Peter Maloca

Advanced Clinical Imaging and Tissue-based Biomarkers of the Eye for Toxicology Studies in Minipigs

There is increased interest to use minipigs in ocular toxicology studies due to their anatomical similarities with human eyes and as a substitute for nonhuman primates. This requires adaptation of enhanced optical coherence tomography (OCT) techniques and of ocular relevant immunohistochemistry (IHC) or in situ hybridization (ISH) markers to porcine eyes. In this study, OCT and OCT angiography (AngioOCT) were performed on adult Göttingen minipigs. To increase structural information on retinal and choroidal vasculature, OCT data were speckle denoized and choroidal blood vessels were segmented with threshold filtering. In addition, we established a set of IHC and ISH markers on Davidson’s fixed paraffin-embedded minipig eyes: neurofilament-160, neuronal nuclei, calretinin, protein kinase C-α, vimentin, glial fibrillary acidic protein, glutamine synthetase, ionized calcium-binding adaptor molecule-1, rhodopsin, synaptophysin, postsynaptic density protein-95, retinal pigment epithelium (RPE)-specific protein-65, von Willebrand factor, α-smooth muscle actin, desmin, and Ki-67, thus enabling visualization of retinal neuronal and glial cells, photoreceptors, synapses, RPE, blood vessels, myocytes, macrophages, or cell proliferation. Using ISH, transcripts of vascular endothelial growth factor A, angiopoietin-2, and endothelial tyrosine kinase were visualized. This article describes for the first time in minipig eyes speckle noise–free OCT, AngioOCT, and a set of IHC/ISH markers on Davidson’s fixed paraffin-embedded tissues and helps to establish the minipig for ocular toxicology and pharmacology studies.

Three-dimensional speckle reduction in optical coherence tomography through structural guided filtering

Abstract. Optical coherence tomography (OCT) is a high-resolution noninvasive technology used in medical imaging for the spatial visualization of biological tissue. Due to its coherent nature, OCT suffers from speckle noise, which significantly degrades the information content of resulting scans. We introduce a new filtering method for three-dimensional OCT images, inspired by film grain removal techniques. By matching structural relatedness along all dimensions, the algorithm builds up vector paths for every voxel in the image volume representing its structural neighborhood. Then, by considering the information redundancy along these paths, our filter is able to reduce speckle noise significantly while simultaneously preserving structural information. This filter exceeds some common three-dimensional denoising algorithms used for OCT images, both in visual rendering quality and in measurable noise reduction. The noise-reduced results allow for improvement in subsequent processing steps, such as image segmentation.

Detecting Early Choroidal Changes Using Piecewise Rigid Image Registration and Eye-Shape Adherent Regularization

Recognizing significant temporal changes in the thickness of the choroid and retina at an early stage is a crucial factor in the prevention and treatment of ocular diseases such as myopia or glaucoma. Such changes are expected to be among the first indicators of pathological manifestations and are commonly dealt using segmentation-based approaches. However, segmenting the choroid is challenging due to low contrast, loss of signal and presence of artifacts in optical coherence tomography (OCT) images. In this paper, we present a novel method for early detection of choroidal changes based on piecewise rigid image registration. In order to adhere to the eye’s natural shape, the regularization enforces the local homogeneity of the transformations in nasal-temporal (x-) and superior-inferior (y-) direction by penalizing their radial differences. We restrict our transformation model to anterior-posterior (z-) direction, as we focus on juvenile myopia, which correlates to thickness changes in the choroid rather than to structural alterations. First, the precision of the method was tested on an OCT scan-rescan data set of 62 healthy Asian children, ages 7 to 13, from a population with a high prevalence of myopia. Furthermore, the accuracy of the method in recognizing synthetically induced changes in the data set was evaluated. Finally, the results were compared to those of manually annotated scans.

Safety and Feasibility of a Novel Sparse Optical Coherence Tomography Device for Patient-Delivered Retina Home Monitoring

Purpose To study a novel and fast optical coherence tomography (OCT) device for home-based monitoring in age-related macular degeneration (AMD) in a small sample yielding sparse OCT (spOCT) data and to compare the device to a commercially available reference device. Methods In this prospective study, both eyes of 31 participants with AMD were included. The subjects underwent scanning with an OCT prototype and a spectral-domain OCT to compare the accuracy of the central retinal thickness (CRT) measurements. Results Sixty-two eyes in 31 participants (21 females and 10 males) were included. The mean age was 79.6 years (age range, 69–92 years). The mean difference in the CRT measurements between the devices was 4.52 μm (SD ± 20.0 μm; range, −65.6 to 41.5 μm). The inter- and intrarater reliability coefficients of the OCT prototype were both >0.95. The laser power delivered was <0.54 mW for spOCT and <1.4 mW for SDOCT. No adverse events were reported, and the visual acuity before and after the measurements was stable. Conclusion This study demonstrated the safety and feasibility of this home-based OCT monitoring under real-life conditions, and it provided evidence for the potential clinical benefit of the device. Translational Relevance The newly developed spOCT is a valid and readily available retina scanner. It could be applied as a portable self-measuring OCT system. Its use may facilitate the sustainable monitoring of chronic retinal diseases by providing easily accessible and continuous retinal monitoring.

