Nerve Fiber Bundles Research Articles

A model of ganglion axon pathways accounts for percepts elicited by retinal implants

Degenerative retinal diseases such as retinitis pigmentosa and macular degeneration cause irreversible vision loss in more than 10 million people worldwide. Retinal prostheses, now implanted in over 250 patients worldwide, electrically stimulate surviving cells in order to evoke neuronal responses that are interpreted by the brain as visual percepts (‘phosphenes’). However, instead of seeing focal spots of light, current implant users perceive highly distorted phosphenes that vary in shape both across subjects and electrodes. We characterized these distortions by asking users of the Argus retinal prosthesis system (Second Sight Medical Products Inc.) to draw electrically elicited percepts on a touchscreen. Using ophthalmic fundus imaging and computational modeling, we show that elicited percepts can be accurately predicted by the topographic organization of optic nerve fiber bundles in each subject’s retina, successfully replicating visual percepts ranging from ‘blobs’ to oriented ‘streaks’ and ‘wedges’ depending on the retinal location of the stimulating electrode. This provides the first evidence that activation of passing axon fibers accounts for the rich repertoire of phosphene shape commonly reported in psychophysical experiments, which can severely distort the quality of the generated visual experience. Overall our findings argue for more detailed modeling of biological detail across neural engineering applications.

Discordance of Disc-Fovea Raphe Angles Determined by Optical Coherence Tomography and MP-3 Microperimetry in Eyes With a Glaucomatous Hemifield Defect.

The purpose of this study was to evaluate the concordance of a temporal raphe architecture estimated using optical coherence tomography (OCT) and MP-3 microperimetry. We enrolled 25 eyes with either an upper or lower glaucomatous hemifield defect, as detected on the Humphrey visual field 30-2 test. A structural temporal raphe was extrapolated from visible end points of retinal nerve fiber bundles present in a perimetrically normal hemiretina on an en face Spectralis OCT image. A functional temporal raphe was drawn as a line from the fovea to the border of at least a 10-dB difference in sensitivity, at vertically adjacent test points, with at least three consecutive pairs among 25 test points placed at 8° to 18° from the fovea (2° intervals) on the MP-3. An angle determined by the optic disc center, the fovea, and the temporal raphe line (the DFR angle) was calculated. Correlations and agreement of the OCT- and MP-3-derived DFR angles and factors affecting discordance of the two estimates were evaluated. Despite no significant demographic differences, the functional DFR angle (mean ± SD, 171.8° ± 3.5°) was significantly larger than that of the structural DFR angle (166.5° ± 3.2°) in 14 eyes with upper hemifield defects and vice versa in 11 eyes with lower hemifield defects (163.4° ± 3.0° vs. 170.5° ± 3.2°). The mean deviation was significantly associated with the functional and structural DFR angle difference in eyes with only upper hemifield defects. The structural temporal raphe was more deviated to the perimetrically normal hemiretina side than to the functional temporal raphe, thereby suggesting that a structural change may precede a functional loss.

Developmental localization of syntaxin 1 and synaptosomal‐associated protein 25 in rat palate

IntroductionThe palate, which plays an important role in oral cavity function, including the mastication and swallowing of food, obviously differs structurally with feeding habits. Nevertheless, the palate is considered the most common location of both benign and malignant minor salivary gland tumors. Soluble N‐ethylmaleimide‐sensitive fusion protein attachment protein receptor (SNARE) proteins are important in the control of tumorigenesis through the regulation of multiple signaling and transportation pathways. However, the developmental distribution of SNARE proteins on the palatal structures has been scarcely reported. Therefore, this study aimed to investigate SNARE proteins, syntaxin‐1, synaptosomal‐associated protein of 25 kDa (SNAP‐25) during the development of rat palates.Materials and MethodsImmunohistochemistry for protein gene product 9.5 (PGP 9.5), a pan‐neuronal marker, syntaxin‐1 and SNAP‐25 was performed on frozen sections of rat palatal tissues at different stages.ResultsPGP 9.5 immunoreactive fibers (IRF) were present in developing palate. They were observed along the palatal sub‐epithelial layer and the underlying connective tissues in association with developing acini, ducts, blood vessels. Nerve fibers containing syntaxin‐1 and SNAP‐25 showed similar distribution to PGP 9.5 and thick bundles of nerve fibers were observed with smooth muscles and varicoses. With maturation after postnatal day 7 (PN7), thin nerve fibers containing PGP 9.5 and SNAP‐25, but less syntaxin‐1, were detected penetrating into the epithelium, reaching beneath the cornified layer. They ramified out from subepithelial thick bundles into connective tissues until encircling the secretory units observed (PN21). In adults, the number of syntaxin‐1‐IRF was low in comparison with SNAP‐25 and PGP 5 fibers.ConclusionThe findings indicated the importance of SNARE proteins during the maturation of the palatal tissues.Support or Funding InformationNoneThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Comparative study of extracellular recording methods for analysis of afferent sensory information: Empirical modeling, data analysis and interpretation

