nm was used to achieve an axial resolution of ∼3.2 μm in air.…”

“…7,10 In order to visualize the time-variant aOP, M-mode structural and phase images are generated along the center A-line of the Bframe (denoted as x 0 ) as shown in Figs. 2(a) and 2(b).…”