Phase-sensitive optical coherence tomography characterization of pulse-induced trabecular meshwork displacement inex vivononhuman primate eyes

Abstract

Abstract. Glaucoma is a blinding disease for which intraocular pressure (IOP) is the only treatable risk factor. The mean IOP is regulated through the aqueous outflow system, which contains the trabecular meshwork (TM). Considerable evidence indicates that trabecular tissue movement regulates the aqueous outflow and becomes abnormal during glaucoma; however, such motion has thus far escaped detection. The purpose of this study is to describe anovel use of a phase-sensitive optical coherence tomography (PhS-OCT) method to assess pulsedependent TM movement. For this study, we used enucleated monkey eyes, each mounted in an anterior segment holder. A perfusion system was used to control the mean IOP as well as to provide IOP sinusoidal transients (amplitude 3 mmHg, frequency 1 pulse/second) in all experiments. Measurements were carried out at seven graded mean IOPs (5,8,10,20,30,40, and 50 mm Hg). We demonstrate that PhS-OCT is sensitive enough to image/ visualize TM movement synchronous with the pulse-induced IOP transients, providing quantitative measurements of dynamic parameters such as velocity, displacement, and strain rate that are important for assessing the biomechanical compliance of the TM. We find that the largest TM displacement is in the area closest to Schlemm's canal (SC) endothelium. While maintaining constant ocular pulse amplitude, an increase of mean IOP results in a decrease of TM displacement and mean size of the SC. These results demonstrate that the PhS-OCT is a useful imaging technique capable of assessing functional properties necessary to maintain IOP in a healthy range, offering a new diagnostic alternative for glaucoma.

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

“…The PhS-OCT system is based on a spectral domain OCT (SD-OCT) configuration [18,58]. A broadband superluminescent light source with a central wavelength of 1340nm and an effective spectral full-width at half-maximum (FWHM) of 110nm was used to achieve an axial resolution (of theoretically ~7.2 μm in air).…”

“…Our work using PhS-OCT in an ex vivo primate model system [18], demonstrates pulsatile TM motion in response to experimentally controlled IOP transients. Such ex vivo studies have advantages including systematic control of IOP and pulse amplitude.…”

“…In 1998, OCT was first proposed for imaging tissue motion/deformation based on pixelated OCT images, which was generically termed optical coherence elastography (OCE) [8]. Since then, intense efforts have been devoted to exploring OCE's ability to image tissue deformation [9][10][11][12][13][14][15][16][17][18][19][20]. A variety of methods have been developed in OCE for the purpose of assessing soft tissue motion based on either the speckle tracking [8][9][10] or the Doppler principle [11][12][13][14][15][16][17][18][19].…”

“…A variety of methods have been developed in OCE for the purpose of assessing soft tissue motion based on either the speckle tracking [8][9][10] or the Doppler principle [11][12][13][14][15][16][17][18][19]. Of special interest, the phase-based Doppler methods permit quantitative assessment of several physical parameters, such as tissue velocity and strain rate (SR) [11][12][13][14][15][16][17][18][19].…”

“…In order to address the limitations imposed by phase noise and phase wrapping, another OCT technique termed phase-sensitive OCT (PhS-OCT) was developed that proved capable of quantification of tissue motion on the nanometer scale [12,17,18]. The PhS-OCT technique applies a phase-resolved Doppler algorithm along the slow scanning axis by means of calculating the phase shift between successive B-frames, demonstrating a capability to resolve velocities of tissue motion as slow as 2.6nm/s [12], a speed well suited for imaging pulse-induced TM motion in the 1 Hz range.…”