Adoption of faecal immunochemical testing for 2-week-wait colorectal patients during the COVID-19 pandemic: an observational cohort study reporting a new service at a regional centre.

AIM: The COVID-19 pandemic has resulted in the near-complete loss of routine endoscopy services. We describe a major reorganization of service at a regional referral centre (Royal Surrey NHS Foundation Trust) to manage the crisis. Faecal immunochemical testing (FIT) was implemented for triage to make optimum use of limited diagnostic resources. Consultations were switched from face-to-face to telephone. Our aim was to evaluate the impact FIT had on resource allocation and patient diagnoses in the first 3 months of use. METHOD: All colorectal 2-week-wait patient referrals were posted a pack requesting FIT and notification of telephone consultation. A prepaid envelope was included for return of the samples. At consultation, FIT was incorporated with the presenting symptoms to guide the choice of investigation and triage urgency. FIT ≥10 µg/g was interpreted as positive. Outcome data were collected prospectively and compared with retrospective audit data from prepandemic levels across 3 months. RESULTS: From 26 March 2020 to 2 July 381 patients were referred who were invited to provide FIT samples and underwent telephone consultations. Three hundred and fifty eight FIT samples were returned (94%). Onward referral for colonoscopy reduced from 62% to 34% (P < 0.001). There were 14 colorectal cancers (CRC) (3.7%) diagnosed, which was not statistically different from the prepandemic level of 3.9% (P = 0.995). Twelve of the 14 patients with a CRC diagnosis had provided samples; all 12 had FIT ≥10 µg/g and were offered fast-track investigations. CONCLUSIONS: The incorporation of FIT optimized the allocation of limited resources to triage those who required urgent colonic investigation for detecting CRC.

Diagnostic accuracy of point of care faecal immunochemical testing using a portable high-speed quantitative analyser for diagnosis in 2-week wait patients.

AIM: Laboratory-based faecal immunochemical testing (FIT) is the gold standard for detecting the presence of blood in the stool. The aim was to perform a diagnostic accuracy study to confirm if a point of care (POC) analyser for FIT could be safely used as an adjunct in the triage and management of 2-week wait (TWW) colorectal patients. METHODS: The Point of Care Faecal Immunochemical Testing (POC FIT) prospective observational cohort study was designed for TWW patients at a regional referral centre. Between July 2019 and March 2020, patients were invited to perform and bring a FIT sample to clinic. FIT was completed within the clinic appointment using a POC quantitative analyser that has a 2-min processing time (QuikRead go®). Patients and clinicians were blinded to results within the clinic appointment. The results were compared with subsequent diagnostic outcomes. Faecal haemoglobin of <10 µg haemoglobin/g of faeces was considered a negative result. Sensitivities for colorectal cancer (CRC) and combined serious bowel disease (SBD) were calculated using this pre-determined cut-off. RESULTS: A total of 553 patients were included for analytical comparison with diagnostic outcomes. There were 14 (2.5%) patients with CRC and 52 (9.4%) with SBD. The sensitivities for CRC and SBD were 92.9% (95% CI 68.5%-98.7%) and 76.9% (95% CI 63.9%-86.3%) respectively. 379 (68.5%) patients had a negative FIT result (negative predictive value for CRC was 99.7%). CONCLUSIONS: This POC FIT device is a useful adjunct to better manage TWW patients. The high observed sensitivity for CRC offers opportunities, within a single consultation, for improved triage and rationalization of investigation for those with bowel symptoms.

Exascale applications: skin in the game.

As noted in Wikipedia, skin in the game refers to having 'incurred risk by being involved in achieving a goal', where 'skin is a synecdoche for the person involved, and game is the metaphor for actions on the field of play under discussion'. For exascale applications under development in the US Department of Energy Exascale Computing Project, nothing could be more apt, with the skin being exascale applications and the game being delivering comprehensive science-based computational applications that effectively exploit exascale high-performance computing technologies to provide breakthrough modelling and simulation and data science solutions. These solutions will yield high-confidence insights and answers to the most critical problems and challenges for the USA in scientific discovery, national security, energy assurance, economic competitiveness and advanced healthcare. This article is part of a discussion meeting issue 'Numerical algorithms for high-performance computational science'.

