iStent insertion orientation and impact on trabecular meshwork motion resolved by optical coherence tomography imaging.

Significance: The iStent is a popular device designed for glaucoma treatment, functioning by creating an artificial fluid pathway in the trabecular meshwork (TM) to drain aqueous humor. The assessment of iStent implantation surgery is clinically important. However, current tools offer limited information. Aim: We aim to develop innovative assessment strategies for iStent implantation using optical coherence tomography (OCT) to evaluate the position and orientation of the iStent and its biomechanical impact on outflow system dynamics. Approach: We examined four iStents in the two eyes of a glaucoma patient. Three-dimensional (3D) OCT structural imaging was conducted for each iStent, and a semi-automated algorithm was developed for iStent segmentation and visualization, allowing precise measurement of position and orientation. In addition, phase-sensitive OCT (PhS-OCT) imaging was introduced to measure the biomechanical impact of the iStent on the outflow system quantified by cumulative displacement (CDisp) of pulse-dependent trabecular TM motion. Results: The 3D structural image processed by our algorithm definitively resolved the position and orientation of the iStent in the anterior segment, revealing substantial variations in relevant parameters. PhS-OCT imaging demonstrated significantly higher CDisp in the regions between two iStents compared to locations distant from the iStents in both OD ( p = 0.0075 ) and OS ( p = 0.0437 ). Conclusions: Our proposed structural imaging technique improved the characterization of the iStent's placement. The imaging results revealed inherent challenges in achieving precise control of iStent insertion. Furthermore, PhS-OCT imaging unveiled potential biomechanical alterations induced by the iStent. This unique methodology shows potential as a valuable clinical tool for evaluating iStent implantation.

In-vivo characterization of scleral rigidity in myopic eyes using fundus-pulsation optical coherence elastography.

The sclera plays an important role in the structural integrity of the eye. However, as myopia progresses, the elongation of the eyeball exerts stretching forces on the posterior sclera, which typically happens in conjunction with scleral remodeling that causes rigidity loss. These biomechanical alterations can cause localized eyeball deformation and vision impairment. Therefore, monitoring scleral rigidity is clinically important for the management and risk assessment of myopia. In this study, we propose fundus pulsation optical coherence elastography (FP-OCE) to characterize posterior scleral rigidity in living humans. This methodology is based on a choroidal pulsation model, where the scleral rigidity is inversely associated with the choroidal max strain obtained through phase-sensitive optical coherence tomography (PhS-OCT) measurement of choroidal deformation and thickness. Using FP-OCE, we conducted a pilot clinical study to explore the relationship between choroidal strain and myopia severity. The results revealed a significant increase in choroidal max strain in pathologic myopia, indicating a critical threshold beyond which scleral rigidity decreases significantly. Our findings offer a potential new method for monitoring myopia progression and evaluating therapies that alter scleral mechanical properties.

Multi-channel delay sampling to extend imaging depth in high-speed swept-source OCT systems.

We present a multi-channel delay sampling method to extend imaging depth in high-speed swept-source optical coherence tomography (SS-OCT). A balanced detector captures interference signals, converting them into electrical signals, which are then split into N channels, each with fixed time delays determined by the length of electrical cables. Then, they are digitized by an N-channel acquisition card. A calibration procedure is utilized to compensate for non-uniform phase shifts resulting from fixed time delays. The N-channel signals are merged in k-space and resampled to obtain a linearized spectrum, which increases the sampling rate by a factor of N, thereby extending the ranging distance by N times, all without altering k-clock triggering or sacrificing other imaging performance. The signal-to-noise ratio and sensitivity within the original depth range also have been enhanced. This advancement contributes to the improvement of the overall performance of SS-OCT systems.

Three-dimensional optical coherence digital-null deformography of multi-refractive-surface optics with nanometer sensitivity.

Knowledge of the lens deformation during the reliability test is critical for lens design and fabrication. Refractive surface distorts the optical path of probing light, and poses a great challenge to measuring the test-induced nanoscale changes of all refractive lens surfaces simultaneously. In this work, we present an optical coherence digital-null deformography (ODD). A digital null, i.e., the interference signals (including intensity and phase) of the backscattered probing light from each lens surface, was recorded prior to the test with a phase-sensitive optical coherence tomography (OCT). Then the post-test lens was physically aligned to the digital null by actuating a hexapod iteratively with a digital null alignment (DNA) method, so that the refractive distortion was matched. Finally, the changes between the aligned lens and its digital null were measured with an intensity centroid shift (ICS) at micron scale and a joint wavenumber (k)-depth (z) domain phase shift (kz-PhS) at nanoscale. We demonstrate that the proposed kz-PhS has a sensitivity of 4.15 nm and a range of 5 µm without phase wrapping; and the sensitivities of DNA are z translation 0.04 µm, x/y translation 0.24 µm, tilt 0.0003°, and rotation 0.03°. A lens drop test was performed with ODD. Circumventing refractive distortion by the null measurement, ODD can visualize the test-induced changes of all refractive surfaces non-destructively and simultaneously, and it will greatly facilitate lens design and fabrication.

De-aliased depth-range-extended optical coherence tomography based on dual under-sampling.

We demonstrate a dual under-sampling (DUS) method to achieve de-aliased and depth-range-extended optical coherence tomography (OCT) imaging. The spectral under-sampling can significantly reduce the data size but causes well-known aliasing artifacts. A change in the sampling frequency used to acquire the interference spectrum alters the aliasing period within the output window except for the true image; this feature is utilized to distinguish the true image from the aliasing artifacts. We demonstrate that with DUS, the data size is reduced to 37% at an extended depth range of 24 mm, over which the true depth can be precisely measured without ambiguity. This reduction in data size and precise measuring capability would be beneficial for reducing the acquisition time for OCT imaging in various biomedical and industrial applications.

Reducing substances-enhanced degradation of pollutants by permanganate: The role of in situ formed colloidal MnO2.

Permanganate is one of common oxidants used for organic pollutant abatement in water treatment. This study showed that the degradation rate of bisphenol A (BPA) by permanganate at pH 5.0 in the presence of aniline is much higher than that in the absence of aniline. 2, 5, and 10 µM of aniline enhanced BPA degradation rate by 104%, 326% and 601%, respectively. Colloidal MnO2 was formed through the reduction of permanganate by aniline and contributed to BPA oxidation considerably. The reactivity of MnO2 is sensitive to pH and is high under acidic conditions, resulting in the observed enhancement of aniline on BPA removal by permanganate at pH < 7.0. The role of MnO2 was further confirmed by the relationship of MnO2 formation and BPA/aniline removal, the inhibitory effect of Ca2+ on the oxidation of BPA in the presence of aniline. Besides the aniline/BPA system, the pollutants which react with permanganate rapidly are likely to enhance the degradation of coexisting pollutants which show high reactivity towards MnO2. Due to the reduction of permanganate and stabilization of the in situ formed colloidal MnO2 by water matrix, the oxidation rate of pollutant in real water is higher than that in pure water.