Comparison of phase-resolved Doppler optical coherence tomography and optical coherence tomography angiography for measuring retinal blood vessels size

The goal of this study was to compare two OCT-based methods for measuring retinal blood vessels size: Phase-resolved Doppler OCT (DOCT) and OCT angiography (OCTA). The study was conducted in rats (n= 6) using a SD-OCT system operating at 1060 nm with 92 kHz image acquisition rate. Arteries and veins were separated by the phase polarity. Results from this study showed that the venal diameters are significantly larger than the arterial diameters, and there is no significant difference in the vessel diameters measured by both methods

Correlation of visually evoked intrinsic optical signals and electroretinograms recorded from chicken retina with a combined functional optical coherence tomography and electroretinography system

Akhlagh Moayed, A., Hariri, S., Choh, V., & Bizheva, K. (2012). Correlation of visually evoked intrinsic optical signals and electroretinograms recorded from chicken retina with a combined functional optical coherence tomography and electroretinography system. Journal of Biomedical Optics, 17(1), 0160111–0160115. Copyright 2012 Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. http://dx.doi.org/10.1117/1.JBO.17.1.016011Visually evoked fast intrinsic optical signals (IOSs) were recorded for the first time in vivo from all layers of healthy chicken retina by using a combined functional optical coherence tomography (fOCT) and electroretinography (ERG) system. The fast IOSs were observed to develop within ∼5  ms from the on-set of the visual stimulus, whereas slow IOSs were measured up to 1 s later. The visually evoked IOSs and ERG traces were recorded simultaneously, and a clear correlation was observed between them. The ability to measure visually evoked fast IOSs non-invasively and in vivo from individual retinal layers could significantly improve the understanding of the complex communication between different retinal cell types in healthy and diseased retinas.This work was supported by a research grant from the Natural Sciences and Engineering Research Council of Canada and in-kind contributions from Diagnosys LLC

Improved OCT Human Corneal segmentation Using Bayesian Residual Transform

The inherent poor signal to noise ratio of Optical Coherent Tomography(OCT) is considered as a main limitation of OCT segmentation,particularly because images are sampled quickly, at high resolutions,and in-vivo. Furthermore, speckle noise is generated bythe reflections of the OCT LASER limits the ability of automaticallysegmenting OCT images. This paper presents a novel method toautomatically segment human corneal OCT images. The proposedmethod uses Bayesian Residual Transform (BRT) to build a noiserobust external force map, that guides active contours model to thecorneal data in OCT images. Experimental results show that theproposed method outperforms the classical as well as the state-ofthe-art methods

Impact of contact lens wear on epithelial alterations in keratoconus

Purpose The purpose of this study was to characterize the central epithelial thickness (CET) of penetrating keratoplasty corneal specimens obtained from patients with keratoconus (KC) and correlate the histological patterns with their clinical history.Methods Ex vivo histological imaging was performed to measure CET and total corneal thickness (TCT) in 56 patients with KC. Microscopic slides from penetrating keratoplasty corneal specimens, stained with hematoxylin and eosin were evaluated using bright field microscopy. CET and TCT were measured, and morphological features were studied. Clinical history regarding duration of KC prior to surgery and length of and tolerance to contact lens wear were compared and analyzed. Results The microscopic slides of all patients available for follow up (n = 48) were analyzed and CET and TCT were measured. The histological evaluation revealed 3 distinctive epithelial patterns. Pattern 1 with central hypertrophic and hydropic changes (n = 19) measured 70.89 ± 25.88 μm in CET and 308.63 ± 100.74 μm in TCT; Pattern 2 (n = 14) had not changed, similar to normal epithelium CET and TCT measuring 36.5 ± 7.02 μm and 260.14 ± 87.93 μm respectively. Pattern 3 (n = 15) demonstrated thinner central epithelium characterized by atrophy and focal hydropic changes measuring 19.93 ± 4.60 μm and 268.00 ± 79.39 μm in CET and TCT respectively (all p < 0.0001). The presence of Pattern 2 characterized by similar to normal CET was correlated with the duration of the condition (R = 0.600, p = 0.030). There was a significant difference in the length of CL wear comparing those with patterns 1 and 2 versus 3 (least no. of CL years) (p = 0.05 and p = 0.33 respectivelly). Conclusions Patients with advanced disease have various central corneal epithelial changes detected with histology. Although each central epithelial pattern type was distinctive comparing the 3 patterns, there was no correlation with years of CL wear but only with the duration of the condition.Office of Research of the University of Waterlo

Speckle reduction algorithm for optical coherence tomography based on Interval Type II Fuzzy Set

A novel speckle reduction technique based on soft thresholding of wavelet coefficients using interval type II fuzzy system was developed for reducing speckle noise in Optical Coherence Tomography images. The proposed algorithm is an extension of a recently published method for filtering additive noise by use of type I fuzzy system. Unlike type I, interval type II fuzzy based thresholding filter considers the uncertainty in the calculated threshold and the wavelet coefficient is adjusted based on this uncertainty. Application of this novel algorithm to optical coherence tomography images of a finger tip show reduction in speckle with little edge blurring