In vivo optical imaging of human retinal capillary networks using speckle variance optical coherence tomography with quantitative clinico-histological correlation.

Retinal capillary networks are critically linked to neuronal health and disease. The ability to perform accurate in vivo examination of human retinal capillary networks is therefore valuable for studying mechanisms that govern retinal homeostasis and retinal vascular diseases. Speckle variance optical coherence tomography (svOCT) is a non-invasive imaging technique that has the capacity to provide angiographic information about the retinal circulation. The application of this technology for studying human retinal capillary networks however has not been validated in a quantifiable manner. We use a custom-built svOCT device to qualitatively and quantitatively study the various capillary networks in the human perifovea. Capillary networks corresponding to the nerve fibre layer (NFL), the retinal ganglion cell/superficial inner plexiform layer (RGC/sIPL), the deep inner plexiform layer/superficial inner nuclear layer (dIPL/sINL) and the deep inner nuclear layer (dINL) are imaged in 9 normal human subjects. Measurements of capillary diameter and capillary density are made from each of these networks and results are compared to post-mortem histological data acquired with confocal scanning laser microscopy. Additionally, retinal capillary measurements from high-resolution fundus fluorescein angiogram (FA) are directly compared with svOCT images from 6 eyes. We demonstrate that svOCT images of capillary networks are morphologically comparable to microscopic images of histological specimens. Similar to histological images in svOCT images, the capillaries in the NFL network run parallel to the direction of RGC axons while capillaries in the dINL network comprise a planar configuration with multiple closed loops. Capillaries in remaining networks are convoluted with a complex three-dimensional architecture. We demonstrate that there is no significant difference in capillary density measurements between svOCT and histology images for all networks. Capillary diameter was significantly greater in svOCT images compared to histology for all networks. Capillary density measurements were also higher in svOCT compared to FA. The results of this study suggest that in vivo svOCT imaging allows accurate morphometric assessment of capillary networks in the human perifovea and may provide an improved ability to render microvascular detail compared to FA. Therefore, svOCT may have broad clinical applications in the study of human retinal physiology and disease. The difference in quantitative measurements between svOCT and histology may reflect dynamic variations in the retinal microcirculation and warrants further investigation.

Effects of Myopia and Glaucoma on the Neural Canal and Lamina Cribrosa Using Optical Coherence Tomography.

PRCIS: Glaucoma was associated with axial bowing and rotation of Bruchs membrane opening (BMO) and anterior laminar insertion (ALI), skewed neural canal, and deeper anterior lamina cribrosa surface (ALCS). Longer axial length was associated with wider, longer, and more skewed neural canal and flatter ALCS. PURPOSE: Investigate the effects of myopia and glaucoma in the prelaminar neural canal and anterior lamina cribrosa using 1060-nm swept-source optical coherence tomography. PATIENTS: 19 control (38 eyes) and 38 glaucomatous subjects (63 eyes). MATERIALS AND METHODS: Participants were imaged with swept-source optical coherence tomography, and the images were analyzed for the BMO and ALI dimensions, prelaminar neural canal dimensions, and ALCS depth. RESULTS: Glaucomatous eyes had more bowed and nasally rotated BMO and ALI, more horizontally skewed prelaminar neural canal, and deeper ALCS than the control eyes. Increased axial length was associated with a wider, longer, and more horizontally skewed neural canal and a decrease in the ALCS depth and curvature. CONCLUSION: Our findings suggest that glaucomatous posterior bowing or cupping of lamina cribrosa can be significantly confounded by the myopic expansion of the neural canal. This may be related to higher glaucoma risk associated with myopia from decreased compliance and increased susceptibility to IOP-related damage of LC being pulled taut.

Rapid volumetric OCT image acquisition using compressive sampling.