BackgroundPhysiological studies of sensorial systems often require the acquisition and processing of data extracted from their multiple components to evaluate how the neural information changes in relation to the environment changes. In this work, a comparative study about methodological aspects of two electrophysiological approaches is described. New methodExtracellular recordings from deep vibrissal nerves were obtained by using a customized microelectrode Utah array during passive mechanical stimulation of rat´s whiskers. These recordings were compared with those obtained with bipolar electrodes. We also propose here a simplified empirical model of the electrophysiological activity obtained from a bundle of myelinated nerve fibers. ResultsThe peripheral activity of the vibrissal system was characterized through the temporal and spectral features obtained with both recording methods. The empirical model not only allows the correlation between anatomical structures and functional features, but also allows to predict changes in the CAPs morphology when the arrangement and the geometry of the electrodes changes. Comparison with existing method(s)This study compares two extracellular recording methods based on analysis techniques, empirical modeling and data processing of vibrissal sensory information. ConclusionsThis comparative study reveals a close relationship between the electrophysiological techniques and the processing methods necessary to extract sensory information. This relationship is the result of maximizing the extraction of information from recordings of sensory activity.

Formulation and Efficient Computation of l1 - and Smoothness Penalized Estimates for Microstructure-Informed Tractography.

Fiber tractography based on diffusion-weighted magnetic resonance imaging is to date the only method for the three-dimensional visualization of nerve fiber bundles in the living human brain noninvasively. However, various existing methods suffer from reconstructing anatomically implausible fiber tracks due to exclusive local treatment of the input data. A method that seeks to filter out invalid tracks in a postprocessing step by solving a convex optimization problem with l1 -norm regularization was recently introduced in the work by Daducci et al. In this paper, we derive an improved version of this method by adding Sobolev-norm regularization terms. Furthermore, we present a robust and efficient strategy using the alternating direction method of multipliers and dimension reduction using truncated singular value decomposition to solve the resulting optimization problem. The qualitative results show the applicability of the algorithm to large in vivo data sets. The quantitative results and numerical experiments for diffusion phantom data with known ground truth show the benefits of the proposed method.

Histoarchitectural Changes in the Stromal Tissue of Udder of Small Ruminants

In both ewes and she-goats, the mammary gland was covered from without inwards by skin and fibroelastic capsule. Udder skin made up of epidermis and dermis. Epidermis lined by stratified squamous keratinised epithelium. Dermis composed of dense irregular connective tissue with numerous sweat glands, sebaceous glands, hair follicles, and nerve fibres. Statistically no difference was observed in capsule thickness between lactating and non-lactating groups in Madras Red ewes and Boer local she-goats. The amount of stromal tissue varied between lactating and non-lactating animals. It was found to be more in non-lactating animals. The interalveolar septae were composed of collagen, elastic and reticular fibres, fibroblast, smooth muscle fibres, fat cells and nerve fibre bundles. Bundles of thick, dense connective tissue made of collagen, elastic and reticular fibres constituted the interlobar septae. Highly significant difference was observed in the thickness of interalveolar and interlobular septa between lactating and non-lactating groups in both ewes and she-goats.

Effect of exosomes from adipose-derived stem cells on peripheral nerve regeneration