High-Performance Virtual Reality Volume Rendering of Original Optical Coherence Tomography Point-Cloud Data Enhanced With Real-Time Ray Casting

Purpose Feasibility testing of a novel volume renders technology to display optical coherence tomography data (OCT) in a virtual reality (VR) environment. Methods A VR program was written in C++/OpenGL to import and display volumetric OCT data in real time with 180 frames per second using a high-end computer and a tethered head-mounted display. Following exposure, participants completed a Simulator Sickness Questionnaire (SSQ) to assess for nausea, disorientation, and oculomotor disturbances. A user evaluation study of this software was conducted to explore the potential utility of this application. Results Fifty-seven subjects completed the user testing (34 males and 23 females). Mean age was 48.5 years (range, 21–77 years). Mean acquired work experience of the 35 ophthalmologists (61.40%) included in the group was 15.46 years (range, 1–37 years). Twenty-nine participants were VR-naïve. The SSQ showed a mean total score of 5.8 (SD = 9.44) indicating that the system was well tolerated and produced minimal side effects. No difference was reported between VR-naïve participants and experienced users. Overall, immersed subjects reported an enjoyable VR-OCT presence effect. Conclusions A usable and satisfying VR imaging technique was developed to display and interact with original OCT data. Translational Relevance An advanced high-end VR image display method was successfully developed to provide new views and interactions in an ultra high-speed projected digital scenery using point-cloud OCT data. This represents the next generation of OCT image display technology and a new tool for patient engagement, medical education, professional training, and telecommunications.

Interdevice variability of central corneal thickness measurement

Purpose To evaluate variability of central corneal thickness measurement (CCT) devices using a hitherto unprecedented number of CCT devices. Methods CCT was measured consecutively in 122 normal corneas of 61 subjects with seven different devices using three distinct measurement technologies: Scheimpflug, Ultrasound, and Optical Coherence Tomography (OCT). Per device deviation from the mean CCT value per eye was used to determine which of the devices performed best, compared to the mean value. Results Cirrus OCT yielded the lowest deviation. Deviations of the individual devices from the mean CCT of each eye were (OS/OD) 12.8±5.0/14.9±9.4 μm for Topcon noncontact specular microscopy (NCSM), 11.3±5.9/10.6±7.3 μm for Pentacam, 10.7±5.2/10.4±4.8 μm for Spectralis OCT, 6.0±3.9/6.2±4.9 μm for Topcon DRI OCT, 5.1±3.4/5.9±10.3 μm for AngioVue OCT, 4.8±4.1/5.7±4.6 μm for US pachymetry, and 4.2±3.2/5.7±4.6 μm for Cirrus OCT. The maximum differences between US pachymetry and the other devices were very high (up to 120 μm). Conclusion Central corneal thickness may be under- or overestimated due to high interdevice variations. Measuring CCT with one device only may lead to inappropriate clinical and surgical recommendations. OCT showed superior results.

Feasibility Study of Subfoveal Choroidal Thickness Changes in Spectral-Domain Optical Coherence Tomography Measurements of Macular Telangiectasia Type 2

Macular Telangiectasia Type 2 (MacTel2) is a disease of the retina leading to a gradual deterioration of central vision. At the onset of the disease a good visual acuity is present, which declines as the disease progresses to cause reading difficulties. In this paper, we present new insights on the vascular changes in MacTel2. We investigated whether MacTel2 progression correlates to changes in the thickness of the choroid. For this purpose, we apply a recently published registration-based approach to detect deviations in the choroid on a dataset of 45 MacTel2 patients. Between 2012 and 2016 these subjects and a control group were measured twice within variable intervals of time in the Moorfields Eye Hospital in the MacTel Natural History Observation and Registry Study. Our results show that in the MacTel2 group the thickness of the choroid increased while in the control group a decrease was noted. Manual expert segmentation and an automated state-of-the-art method were used to validate the results.