Acquiring three dimensional image volumes with techniques such as Optical Coherence Tomography (OCT) relies on reconstructing the tissue layers based on reflection of light from tissue interfaces. One B-mode scan in an image is acquired by scanning and concatenating several A-mode scans, and several contiguous slices are acquired to assemble a full 3D image volume. In this work, we demonstrate how Compressive Sampling (CS) can be used to accurately reconstruct 3D OCT images with minimal quality degradation from a subset of the original image. The full 3D image is reconstructed from sparsely sampled data by exploiting the sparsity of the image in a carefully chosen transform domain. We use several sub-sampling schemes, recover the full 3D image using CS, and show that there is negligible effect on clinically relevant morphometric measurements of the optic nerve head in the recovered image. The potential outcome of this work is a significant reduction in OCT image acquisition time, with possible extensions to speeding up acquisition in other imaging modalities such as ultrasound and MRI.

Applications of the polymerase chain reaction in clinical ophthalmology.

Molecular biology has become a valuable component in many areas of medicine, including ophthalmology. Polymerase chain reaction (PCR) is the most widely used tool. It has proven to be a powerful technique in diagnosis and quantification of microorganisms and antibiotic resistance screening. For a growing number of ophthalmic conditions PCR testing can be conducted. It is therefore important that clinicians be knowledgeable about the indications, strengths, and limitations of the technique. The purpose of this review is to explore the current role of PCR in the diagnosis and management of eye disease.

Longitudinal Analysis of Bruch Membrane Opening Morphometry in Myopic Glaucoma.

PRéCIS:: The Bruch membrane opening (BMO) was posteriorly bowed and the degree of nonplanarity increased in stable and progressive glaucoma subjects. BMO became more posterior relative to the Bruch membrane (BM) in control and both stable and progressive glaucoma subjects. PURPOSE: To investigate longitudinal changes in morphologic characteristics of the BMO in control and glaucomatous subjects. MATERIALS AND METHODS: A total of 53 myopic eyes (17 control, 6 suspect, 20 stable glaucoma, and 10 progressing glaucoma) were followed for an average of 4.2±1.4 years and imaged at the baseline and 2 follow-up appointments using a 1060 nm swept-source optical coherence tomography system. BM and BMO were segmented, and 4 morphometric BMO parameters (area, ellipse ratio, nonplanarity, and depth) were measured. RESULTS: There were no significant changes in BMO area or ellipse ratio for all groups. BMO nonplanarity was shown to increase in the glaucoma groups. BMO depth relative to BM increased in all groups except the suspects (control: 8.1 µm/y, P=0.0001; stable glaucoma: 3.5 µm/y, P=0.0001; progressing glaucoma: 14.0 µm/y, P=0.0026). In linear mixed-model analysis, axial length was positively associated with BMO area in all groups except for progressing glaucoma, and with BMO nonplanarity in stable glaucoma. It was not a significant factor to the slopes of the BMO parameters in the ANCOVA analysis of slopes. CONCLUSIONS: Longitudinally, BMO increased in nonplanarity in the glaucoma eyes, and its axial position relative to BM became more posterior in both control and glaucoma eyes.

How does lowering of intraocular pressure protect the optic nerve?

Until recently, the evidence that lowering intraocular pressure (IOP) protects the optic nerve from glaucomatous damage was weak. Several randomized controlled trials have provided stronger evidence that lowering IOP prevents glaucomatous progression. Optic nerves appear to be highly variable in their susceptibility to raised IOP. Elevated IOP likely triggers several parallel, but interacting mechanisms, including direct axonal damage, failure of load-bearing tissues, and disturbances in microvascular supply. The cellular mechanisms that translate these mechanical and physiologic stresses and that lead to excavation of optic nerve tissue are beginning to be understood.

Vascular anatomy of the optic nerve head.

Although intraocular pressure remains the main modifiable risk factor for open-angle glaucoma, other factors such as vascular perfusion likely play a significant role. It is not clear how mechanical deformation, axonal damage, glial responses, and ischemia interact to lead to the tissue remodeling seen clinically as glaucomatous cupping. To understand the potential role of vascular risk factors in glaucoma, it is important to understand the vascular anatomy of the optic nerve head (ONH). The focus of this review is to provide a description of the vascular anatomy of the ONH and to describe recent work in the central nervous system that suggests that astrocytes play a key role in vascular regulation. Finally, the evidence for vascular regulation in the ONH and retina is reviewed.