To investigate the effects of exosomes from adipose-derived stem cells (ADSCs) on peripheral nerve regeneration, and to find a new treatment for peripheral nerve injury. Thirty-six adult Sprague Dawley (SD) rats (male or female, weighing 220-240 g) were randomly divided into 3 groups ( n=12). Group A was the control group; group B was sciatic nerve injury group; group C was sciatic nerve injury combined with exosomes from ADSCs treatment group. The sciatic nerve was only exposed without injury in group A, and the sciatic nerve crush injury model was prepared in groups B and C. The SD rats in groups A and B were injected with PBS solution of 200 μL via tail veins; the SD rats in group C were injected with pure PBS solution of 200 μL containing 100 μg exosomes from ADSCs, once a week and injected for 12 weeks. At 1 week after the end of the injection, the rats were killed and the sciatic nerves were taken at the part of injury. The sciatic nerve fiber bundles were observed by HE staining; the SCs apoptosis of the sciatic nerve tissue were detected by TUNEL staining; the ultrastructure and SCs autophagy of the sciatic nerve were observed by transmission electron microscope. Gross observation showed that there was no obvious abnormality in the injured limbs of group A, but there were the injured limbs paralysis and muscle atrophy in groups B and C, and the degree of paralysis and muscle atrophy in group C were lighter than those in group B. HE staining showed that the perineurium of group A was regular; the perineurium of group B was irregular, and there were a lot of cell-free structures and tissue fragments in group B; the perineurium of group C was more complete, and significantly well than that of group B. TUNEL staining showed that the SCs apoptosis was significantly increased in groups B and C than in group A, in group B than in group C ( P<0.01). Transmission electron microscope observation showed that the SCs autophagosomes in groups B and C were significantly increased than those in group A, but the autophagosomes in group C were significantly lower than those in group B. The exosomes from ADSCs can promote the peripheral nerve regeneration. The mechanism may be related to reducing SCs apoptosis, inhibiting SCs autophagy, and reducing nerve Wallerian degeneration.

Dual Convergence of Facial Nerve Branches Innervating Whisker Pad in Rats.

The precise anatomy of the facial nerve branches innervating rat whisker pad and the distribution of their corresponding motor neurons in facial nucleus area were investigated. The extratemporal facial nerves of 6 rats were anatomically observed under a surgical microscope, and then the nerve specimens of facial nerve branches at 7 anatomical sites were taken and examined for the axons and myelin sheath using Luxol fast blue staining. The distribution of facial motor neurons innervating the facial branches was observed in 12 rats by retrograde labelling. The distal pes, a fusing architecture of the buccal and marginal mandibular branches, was found to furcate into superior, middle and inferior branches to innervate whisker pad. Histologically, the myelin sheath of each branch was morphologically consistent, and the nerve fiber bundles of facial nerve branches became increasingly thinner and scattered, particularly after crossing the distal pes site and innervating the whisker pad. The facial motor neurons innervating the buccal and marginal mandibular branches were clearly distributed in similar regions in facial nucleus. This study confirmed the highly spatial synergy between the buccal and marginal mandibular branches innervating the whisker pad from extratemporal anatomy and distribution of facial motor neurons.

Microtubule Imaging Reveals Cytoskeletal Deficit Predisposing the Retinal Ganglion Cell Axons to Atrophy in DBA/2J.

PurposeGlaucoma is characterized by progressive loss of the retinal ganglion cells (RGCs) and their axons. Here we test an outstanding notion that microtubules (MTs) within RGC axons degrade before the loss of morphology (“MT hypothesis”).MethodsThe integrity of axonal MTs was interrogated by intrinsic second-harmonic generation (SHG) microscopy. Using DBA/2J mice as a model of glaucoma and DBA/2J-Gpnmb+ as a nonglaucomatous control, the relationship between MT disruption and morphology was quantitatively examined as a function of age and sex in the fresh retinal wholemounts.ResultsThe mean SHG density (i.e., the mean SHG intensity per thickness) was significantly lower in DBA/2J than in DBA/2J-Gpnmb+ and also depended on sex and age. The loss of SHG density, indicating MT disruption within intact RGC axons, occurred in a sectorial manner near the loss of the retinal nerve fiber bundles. The decay rate of SHG density was approximately 97% higher than that of thickness.ConclusionsCollectively, the results indicate that the breakdown of MTs is pathology of glaucoma and likely a precursor of morphological atrophy. Based on a new finding that SHG density is highly variable and spatially discrete, a new model of RGC degeneration is proposed. This study validates SHG retinal imaging for elucidating the role and mechanism of MT deficiency in the course of glaucoma pathogenesis.

