High-resolution OCT Imaging Research Articles

Exploring Healthy Retinal Aging with Deep Learning.

To study the individual course of retinal changes caused by healthy aging using deep learning. Retrospective analysis of a large data set of retinal OCT images. A total of 85 709 adults between the age of 40 and 75 years of whom OCT images were acquired in the scope of the UK Biobank population study. We created a counterfactual generative adversarial network (GAN), a type of neural network that learns from cross-sectional, retrospective data. It then synthesizes high-resolution counterfactual OCT images and longitudinal time series. These counterfactuals allow visualization and analysis of hypothetical scenarios in which certain characteristics of the imaged subject, such as age or sex, are altered, whereas other attributes, crucially the subject's identity and image acquisition settings, remain fixed. Using our counterfactual GAN, we investigated subject-specific changes in the retinal layer structure as a function of age and sex. In particular, we measured changes in the retinal nerve fiber layer (RNFL), combined ganglion cell layer plus inner plexiform layer (GCIPL), inner nuclear layer to the inner boundary of the retinal pigment epithelium (INL-RPE), and retinal pigment epithelium (RPE). Our counterfactual GAN is able to smoothly visualize the individual course of retinal aging. Across all counterfactual images, the RNFL, GCIPL, INL-RPE, and RPE changed by-0.1 μm ± 0.1 μm,-0.5 μm ± 0.2 μm,-0.2 μm ± 0.1 μm, and 0.1 μm ± 0.1 μm, respectively, per decade of age. These results agree well with previous studies based on the same cohort from the UK Biobank population study. Beyond population-wide average measures, our counterfactual GAN allows us to explore whether the retinal layers of a given eye will increase in thickness, decrease in thickness, or stagnate as a subject ages. This study demonstrates how counterfactual GANs can aid research into retinal aging by generating high-resolution, high-fidelity OCT images, and longitudinal time series. Ultimately, we envision that they will enable clinical experts to derive and explore hypotheses for potential imaging biomarkers for healthy and pathologic aging that can be refined and tested in prospective clinical trials. Proprietary or commercial disclosure may be found after the references.

A Comparative Analysis of Morphology and Dimensions of Functional Blebs following PRESERFLO-Microshunt and XEN-Gel-Stent, a Study Using Anterior Segment OCT.

Evaluation of bleb morphology is a vital part of successful filtration glaucoma surgery. The PRESERFLO-MicroShunt (PRESERFLO) and XEN-Gel-Stent (XEN) are drainage devices implanted using different surgical approaches (ab externo and ab interno, respectively), potentially resulting in distinct bleb morphology. Understanding these morphological differences is essential for postoperative care. In this study, we retrospectively examined functioning blebs following PRESERFLO and XEN implantation using high-resolution anterior segment OCT imaging. Qualitative assessment utilizing the Jenaer Bleb Grading System and quantitative assessment measuring 12 parameters representing bleb dimensions were conducted, and the results were compared between the two groups. A total of 80 eyes from 80 patients were included (41 after PRESERFLO, 39 after XEN). Functioning blebs following PRESERFLO exhibited a higher frequency of hyperreflective tenon changes compared to XEN (31.7% vs. 10.3%, respectively, p = 0.02) and a lower frequency of cavernous changes (17.1% vs. 35.9%, p = 0.05). Additionally, PRESERFLO blebs showed a higher frequency of visible episcleral lakes (92.7% vs. 30.8%, p < 0.001). Furthermore, PRESERFLO blebs demonstrated larger height (2.13 ± 0.5 vs. 1.85 ± 0.6 mm, p = 0.03), width (10.31 ± 2.3 vs. 9.1 ± 2.3 mm, p = 0.02), length (9.13 ± 1.8 vs. 8.24 ± 1.9 mm, p = 0.04), posterior location relative to the limbus (6.21 ± 1.2 vs. 5.21 ± 1.8 mm, p = 0.005), and a thicker bleb wall (1.60 ± 0.5 vs. 1.1 ± 0.4 mm, p = 0.004). Functioning blebs following PRESERFLO and XEN displayed morphological distinctions, likely attributed to variations in surgical techniques (ab externo vs. ab interno) and stent dimensions. These morphological differences should be taken into consideration when evaluating blebs, as they could impact assessments of bleb functionality and influence decisions regarding postoperative interventions.

