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

Abstract

<strong>Purpose.</strong> It is suspected that the abnormalities of aqueous outflow pump composed of trabecular meshwork (TM) and Schlemm’s canal (SC) results in the increased outflow resistance and then elevated intraocular pressure (IOP) in initial glaucoma. In order to explore the casual mechanism and the early diagnosis of glaucoma, the dynamic characterizations of aqueous outflow pump were explored. <br/> <strong>Methods.</strong> As a functional extension of optical coherence tomography (OCT), tissue Doppler OCT (tissue-DOCT) method capable of measuring the slow tissue movement was developed. The tissue-DOCT imaging was conducted on the corneo-scleral limbus of 4 monkey eyes. The eye was mounted in an anterior segment holder, together with a perfusion system to control the mean IOP and to induce the cyclic IOP transients with amplitude 3 mm Hg at frequency 1 pulse/second. IOP was monitored on-line by a pressure transducer. Tissue-DOCT data and pressure data were recorded simultaneously. The IOP-transient induced Doppler velocity, displacement and strain rate of TM and the normalized area of SC were quantified at 7 different mean IOPs (5, 8, 10, 20, 30, 40, 50 mm Hg). <br/> <strong>Results.</strong> The outflow system, including TM, SC and CCs, was visualized in the micro-structural imaging. The IOP-transient induced pulsatile TM movement and SC deformation were detected and quantified by tissue-DOCT. The TM movement was depth-dependent and the largest movement was located in the area closest to SC endothelium (SCE). Both the pulsations of TM and SC were found to be synchronous with the IOP pulse wave. At 8 mm Hg IOP, the global TM movement was around 0.65&mu;m during one IOP transient. As IOP elevated, a gradual attenuation of TM movement and SC deformation was observed. <br/> <strong>Conclusions.</strong> The observed pulsation of TM and SC induced by the pulsatile IOP transients was in good agreement with the predicated role of TM and SC acting as a biomechanical pump (pumping aqueous from anterior chamber into SC and from SC into CCs) in the aqueous outflow system. As the IOP elevated, the attenuated pulsation amplitude of the aqueous outflow pump indicated the failure of the mechanical pump and the increase of aqueous outflow resistance. The promising results revealed the potential of using the proposed tissue-DOCT for diagnosis and associated therapeutic guidance of the initial and progressive glaucoma process by monitoring the pulsation of the outflow pump.