Microgel particles containing methacrylic acid: pH-triggered swelling behaviour and potential for biomaterial application.

pH-responsive microgels are crosslinked polymer particles that swell when the pH approaches the pK(a) of the ionic monomer incorporated within the particles. In recent work from our group it was demonstrated that the mechanical properties of degenerated intervertebral discs (IVDs) could be restored to normal values by injection of poly(EA/MAA/BDDA) (ethylacrylate, methacrylic acid and butanediol diacrylate) microgel dispersions [J.M. Saunders, T. Tong, C.L. Le Maitre, T.J. Freemont, B.R. Saunders, Soft Matter 3 (2007) 486]. In this work we report the pH dependent swelling and rheological properties of poly(MMA/MAA/EGDMA) (methylmethacrylate and ethyleneglycol dimethacrylate) microgel dispersions. This system was investigated because it contains monomers that are already used as biomaterials. The poly(MMA/MAA/EGDMA) particles exhibit pH-triggered volume swelling ratios of up to ca. 250. The swelling onset for these particles occurs at pH values greater than ca. 6.0. A pK(a) for these particles of ca. 6.7 is consistent with titration and swelling data. Fluid-to-gel phase diagrams for concentrated poly(MMA/MAA/EGDMA) dispersions were determined as a function of polymer volume fraction and pH using tube-inversion measurements. The rheological properties for the gelled microgel dispersions were investigated using dynamic rheology measurements. The elastic modulus data for the poly(MMA/MAA/EGDMA) gelled dispersions were compared to data for poly(EA/MAA/BDDA) microgels. A similar pH-dependence for the elastic modulus was apparent. The maximum elastic modulus was achieved at a pH of about 7.0. The elastic modulus is an exponentially increasing function of polymer volume fraction at pH 7.0. Preliminary cell challenge experimental data are reported that indicate that gelled poly(MMA/MAA/EGDMA) microgel dispersions are biocompatible with cells from human intervertebral discs. However, the duration over which these experiments could be performed was limited by gradual redispersion of the gelled microgel dispersions. Based on the results presented it is suggested that poly(MMA/MAA/EGDMA) microgel would be a good candidate as a biomaterial for structural support of soft connective tissues.

Comparison of silicone and polypropylene Ahmed glaucoma valves: two-year follow-up.

BACKGROUND: To compare the safety and efficacy of silicone and polypropylene Ahmed glaucoma drainage devices. METHODS: We studied a retrospective consecutive case series of 91 eyes of 81 patients who were implanted with Ahmed valves by a single surgeon (R.M.S.). The first 43 eyes received polypropylene (model S2) valves; the remaining 48 eyes received silicone (model FP7) valves. Data collection included demographics, type of glaucoma, and sequential measurement of clinical characteristics. The mean outcome measures were visual acuity, intraocular pressure (IOP), number of antiglaucoma medications, and postoperative complications. Data were collected on day 1; weeks 1, 2-3, and 6; months 3-4, 6, and 12; and last visit. RESULTS: Mean follow-up was 27.1 months for the polypropylene valve and 20.1 months for the silicone valve. Mean decrease in IOP at 1 year was significantly greater in the silicone group than in the polypropylene group (t test, p < 0.005); however, this difference disappeared at 2 years. There were no differences between the groups in visual acuity, number of antiglaucoma medications, bleb needlings with 5-fluorouracil, or minor complications. A greater number of serious complications, including valve failures, occurred in the polypropylene group than in the silicone group, and this difference could not be accounted for by the longer follow-up in the polypropylene group. At 2 years follow-up, 82% of patients with silicone valves and 72% of patients with polypropylene valves continued to achieve greater than 30% IOP reduction. INTERPRETATION: Both the silicone and polypropylene Ahmed valves significantly reduced IOP over 2 years. The silicone valve was associated with fewer serious complications.