Intra-operative OCT (iOCT) Super Resolution: a Two-Stage Methodology Leveraging High Quality Pre-operative OCT Scans.

Regenerative therapies have recently shown potential in restoring sight lost due to degenerative diseases. Their efficacy requires precise intra-retinal delivery, which can be achieved by robotic systems accompanied by high quality visualization of retinal layers. Intra-operative Optical Coherence Tomography (iOCT) captures cross-sectional retinal images in real-time but with image quality that is inadequate for intra-retinal therapy delivery. This paper proposes a two-stage super-resolution methodology that enhances the image quality of the low resolution (LR) iOCT images leveraging information from pre-operatively acquired high-resolution (HR) OCT (preOCT) images. First, we learn the degradation process from HR to LR domain through CycleGAN and use it to generate pseudo iOCT (LR) images from the HR preOCT ones. Then, we train a Pix2Pix model on the pairs of pseudo iOCT and preOCT to learn the super-resolution mapping. Quantitative analysis using both full-reference and no-reference image quality metrics demonstrates that our approach clearly outperforms the learning-based state-of-the art techniques with statistical significance. Achieving iOCT image quality comparable to pre-OCT quality can help this medical imaging modality be established in vitreoretinal surgery, without requiring expensive hardware-related system updates.

Comparing Retinal Structure in Patients with Achromatopsia and Blue Cone Monochromacy Using OCT

PurposeTo compare foveal hypoplasia and the appearance of the ellipsoid zone (EZ) at the fovea in patients with genetically confirmed achromatopsia (ACHM) and blue cone monochromacy (BCM).DesignRetrospective, multicenter observational study.ParticipantsMolecularly confirmed patients with ACHM (n = 89) and BCM (n = 33).MethodsWe analyzed high-resolution spectral-domain OCT (SD-OCT) images of the macula from patients with BCM. Three observers independently graded SD-OCT images for foveal hypoplasia (i.e., retention of ≥1 inner retinal layers at the fovea), and 4 observers judged the integrity of the EZ at the fovea, based on an established grading scheme. These measures were compared with previously published data from the patients with ACHM.Main Outcome MeasuresPresence of foveal hypoplasia and EZ grade.ResultsFoveal hypoplasia was significantly more prevalent in ACHM than in BCM (P < 0.001). In addition, we observed a significant difference in the distribution of EZ grades between ACHM and BCM, with grade II EZ being by far the most common phenotype in BCM (61% of patients). In contrast, patients with ACHM had a relatively equal prevalence of EZ grades I, II, and IV. Grade IV EZ was 2.6 times more prevalent in ACHM compared with BCM, whereas grade V EZ (macular atrophy) was present in 3% of both the ACHM and BCM cohorts.ConclusionsThe higher incidence of foveal hypoplasia in ACHM than BCM supports a role for cone activity in foveal development. Although there are differences in EZ grades between these conditions, the degree of overlap suggests EZ grade is not sufficient for definitive diagnosis, in contrast to previous reports. Analysis of additional OCT features in similar cohorts may reveal differences with greater diagnostic value. Finally, the extent to which foveal hypoplasia or EZ grade is prognostic for therapeutic potential in either group remains to be seen, but motivates further study.