A Conditional Random Field Weakly Supervised Segmentation Approach for Segmenting keratocytes Cells in Corneal Optical Coherence Tomography Images

Keratocytes are vital for maintaining the overall health of humancornea as they preserve the corneal transparency and help in healingcorneal injuries. Manual segmentation of keratocytes is challenging,time consuming and also needs an expert. Here, we proposea novel semi-automatic segmentation framework, called ConditionalRandom FieldWeakly Supervised Segmentation (CRF-WSS)to perform the keratocytes cell segmentation. The proposed frameworkexploits the concept of dictionary learning in a sparse modelalong with the Conditional Random Field (CRF) modeling to segmentkeratocytes cells in Ultra High Resolution Optical CoherenceTomography (UHR-OCT) images of human cornea. The resultsshow higher accuracy for the proposed CRF-WSS framework compareto the other tested Supervised Segmentation (SS) andWeaklySupervised Segmentation (WSS) methods

Relationship between vessel diameter and depth measurements within the limbus using ultra-high resolution optical coherence tomography

Purpose: To establish a relationship between the diameter and depth position of vessels in the superior and inferior corneo-scleral limbus using ultra-high resolution optical coherence tomography (UHR-OCT). Methods: Volumetric OCT images of the superior and inferior limbus were acquired from 14 healthy subjects with a research-grade UHR-OCT system. Differences in vessel diameter and depth between superior and inferior limbus were analyzed using repeated measured ANOVA in SPSS and R. Results: The mean (± SD) superior and inferior diameters were 29 ± 18 μm and 24 ± 18 μm respectively, and the mean (± SD) superior and inferior depths were 177 ± 109 μm and 207 ± 132 μm respectively. The superior limbal vessels were larger than the inferior ones (RM-ANOVA, p = 0.004), and the inferior limbal vessels were deeper than the superior vessels (RM-ANOVA, p = 0.041). There was a positive linear association between limbal vessel depth and size within the superior and inferior limbus with Pearson correlation coefficients of 0.803 and 0.754, respectively. Conclusion: This study demonstrated that the UHR-OCT was capable of imaging morphometric characteristics such as the size and depth of vessels in the limbus. The results of this study suggest a difference in the size and depth of vessels across different positions of the limbus, which may be indicative of adaptations to chronic hypoxia caused by the covering of the superior limbus by the upper eyelid. UHR-OCT may be a useful tool to evaluate the effect of contact lenses on the microvascular properties within the limbus

Localized transverse flow measurement with dynamic light scattering line-scan OCT

A novel decorrelation-based approach for measuring localized transverse flow velocity using line-scan (LS) optical coherence tomography (OCT) is proposed. The new approach allows for separation of the flow velocity component along the line-illumination direction of the imaging beam from other orthogonal velocity components, from particle diffusion motion, and from noise-induced distortion in the OCT signal's temporal autocorrelation. The new method was verified by imaging flow in a glass capillary and a microfluidic device and mapping the spatial distribution of the flow velocity within the beam's illumination plane. This method can be extended in the future to map the three-dimensional flow velocity fields for both ex-vivo and in-vivo applications.National Medical Research Council (NMRC)National Research Foundation (NRF)Published versionCanada First Research Excellence Fund; Canadian Institutes of Health Research (446387); Natural Sciences and Engineering Research Council of Canada (312037); National Research Foundation Singapore (NRF2019-THE002-0006); National Medical Research Council (CG/C010A/2017_SERI, MOH-001015-00)

Correlation of Visually Evoked Functional and Blood Flow Changes in the Rat Retina Measured With a Combined OCTþERG System

PURPOSE. To correlate visually evoked functional and blood flow changes in the rat retina measured simultaneously with a combined optical coherence tomography and electroretinography system (OCTþERG). METHODS. Male Brown Norway (n ¼ 6) rats were dark adapted and anesthetized with ketamine/xylazine. Visually evoked changes in the retinal blood flow (RBF) and functional response were measured simultaneously with an OCTþERG system with 3-lm axial resolution in retinal tissue and 47-kHz image acquisition rate. Both single flash (10 and 200 ms) and flicker (10 Hz, 20% duty cycle, 1-and 2-second duration) stimuli were projected onto the retina with a custom visual stimulator, integrated into the OCT imaging probe. Total axial RBF was calculated from circular Doppler OCT scans by integrating over the arterial and venal flow. RESULTS. Temporary increase in the RBF was observed with the 10-and 200-ms continuous stimuli (~1% and~4% maximum RBF change, respectively) and the 10-Hz flicker stimuli (~8% for 1-second duration and~10% for 2-second duration). Doubling the flicker stimulus duration resulted in~25% increase in the RBF peak magnitude with no significant change in the peak latency. Single flash (200 ms) and flicker (10 Hz, 1 second) stimuli of the same illumination intensity and photon flux resulted in~23 larger peak RBF magnitude and~25% larger RBF peak latency for the flicker stimulus. CONCLUSIONS. Short, single flash and flicker stimuli evoked measureable RBF changes with larger RBF magnitude and peak latency observed for the flicker stimuli