Anterior Segment Optical Coherence Tomography for Targeted Transconjunctival Suture Placement in Overfiltering Trabeculectomy Blebs.

PURPOSE: To demonstrate the utility of swept-source anterior segment optical coherence tomography (SS-AS-OCT) in guiding placement of transconjunctival sutures in hypotonous patients after a trabeculectomy. PATIENTS AND METHODS: This is a longitudinal case series of 10 eyes from 10 patients who required transconjunctival sutures after a trabeculectomy. SS-AS-OCT was used to aid in the placement of the sutures to improve the function of the overfiltering bleb. RESULTS: SS-AS-OCT reliably identified localized areas of overfiltering, allowing for targeted suture placement in 8 eyes. The 2 eyes in which localized areas of overfiltering were not found required further surgical intervention. CONCLUSIONS: SS-AS-OCT enhances transconjunctival suturing for overfiltering blebs when focal fluid accumulation is visualized.

Quantifying Variability in Longitudinal Peripapillary RNFL and Choroidal Layer Thickness Using Surface Based Registration of OCT Images.

PURPOSE: To assess within-subject variability of retinal nerve fiber layer (RNFL) and choroidal layer thickness in longitudinal repeat optical coherence tomography (OCT) images with point-to-point measurement comparison made using nonrigid surface registration. METHODS: Nine repeat peripapillary OCT images were acquired over 3 weeks from 12 eyes of 6 young, healthy subjects using a 1060-nm prototype swept-source device. The RNFL, choroid and the Bruch's membrane opening (BMO) were segmented, and point-wise layer thicknesses and BMO dimensions were measured. For each eye, the layer surfaces of eight follow-up images were registered to those of the baseline image, first by rigid alignment using blood vessel projections and axial height and tilt correction, followed by nonrigid registration of currents-based diffeomorphisms algorithms. This mapped all follow-up measurements point-wise to the common baseline coordinate system, allowing for point-wise statistical analysis. Measurement variability was evaluated point-wise for layer thicknesses and BMO dimensions by time-standard deviation (tSD). RESULTS: The intraclass correlation coefficients (ICCs) of BMO area and eccentricity were 0.993 and 0.972, respectively. Time-mean and tSD were computed point-wise for RNFL and choroidal thickness and color-mapped on the baseline surfaces. tSD was less than two coherence lengths of the system 2ℓ = 12 µm at most vertices. High RNFL thickness variability corresponded to the locations of retinal vessels, and choroidal thickness varied more than RNFL thickness. CONCLUSIONS: Our registration-based end-to-end pipeline produced point-wise correspondence among time-series retinal and choroidal surfaces with high measurement repeatability (low variability). Blood vessels were found to be the main sources contributing to the normal variability of the RNFL thickness measure. The computational pipeline with a measurement of normal variability can be used in future longitudinal studies to identify changes that are above the threshold of normal point-wise variability and track localized changes in retinal layers in high spatial resolution. TRANSLATIONAL RELEVANCE: Using the registration-based approach presented in this study, longitudinal changes in retinal and choroidal layers can be detected with higher sensitivity and spatial precision.

Age and Glaucoma-Related Characteristics in Retinal Nerve Fiber Layer and Choroid: Localized Morphometrics and Visualization Using Functional Shapes Registration.

Optical coherence tomography provides high-resolution 3D imaging of the posterior segment of the eye. However, quantitative morphological analysis, particularly relevant in retinal degenerative diseases such as glaucoma, has been confined to simple sectorization and averaging with limited spatial sensitivity for detection of clinical markers. In this paper, we present point-wise analysis and visualization of the retinal nerve fiber layer and choroid from cross-sectional data using functional shapes (fshape) registration. The fshape framework matches two retinas, or generates a mean of multiple retinas, by jointly optimizing the surface geometry and functional signals mapped on the surface. We generated group-wise mean retinal nerve fiber layer and choroidal surfaces with the respective layer thickness mapping and showed the difference by age (normal, younger vs. older) and by disease (age-matched older, normal vs. glaucomatous) in the two layers, along with a more conventional sector-based analysis for comparison. The fshape results visualized the detailed spatial patterns of the differences between the age-matched normal and glaucomatous retinal nerve fiber layers, with the glaucomatous layers most significantly thinner in the inferior region close to Bruch's membrane opening. Between the young and older normal cases, choroid was shown to be significantly thinner in the older subjects across all regions, but particularly in the nasal and inferior regions. The results demonstrate a comprehensive and detailed analysis with visualization of morphometric patterns by multiple factors.