Abstract 15508: Random Forest Classifier-incoporated Intravascular Optical Coherence Tomography-fluorescence Lifetime Imaging (oct-flim) Provides Automated Characterization of Key Biochemical Components of Coronary Atherosclerotic Plaques

Introduction: Fluorescence lifetime imaging (FLIm) allows label-free biochemical characterization of atheroma, however, multispectral FLIm produces massive data throughput making image interpretation problematic. We investigated whether machine learning algorithm can be applied to intravascular OCT-FLIm for automated biochemical characterization of coronary plaques. Methods and Results: We built a fully-integrated, high-speed OCT-FLIm system and a low-profile, dual-modal imaging catheter that can provide high-resolution OCT images and correctly co-registered multispectral fluorescence lifetime (FL) readouts: ch.1 and ch.2 FL, and FL intensity ratio (ch.2/ch.1). Rapid intracoronary imaging (10-20 mm/s, 100 rps) was safely performed in atheromatous pigs. There were significant differences in FL measurements according to plaque types (high-risk vs. fibrotic: p&lt;0.001). Multispectral FL measurements sampled selectively from histologically-proven plaque components (lipid, macrophage, lipid+macrophage, SMC) were analyzed. Each component was distinguishable from one another either by difference of FLs or intensity ratio. Random forest classifier (RFC), trained with component-labeled multispectral FL dataset, accurately classified key biochemical components of atherosclerotic plaques. RFC-determined biochemical characteristics of target plaque were consistent across two repeated imaging data (intraclass correlation, p&lt;0.0001) and corroborated closely with those derived from quantitative immunohistochemistries. Conclusions: Our OCT-FLIm incorporating RFC-based systematic multispectral FL analysis could provide high-resolution plaque imaging with automated biochemical characterization in beating coronary environment. The present imaging strategy enabling comprehensive characterization of multiple components of atherosclerotic plaques will open a new avenue in the field of cardiovascular imaging.

Vascular Patterns in Retinitis Pigmentosa on Swept-Source Optical Coherence Tomography Angiography.

Background: Retinitis Pigmentosa (RP) represents a retinal dystrophy with an extremely complex pathogenesis further worsened by the impairment of the retinal vascular supply. The main goal of this study was to identify different vascular patterns in RP, by means of optical coherence tomography angiography (OCTA). Methods: A total of 32 RP patients (16 males, 50%; mean age 45.93 ± 11.4) and 32 healthy age-matched controls (16 males, 50%; age 42.8 ± 11.2). High resolution OCT and OCTA images were obtained from all participants. Several quantitative parameters were extracted both from structural OCT and OCTA images. A post-hoc analysis assessed the relationship between the quantitative OCTA parameters adopted and the following measures: best corrected visual acuity (BCVA), central macular thickness (CMT) and retinal nerve fiber layer (RNFL). Results: Mean LogMAR BCVA was 0.24 ± 0.32 for RP patients and 0.0 ± 0.0 for controls (p < 0.01). CMT, choroidal thickness and RNFL were statistically different between RP and controls (p < 0.01). OCTA parameters showed strong alterations of the retinal vascular network in RP (all p < 0.01). Several statistically significant correlations were also found. Furthermore, a vessel tortuosity cut-off of 4.80 and a vessel rarefaction cut-off of 0.62 enabled the RP cohort to be divided into two significantly different sub-groups in terms of BCVA, RNFL and CMT. Conclusions: Quantitative OCTA parameters help identify vascular abnormalities in RP, separating two different vascular patterns.

Cuticular Drusen: Clinical Phenotypes and Natural History Defined Using Multimodal Imaging