Loss of Tbx3 in murine neural crest reduces enteric glia and causes cleft palate, but does not influence heart development or bowel transit

Transcription factors that coordinate migration, differentiation or proliferation of enteric nervous system (ENS) precursors are not well defined. To identify novel transcriptional regulators of ENS development, we performed microarray analysis at embryonic day (E) 17.5 and identified many genes that were enriched in the ENS compared to other bowel cells. We decided to investigate the T-box transcription factor Tbx3, which is prominently expressed in developing and mature ENS. Haploinsufficiency for TBX3 causes ulnar-mammary syndrome (UMS) in humans, a multi-organ system disorder. TBX3 also regulates several genes known to be important for ENS development. To test the hypothesis that Tbx3 is important for ENS development or function, we inactivated Tbx3 in all neural crest derivatives, including ENS progenitors using Wnt1-Cre and a floxed Tbx3 allele. Tbx3 fl/fl; Wnt1-Cre conditional mutant mice die shortly after birth with cleft palate and difficulty feeding. The ENS of mutants was well-organized with a normal density of enteric neurons and nerve fiber bundles, but small bowel glial cell density was reduced. Despite this, bowel motility appeared normal. Furthermore, although Tbx3 is expressed in cardiac neural crest, Tbx3 fl/fl; Wnt1-Cre mice had structurally normal hearts. Thus, loss of Tbx3 within neural crest has selective effects on Tbx3-expressing neural crest derivatives.

Trans-retinal cellular imaging with multimodal adaptive optics.

Adaptive optics (AO), when coupled to different imaging modalities, has enabled resolution of various cell types across the entire retinal depth in the living human eye. Extraction of information from retinal cells is optimal when their optical properties, structure, and physiology are matched to the unique capabilities of each imaging modality. Despite the earlier success of multimodal AO (mAO) approaches, the full capabilities of the individual imaging modalities were often diminished rather than enhanced when integrated into multimodal platforms. Furthermore, many mAO designs added unnecessary complexity, making clinical translation difficult. In this study, we present a novel mAO system that combines two complementary approaches, scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT), in one instrument using a simplified optical design, flexible alternation of scanning modes, and independent focus control. The mAO system imaging performance was demonstrated by visualization of cells in their mosaic arrangement across the full depth of the retina in three human subjects, including microglia, nerve fiber bundles, retinal ganglion cells and axons, and capillaries in the inner retina and foveal cones, peripheral rods, and retinal pigment epithelial cells in the outer retina. Multimodal AO is a powerful tool to capture the most complete picture of retinal health.

Visualization of the Membranous Labyrinth and Nerve Fiber Pathways in Human and Animal Inner Ears Using MicroCT Imaging

Design and implantation of bionic implants for restoring impaired hair cell function relies on accurate knowledge about the microanatomy and nerve fiber pathways of the human inner ear and its variation. Non-destructive isotropic imaging of soft tissues of the inner ear with lab-based microscopic X-ray computed tomography (microCT) offers high resolution but requires contrast enhancement using compounds with high X-ray attenuation. We evaluated different contrast enhancement techniques in mice, cat, and human temporal bones to differentially visualize the membranous labyrinth, sensory epithelia, and their innervating nerves together with the facial nerve and middle ear. Lugol’s iodine potassium iodine (I2KI) gave high soft tissue contrast in ossified specimens but failed to provide unambiguous identification of smaller nerve fiber bundles inside small bony canals. Fixation or post-fixation with osmium tetroxide followed by decalcification in EDTA provided superior contrast for nerve fibers and membranous structures. We processed 50 human temporal bones and acquired microCT scans with 15 μm voxel size. Subsequently we segmented sensorineural structures and the endolymphatic compartment for 3D representations to serve for morphometric variation analysis. We tested higher resolution image acquisition down to 3.0 μm voxel size in human and 0.5 μm in mice, which provided a unique level of detail and enabled us to visualize single neurons and hair cells in the mouse inner ear, which could offer an alternative quantitative analysis of cell numbers in smaller animals. Bigger ossified human temporal bones comprising the middle ear and mastoid bone can be contrasted with I2KI and imaged in toto at 25 μm voxel size. These data are suitable for surgical planning for electrode prototype placements. A preliminary assessment of geometric changes through tissue processing resulted in 1.6% volume increase caused during decalcification by EDTA and 0.5% volume increase caused by partial dehydration to 70% ethanol, which proved to be the best mounting medium for microCT image acquisition.

Retinal nerve fiber bundle trajectories in Chinese myopic eyes: Comparison with a Caucasian based mathematical model