Protocolo ERAS® en cirugía colorrectal / ERAS® in Colorectal Surgery

RESUMEN El protocolo de recuperación optimizada Enhanced Recovery After Surgery (ERAS®) en cirugía colo rrectal promueve un retorno más rápido a la función orgánica siguiendo la evidencia de las últimas investigaciones dirigidas a disminuir el estrés quirúrgico. La vía perioperatoria recomendada está per feccionada, es dinámica y se ajusta a las últimas investigaciones basadas en la evidencia para mejorar todos los aspectos de la atención quirúrgica del paciente. En este artículo describiremos los cuatro aspectos de un paciente a quien se le realizará una cirugía colorrectal: preadmisión, preoperatorio, in traoperatorio y posoperatorio El tema recurrente es disminuir el estrés fisiológico general relacionado con la cirugía; para ello, las intervenciones se superponen a lo largo del recorrido que hace el paciente. Utilizando un enfoque multidisciplinario, la adherencia al protocolo ERAS® en cirugía colorrectal cum pliendo con el 70% o más de las intervenciones de ERAS® ha demostrado una reducción del riesgo de muerte relacionada con el cáncer del 42% a los 5 años. Las intervenciones óptimas no solo se determi nan mediante la publicación de investigaciones de alta calidad, sino que la colaboración internacional periódica permite compartir experiencias e investigaciones y estandarizar los cuidados.

ABSTRACT Enhanced Recovery After Surgery (ERAS®) in colorectal surgery is a protocol that promotes quicker return to function. It follows the latest evidence-based research to promote stress reduction related to surgery. The recommended perioperative pathway is fine-tuned, dynamic and in line with the latest evidence-based research to enhance all aspects of the patient's surgical care. We describe the four aspects for a patient undergoing colorectal surgery - pre-admission, pre-operative, intra-operative and post-operative. The running theme is to reduce overall physiological stress related to surgery and interventions overlap throughout the patient's pathway. Using a multidisciplinary approach, adheren ce to ERAS® in colorectal surgery with ≥70 % compliance to the ERAS interventions has shown a risk reduction of 5-year cancer-related death by 42%. The optimum interventions are not only determined through the publication of high-quality research, but regular international collaboration enables expe rience and research to be shared and care standardized.

Retinal optical coherence tomography at 1 µm with dynamic focus control and axial motion tracking.

High-resolution optical coherence tomography (OCT) retinal imaging is important to noninvasively visualize the various retinal structures to aid in better understanding of the pathogenesis of vision-robbing diseases. However, conventional OCT systems have a trade-off between lateral resolution and depth-of-focus. In this report, we present the development of a focus-stacking OCT system with automatic focus optimization for high-resolution, extended-focal-range clinical retinal imaging by incorporating a variable-focus liquid lens into the sample arm optics. Retinal layer tracking and selection was performed using a graphics processing unit accelerated processing platform for focus optimization, providing real-time layer-specific en face visualization. After optimization, multiple volumes focused at different depths were acquired, registered, and stitched together to yield a single, high-resolution focus-stacked dataset. Using this system, we show high-resolution images of the retina and optic nerve head, from which we extracted clinically relevant parameters such as the nerve fiber layer thickness and lamina cribrosa microarchitecture.

Quantitative Optical Coherence Tomography Angiography of Radial Peripapillary Capillaries in Glaucoma, Glaucoma Suspect, and Normal Eyes.