To define the range and life cycles of cuticular drusen phenotypes using multimodal imaging and to review the histologic characteristics of cuticular drusen. Retrospective, observational cohort study and experimental laboratory study. Two hundred forty eyes of 120 clinic patients with a cuticular drusen phenotype and 4 human donor eyes with cuticular drusen (n= 2), soft drusen (n= 1), and hard drusen (n= 1). We performed a retrospective review of clinical and multimodal imaging data of patients with a cuticular drusen phenotype. Patients had undergone imaging with various combinations of color photography, fluorescein angiography, indocyanine green angiography, near-infrared reflectance, fundus autofluorescence, high-resolution OCT, and ultrawide-field imaging. Human donor eyes underwent processing for high-resolution light and electron microscopy. Appearance of cuticular drusen in multimodal imaging and the topography of a cuticular drusen distribution; age-dependent variations in cuticular drusen phenotypes, including the occurrence of retinal pigment epithelium (RPE) abnormalities, choroidal neovascularization, acquired vitelliform lesions (AVLs), and geographic atrophy (GA); and ultrastructural and staining characteristics of druse subtypes. The mean age of patients at the first visit was 57.9±13.4 years. Drusen and RPE changes were seen in the peripheral retina, anterior to the vortex veins, in 21.8% of eyes. Of eyes with more than 5 years of follow-up, cuticular drusen disappeared from view in 58.3% of eyes, drusen coalescence was seen in 70.8% of eyes, and new RPE pigmentary changes developed in 56.2% of eyes. Retinal pigment epithelium abnormalities, AVLs, neovascularization, and GA occurred at a frequency of 47.5%, 24.2%, 12.5%, and 25%, respectively, and were significantly more common in patients older than 60 years of age (all P < 0.015). Occurrence of GA and neovascularization were important determinants of final visual acuity in eyes with the cuticular drusen phenotype (both P< 0.015). Small cuticular drusen typically demonstrated a homogenous ultrastructural appearance similar to hard drusen, whereas fragmentation of the central and basal contents was seen frequently in larger cuticular drusen. Although the ultrastructural characteristics of cuticular drusen appear more similar to those of hard drusen, their lifecycle and macular complications are more comparable with those of soft drusen. Cuticulardrusen phenotype may confer a unique risk for the development of GA and neovascularization.

Anterior Lens Capsule and Iris Thicknesses in Pseudoexfoliation Syndrome

ABSTRACTPurpose: The aim of this study was to evaluate anatomic properties of the lens capsule and iris by anterior segment optical coherence tomography (AS-OCT) in patients with pseudoexfoliation (PEX).Methods: This prospective study included 62 eyes of 62 patients with PEX syndrome and 43 eyes of 43 age- and gender-matched controls. All subjects underwent full ophthalmologic examinations including AS-OCT. Pupillary diameter, midperipheral stromal iris thickness, central and temporal lens capsule thicknesses, and peripheral pseudoexfoliation material thickness on the anterior lens capsule surface were measured and recorded.Results: Mean age was 66.8 ± 9.3 years in the PEX group and 65.5 ± 8.9 years in the control group (p = 0.44). The PEX group consisted of 62 patients: 38 men (61.3%) and 24 women (38.7%); the control group included 43 subjects: 25 men (58.1%) and 18 women (41.9%). Pupillary diameter after pharmacologic mydriasis was 21% smaller in the PEX group than controls. Mean midperipheral iris thickness was 36 ± 7.2 μm (7.8%) thinner in the PEX group than that of control group (p = 0.047). The central anterior capsule was a mean of 3.40 ± 0.51 μm (18%) thicker in the PEX group compared to the control group (p = 0.0001). The temporal anterior lens capsule was a mean of 0.17 ± 0.15 μm thicker in the PEX group compared to the control group (p = 0.81).Conclusions: With high-resolution OCT imaging, it has become possible to evaluate the anterior lens capsule without histologic examination and demonstrate that it is thicker than normal in PEX patients.

In-vivo imaging of the palisades of Vogt and the limbal crypts with sub-micrometer axial resolution optical coherence tomography.

A research-grade OCT system was used to image in-vivo and without contact with the tissue, the cellular structure and microvasculature of the healthy human corneo-scleral limbus. The OCT system provided 0.95 µm axial and 4 µm (2 µm) lateral resolution in biological tissue depending on the magnification of the imaging objective. Cross-sectional OCT images acquired tangentially from the inferior limbus showed reflective, loop-like features that correspond to the fibrous folds of the palisades of Vogt (POV). The high OCT resolution allowed for visualization of individual cells inside the limbal crypts, capillaries extending from the inside of the POV's fibrous folds and connecting to a lateral grid of micro-vessels located in the connective tissue directly below the POV, as well as reflections from individual red blood cells inside the capillaries. Difference in the reflective properties of the POV was observed among subjects of various pigmentation levels of the POV. Morphological features observed in the high resolution OCT images correlated well with histology. The ability to visualize the limbal morphology and microvasculature in-vivo at cellular level can aid the diagnostics and treatment of limbal stem cell dysfunction and dystrophies.