MACULAR TELANGIECTASIA TYPE 2: Quantitative Analysis of a Novel Phenotype and Implications for the Pathobiology of the Disease

Purpose: To investigate retinal microcystoid spaces in macular telangiectasia type 2 with spectral domain optical coherence tomography. Methods: Retrospective review of 135 patients enrolled in the MacTel Natural History Observation and Registry Study at Moorfields Eye Hospital, United Kingdom. One hundred seventy-two eyes from 86 patients who had a comparable scan protocol of at least 30 &mgr;m interval were included for analysis. Retinal microcystoid spaces were identified and segmented and metrics analyzed. Results: From 172 eyes of 86 patients, microcystoid spaces were found in 11 eyes (6.4%) from 8 patients (9.3%). The mean number of microcystoid spaces per eye was 12.9 ± 18.2. Most were located in the inner nuclear layer. The inferonasal quadrant of the macula was the least commonly affected region. Microcystoid spaces were distributed entirely within the assumed macular telangiectasia area on blue light reflectance in all but 2 eyes (4 of 142 microcysts). The median diameter of the microcystoid spaces was 31 &mgr;m (range 15 &mgr;m–80 &mgr;m). Conclusion: Microcystoid spaces as a phenotype of macular telangiectasia should be considered in the differentials for microcystic edema. Understanding the pathogenesis of these lesions may provide further insight into the role of Müller cell dysfunction in this disorder.

3D printing of the choroidal vessels and tumours based on optical coherence tomography

T he choroid has the highest blood flow of any structure in the human body with specific hemodynamic regulatory mechanisms that differ from those of the retinal circulation. It is modulated by a strong autonomic input and is largely insensitive to light stimulation and to differences in blood oxygenation (Kur et al. 2012). Detailed imaging of the choroidal layers has recently been facilitated by the introduction of new imaging modalities such as enhanced depth imaging optical coherence tomography (EDI-OCT) and swept source OCT (SSOCT) (Mrejen & Spaide 2013). One of the more important limitations of routine OCT lies with the two-dimensional (2D) display of static images on a computer screen, hampering characterization of clinically important structural features, such as depth and spatio-anatomical localization. This drawback has been circumvented by the advent of threedimensional (3D) imaging techniques that provide detailed and problemoriented information on both the retinal and choroidal compositions, including volume rendering (Spaide 2015). Similar to routine OCT, this technique is restricted to 2D display in computer screens. Recently, a new method has been reported in which printing of OCT data has been described in a patient with an epiretinal membrane (Choi et al. 2016). This study describes for the first time the use of a 3D printing technique, speckle-free 3D choroidal angiography and tumoropsy (Maloca et al., 2016), applied to3Dprintingof choroidalvessels and pigmented choroidal tumours. In this study, retrospective 1050 nm OCT volumes were collected from healthy eyes and eyes with pigmented choroidal tumours to evaluate choroidal vessel architecture and tumour 3D printing. Inclusion criteria were age >18 years, adequate media clarity for fundus imaging, good central fixation and visual acuity >20/20. Exclusion criteria were nystagmus, poor cooperation and dry eye syndrome. All subjects underwent a comprehensive baseline ophthalmologic examination to exclude any potential retinal or choroidal disorders. Written informed consent was obtained from all patients, and approval was attained from the local ethical committee in accordance with the Declaration of Helsinki and in compliance with data protection regulations. All retinal OCT volumes were acquired in nondilated pupils with a SSOCT device (DRI OCT Triton; Topcon, Tokyo, Japan). The SSOCT volume was captured in a 3D scan pattern over a 3 9 3 mm, 6.0 9 6.0 mm or 9 9 12 mm area, respectively, centred on the region of interest (ROI) with 256 B-scans and a scan density of 512 9 256 pixel. Image processing was performed with a previously published 3D speckle-noise removal method with structure preservation (Gyger Cyrill et al. 2014). For choroidal vessel lumen and tumour extraction, the hyporeflective choroidal vessels and hyperreflective tumour structures, respectively, were manually segmented by threshold filtering in the speckle-free OCT volume (IMAGEJ v1.467; ref – Rasband, W.S., IMAGEJ, US National Institutes of Health, Bethesda, MD, USA, https:// imagej.nih.gov/ij/, 1997–2016) by extracting lumen information from the scan volume. The 3D information of the processed choroid was saved as obj-file which was then enhanced by sealing gaps in the mesh or removing obvious artefacts. Ultimately, a 3D printable OCT model was obtained (Fig. 1). Some models were sent for 3D stereolithography printing in transparent resin or constructed from a hardened liquid (i.materialise, i.Materialise HQ, Leuven, Belgium). One model was submerged in a bath of carat gold (24K) to increase robustness and durability. Other models were printed in additive fused deposition modelling using a gypsum powder for testing combined vessel and tumour structure printing, respectively (3d-prototyp.com, Stans, Switzerland). Design specifications for 3D printing included minimum wall thickness of 1 mm, minimum details of 0.5–1 mm and a size of 130 9 200 9 10 mm. In addition, 3D prints of 300 9 300 9 23 and 210 9 390 9 23 mm have been made (Fig. 2). This corresponds to a magnification of up to 70–100 times. Analysis of 3D print models allows a detailed spatio-anatomical characterization of choroidal vessels and their