PURPOSE: To evaluate the quantitative characteristics of the radial peripapillary capillary (RPC) network in glaucoma, glaucoma suspect, and normal eyes using speckle variance optical coherence tomography angiography (OCT-A). To determine correlations between RPC density, nerve fiber layer (NFL) thickness, and visual field indices. DESIGN: Cross-sectional study. METHODS: OCT-A images of RPCs were acquired at a single institution using a custom-built 1060 nm system from 3 groups: unilateral glaucoma (10 eyes from 5 subjects), glaucoma suspects (6 eyes from 3 subjects), and normal control eyes (16 eyes from 9 normal subjects). Peripapillary NFL thickness measurements were determined using spectral-domain optical coherence tomography. Glaucoma and glaucoma suspects also underwent automated 30-2 Humphrey visual field analysis. Manual tracing techniques were used to quantify RPC density in the OCT-A images. Data were analyzed using a linear mixed model with 1 fixed-effect covariate. Correlations between main outcome measures (RPC density, NFL thickness, and visual field index) were determined. RESULTS: Mean age was not significantly different between the 3 groups (P = .25). The density of RPCs was significantly lower in glaucomatous eyes compared with matched-peripapillary regions in the fellow eye, glaucoma suspect group, and normal group (all P < .001). RPC density was strongly correlated with NFL thickness (P < .001) and visual field index (P < .001). CONCLUSIONS: Significant reductions in RPC density were correlated with sites of NFL decrease and visual field loss in glaucoma. Speckle variance OCT-A allows visualization and quantification of RPCs and may therefore be a useful tool for indirectly quantifying and monitoring retinal ganglion cell axonal injury in glaucoma.

Gradient steepness influences the pathfinding decisions of neuronal growth cones in vivo.

Gradients of chemotropic molecules are generally thought to be fundamental for the guidance of neuronal growth cones in the developing embryo. Here we show that the grasshopper-secreted semaphorin Sema 2a is expressed in a gradient during the period of tibial Ti1 pioneer axon pathfinding into the CNS. At two critical Ti1 growth cone choice points, the Sema 2a gradient differs in steepness, whereas the absolute concentration is the same. Although Ti1 growth cones enter and extend up both steep and shallow gradients of Sema 2a, fewer projection errors occur along the steep gradient, suggesting that the steepness of the gradient encodes the critical guidance information into the pathfinding growth cone. In contrast, an increase in the absolute concentration of Sema 2a appears to constrain the Ti1 growth cone size. Using these in vivo gradients, we provide evidence that the Ti1 growth cone detects the Sema 2a gradient by measuring the fractional change in Sema 2a concentration, thereby demonstrating one mechanism that neuronal growth cones may use to detect and read gradients in vivo.

Quantitative Noninvasive Angiography of the Fovea Centralis Using Speckle Variance Optical Coherence Tomography.

PURPOSE: To demonstrate the utility of speckle variance optical coherence tomography (svOCT), a noninvasive angiographic technique, for evaluating the foveal vasculature. METHODS: Twelve normal human eyes were imaged with svOCT (1060-nm, 100-kHz custom-built system) and fluorescein angiography (FA; Topcon TRC-50DX with 5.0 megapixel resolution camera). Manual tracing techniques were used to quantify the foveal vasculature, including foveal avascular zone (FAZ) metrics (area, perimeter, greatest diameter, and lowest diameter). Reproducibility of these measurements was determined. The FAZ was imaged in 25 normal eyes using svOCT and 15 donor eyes using confocal scanning laser microscopy. Retinal capillary plexuses in donor eyes were perfusion-labeled with phalloidin conjugated to Alexa Fluor 546. RESULTS: Speckle variance OCT is able to stratify the foveal circulation into inner and deep capillary plexuses as well as reliably quantify and assess the morphometric dimensions of the human FAZ. Capillary density measurements were significantly greater in svOCT than FA (31.2 ± 1.6% vs. 19.3 ± 1.9% of total tissue area; P < 0.001). Measurements were highly reproducible (all P > 0.366). All FAZ metrics were significantly lower in histology than svOCT (all P < 0.001). CONCLUSIONS: Speckle variance OCT permits precise, reproducible, and noninvasive visualization of the human foveal vasculature. Speckle variance OCT may become an important adjunct in evaluating patients with retinal vascular diseases.