The temporal dynamics of miniscleral contact lenses: Central corneal clearance and centration.

To examine the time course of the reduction in central corneal clearance and horizontal and vertical lens translation (decentration) during miniscleral contact lens wear and the theoretical influence upon the optics of the post-lens tear layer. Repeated high-resolution OCT images were captured over an 8h period of miniscleral contact lens wear (using a rotationally symmetric 16.5mm diameter lens) in 15 young, healthy participants with normal corneae. Central corneal clearance and lens decentration were derived from OCT images using semi-automated image processing techniques. Central corneal clearance decreased exponentially over time, reducing by 76±8μm over 8h. Fifty percent of this reduction occurred within 45min of lens wear and seventy-five percent within 2h, with thinning of the post-lens tear layer plateauing 4h after lens insertion. Lens translation exhibited a similar pattern of change (0.18±0.04mm temporal and 0.20±0.09mm inferior decentration) stabilising 1.5-2h after insertion. The change in the lens fit over time resulted in a small reduction in the power of the post-lens tear layer (-0.12±0.01 D) and induced a prismatic effect of 0.01±0.16 Δ base out and 0.50±0.19 Δ base down relative to the pupil centre. For the miniscleral contact lens studied, horizontal and vertical lens decentration followed an exponential decay over 8h that plateaued approximately 2h after lens insertion, while central post-lens tear layer thinning plateaued after 4h of lens wear.

Intraoperative Optical Coherence Tomography - an Overview of Current Clinical Data for the Application in the Anterior and Posterior Segments

Intraoperative optical coherence tomography (iOCT) represents another milestone in ocular imaging technologies. Now, for the first time, high resolution OCT images are available not only pre- or postoperatively, but also intraoperatively. In recent years, there have been significant advances in iOCT technology - from hand-held probes and mounted systems towards iOCT systems which are fully integrated into the surgical microscope and which provide seamless integration into the workflow. These systems offer high-resolution, intraoperative OCT scans in real-time and provide additional information on microstructures of the retina or the cornea. These findings may even lead to a modification of surgical strategies. Like any other new technology, iOCT technology still has some limitations, such as shadowing from instruments and the lack of eye tracking systems. Therefore, the current state of iOCT technology still requires some skill to track surgical maneuvers in real time. Further research and development will help to solve these limitations in the future. However, even if not required for all surgical procedures, iOCT imaging can already improve safety and control in many surgical procedures on the anterior and posterior segments. This has already been shown in several studies and case series. Particularly in the surgery of vitreomacular traction, peeling of epiretinal membranes (ERM peeling) and macular hole surgery, iOCT offers significant added value. It improves the visualisation of transparent structures and helps to avoid the usage of dyes. In addition the success of the surgical maneuvers can be investigated intraoperatively. In lamellar keratoplasty and glaucoma surgery too, iOCT improves precision and safety. Moreover, iOCT technology may help to achieve further insight into ocular pathologies and a better understanding of the impact of surgical maneuvers on visual rehabilitation. Further prospective studies are however required to evaluate the usefulness of iOCT in various surgical procedures on both, the anterior and posterior segments.

Application of high resolution OCT to evaluate irregularity of Bowman's layer in asymmetric keratoconus.

Irregularity of the Bowman's layer (BL) in keratoconus (KC, sample size (n) = 28) and forme fruste keratoconus (FFKC, n=18) eyes was evaluated. Subjects underwent high resolution OCT imaging (Bioptigen Inc., USA) and corneal tomography (Pentacam v1.20r41, OCULUS Optikgeräte GmbH, Germany). Anterior edge of the BL was segmented. A Bowman's roughness index (BRI) was defined as the sum of the enclosed areas between segmented edge and a smooth 3rd order polynomial fit to the edge. BRI was compared with corneal aberrations, Keratoconus percentage index (KISA), Cone location magnitude index (CLMI) and Belin-Ambrosio enhanced ectasia display overall deviation index (BAD-D). Area under the curve (AUC) was determined with logistic regression (LR). Mean BRI (×10-3 ) was 2.12 mm2 , 1.81 mm2 and 1.7 mm2 in normal (n=26), FFKC and KC eyes, respectively (p<0.001). BAD-D (0.79) and BRI (0.74) had the best AUC for FFKC. By combining BAD-D and BRI, the AUC improved to 0.85 (p=0.01). For KC eyes, KISA (0.94), CLMI (0.88), BAD-D (0.96) and aberrations had comparable AUC (p>0.05). However, LR with BRI and other indices didn't improve the AUC in KC eyes (p>0.05). BRI was significantly reduced in FFKC and KC eyes. It improved the detection of FFKC but not KC eyes.

Optical coherence tomography endoscopic probe based on a tilted MEMS mirror.

This paper reports a compact microendoscopic OCT probe with an outer diameter of only 2.7 mm. The small diameter is enabled by a novel 2-axis scanning MEMS mirror with a preset 45° tilted angle. The tilted MEMS mirror is directly integrated on a silicon optical bench (SiOB). The SiOB provides mechanical support and electrical wiring to the mirror plate via a set of bimorph flexure, enabling a compact probe mount design without the requirement of a 45° slope, which is capable to dramatically reduce the probe size and ease the assembly process. Additionally, the SiOB also provides trenches with properly-designed opening widths for automatic alignment of the MEMS mirror, GRIN lens and optical fiber. The 45°-tilted MEMS mirror plate is actuated by four electrothermal bimorph actuators. The packaged 2.7 mm-diameter probe offers 2-axis side-view optical scanning with a large optical scan range of 40° at a low drive voltage of 5.5 Vdc in both axes, allowing a lateral scan area of 2.2 mm × 2.2 mm at a 3 mm working distance. High-resolution 2D and 3D OCT images of the IR card, ex vivo imaging of meniscus specimens and rat brain slices, in vivo imaging of the human finger and nail have been obtained with a TDOCT system.

OCT imaging with temporal dispersion induced intense and short coherence laser source

Lower coherence length and higher intensity are two indispensable requirements on the light source for high resolution and large penetration depth OCT imaging. While tremendous interest is being paid on engineering various laser sources to enlarge their bandwidth and hence lowering the coherence length, here we demonstrate another approach by employing strong temporal dispersion onto the existing laser source. Cholesteric liquid crystal (CLC) cells with suitable dispersive slope at the edge of 1-D organic photonic band gap have been designed to provide maximum reduction in coherence volume while maintaining the intensity higher than 50%. As an example, the coherence length of a multimode He–Ne laser is reduced by more than 730 times.

光学相干层析成像技术对壁画的检测研究

Based on the michelson interferometer, optical coherence tomography (oct) is a fast, non-contact, coherent optical imaging technology. oct can image the internal microstructure underneath the surface. archaeological objects are valuable and thus require nondestructive testing techniques. oct, as a non-destructive analysis technique, is suitable for testing any part of the mural and other cultural relics. high resolution oct images can provide the detailed information of the paint layer on the surface and the ground layer underneath the surface, which is elusive for traditional techniques. the technique of oct is introduced and the verification experiment of the mural of tang dynasty is carried out. from oct images, defect information of the paint layer on the mural topside and structure underneath the surface can be seen. the information is of great help to the research and repair of the mural. oct can be used in the research and repair of murals as a powerful tool for the researchers. ©, 2015, chinese optical society. all right reserved.

Multimodal instrument for high-sensitivity autofluorescence and spectral optical coherence tomography of the human eye fundus.

In this paper we present a multimodal device for imaging fundus of human eye in vivo which combines functionality of autofluorescence by confocal SLO with Fourier domain OCT. Native fluorescence of human fundus was excited by modulated laser beam (λ = 473 nm, 20 MHz) and lock-in detection was applied resulting in improving sensitivity. The setup allows for acquisition of high resolution OCT and high contrast AF images using fluorescence excitation power of 50-65 μW without averaging consecutive images. Successful functioning of constructed device have been demonstrated for 8 healthy volunteers of different age ranging from 24 to 83 years old.

Single-camera polarization-sensitive full-field optical coherence tomography with polarization switch

We present a single-channel detection-based polarization-sensitive full-field optical coherence tomography (PS-FF-OCT) for simultaneous acquisition of high-resolution OCT and linear retardance images. A linearly polarized sub-10-fs laser was used as a broadband light source for the OCT system. A bi-stable polarization switching device, composed of a ferroelectric liquid crystal cell and an analyzer, was employed to get the horizontal and the vertical polarization components of a full-field interference signal. The time-switched two perpendicular interference signals were sequentially recorded by a single charge-coupled device camera, then processed to extract en-face functional images of a biological sample. The rat tail tendon was imaged ex vivo to confirm the imaging feasibility of the proposed system, which showed axial and transverse resolutions of 2 and 1.3 μm, respectively.

TCT-614 Patient-specific Coronary Stenoses Can Be Modeled Using a Combination of Optical Coherence Tomography and Flow Velocities to Accurately Predict Hyperaemic Pressure Gradients

Computational fluid dynamics (CFD) modeling of patient-specific coronary arteries remain limited by image resolution and the phasic nature of flow. Patient-specific pressure and flow data may overcome these limitations. We applied a 3D reconstruction technique that uses high-resolution OCT imaging

Homotopic, non-local sparse reconstruction of optical coherence tomography imagery

The resolution in optical coherence tomography imaging is an important parameter which determines the size of the smallest features that can be visualized. Sparse sampling approaches have shown considerable promise in producing high resolution OCT images with fewer camera pixels, reducing both the cost and the complexity of an imaging system. In this paper, we propose a non-local approach to the reconstruction of high resolution OCT images from sparsely sampled measurements. An iterative strategy is introduced for minimizing a homotopic, non-local regularized functional in the spatial domain, subject to data fidelity constraints in the k-space domain. The novel algorithm was tested on human retinal, corneal, and limbus images, acquired in-vivo, demonstrating the effectiveness of the proposed approach in generating high resolution reconstructions from a limited number of camera pixels.

Corneal biomechanical characterization from in‐vitro eye inflation, optical coherence tomography and finite element modeling

AbstractPurpose Absolute changes in corneal surface area, volume, apex displacement and limbus deformation during in‐vitro inflation were used to determine biomechanical properties of the corneal tissueMethods Whole‐globe and corneal button inflation experiments were performed on porcine eyes placed in a temperature and humidity controlled chamber. IOP was increased and decreased (15‐55‐15 mmHg) at 5mmHg steps, each time acquiring a 3‐D imaging with a customized spectral anterior segment OCT imaging system. Raw images were corrected from optical and fan distortion. Limbus and apex were detected and the corneal volume and surface area were calculated. The experimental data served as input to optimize a 2D‐axis‐symmetric, viscoelastic finite‐element‐model (with cornea‐limbus‐sclera geometry) written in ANSYS to retrieve elastic (Young’s modulus) and viscoelastic (Prony and retardation time constants) corneal biomechanical properties.Results The experimental corneal response upon inflation was well predicted by the FEM simulations. The central cornea deformed more (the apex raised by 60.8 μm at maximum IOP) than the limbal region (factor 3/4 in radial expansion). The limbus expansion caused a flattening of the angle between cornea and sclera. Mean corneal surface was 226 mm2 and changed less than 1% Poisson’s ratio was found to be 0.49 and Young’s modulus 1.24 MPaConclusion Measuring and understanding corneal biomechanical parameters is important to predict the outcome of different surgical treatments and could be useful to early detection of several corneal pathologies. Quantitative high resolution OCT imaging in combination with FEM simulation allows to accurately determine meaningful mechanical parameters.