Previously we developed a mathematical model for describing the retinal nerve fiber bundle (RNFB) trajectories in the human retina. The model was based on Caucasian eyes that were not selected regarding refraction. The aim of this study was to determine the characteristics of the RNFB trajectories in Chinese myopic eyes. We collected high quality red free fundus images from 80 eyes of 80 Chinese myopic subjects (median [interquartile range/range] refraction −3.9 [-6.0 to −2.5/-10 to −1] D). We traced all visible RNFBs (n = 1460) and evaluated their trajectories using the previously published mathematical model. In the superior-temporal region, the RNFB trajectories of the Chinese myopic eyes were similar to that of the Caucasian eyes (86% of trajectories within the 95% central range of the Caucasian model). In the inferior-temporal region, the trajectories of the Chinese low to moderate myopic eyes were also similar to that of the Caucasian eyes (85%); trajectories of the high myopic eyes (spherical equivalent beyond −6.00 D) were clearly less curved (75%). Associations between individual deviations from the model and axial length, retinal vessel course, and optic disc anatomy were studied with multiple linear regression analysis. In the superior-temporal region, the trajectories were associated with retinal vessel course (P = 0.008) and optic disc size (P = 0.016). In the inferior-temporal region, there was a significant association with axial length (P < 0.001), retinal vessel course (P = 0.006), and disc torsion (P = 0.009).

A Pilot Study On The Novel Non-Invasive Nerve-Holder With Negative-Pressure Suctions.

In performing neurosurgical operation on peripheral nervous system, the most important first step is to robustly hold the target nerve, since the nerve-holding stability and reliability significantly affect the result of surgical operation. However it is not straightforward to robustly hold peripheral nerve during the surgical operation, because the peripheral nerve is too flexible and slippery. In this study, we design a novel peripheral nerve-holder that can be used for the neurosurgical operation. Considering the anatomical characteristics of the peripheral nerve that small bundles of nerve fibers (i.e., fascicles) are structured inside the outermost layer of the nerve bundle (i.e., epineurium), we aim to develop a non-clamping and non-invasive type nerve-holder to protect the nerve fibers. For the aim, the negative-pressure suction method is applied to the proposed holder. And, in order to hold the nerve more robustly, micro-bump structure is fabricated on the suction surface contacting with the nerve. This paper introduces the concept, working principle, characteristics, and in-vitro experimental results on feasibility evaluation of the proposed holder.

Dependence of Scan Parameters on Nerve Fiber Crossing Depiction in Diffusion Spectrum Imaging in Clinical Practice.

The objective of this study was to show the effect of the number of sampling points (NS) and the maximum b value (bmax) on fiber crossing detection in diffusion spectrum imaging (DSI) in clinical practice. We performed 3-Tesla DSI in which we changed the NS (62-258) while keeping bmax at 8000 s/mm and in which we changed the bmax (4000-8000 s/mm) while keeping the NS at 129. The superior longitudinal fasciculus volume and the proportion of nerve voxels in which at least 2 (Rcr2) or 3 (Rcr3) nerve fiber bundles crossed were calculated. When bmax was set to 8000 s/mm, mean Rcr2 and Rcr3 values and superior longitudinal fasciculus volumes significantly increased with higher NSs, but they did not significantly change when we varied bmax with 129 NS. Depiction sensitivity of nerve fiber crossing in DSI improves at higher NS and bmax settings, but a bmax insensitivity appears at an intermediate NS such as 129.

Age is reflected in the Fractal Dimensionality of MRI Diffusion Based Tractography

Fractal analysis is a widely used tool to analyze the geometrical complexity of biological structures. The geometry of natural objects such as plants, clouds, cellular structures, blood vessel, and many others cannot be described sufficiently with Euclidian geometric properties, but can be represented by a parameter called the fractal dimension. Here we show that a specific estimate of fractal dimension, the correlation dimension, is able to describe changes in the structural complexity of the human brain, based on data from magnetic resonance diffusion imaging. White matter nerve fiber bundles, represented by tractograms, were analyzed with regards to geometrical complexity, using fractal geometry. The well-known age-related change of white matter tissue was used to verify changes by means of fractal dimension. Structural changes in the brain were successfully be observed and quantified by fractal dimension and compared with changes in fractional anisotropy.

Novel Technique for Quantifying Retinal Nerve Fiber Bundle Abnormality in the Temporal Raphe.

SIGNIFICANCEGlaucomatous nasal visual field abnormalities correspond to damage in the temporal raphe—where individual nerve bundles can be visualized. The ability to quantify structural abnormality in the raphe, with a clinically applicable protocol, sets the stage for investigating the raphe as a potential site for assessing early glaucoma.PURPOSETo develop a clinically applicable imaging and analysis technique for identifying retinal nerve fiber bundle abnormalities in the temporal raphe.METHODSSpectralis optical coherence tomography scans customized for the temporal raphe were gathered from 30 younger controls, 30 older controls, and 29 patients with glaucoma. An analysis technique was developed based on the reflectance of the nerve fiber bundles. The technique was first developed in the younger controls, and then applied to the older controls to generate normative data for quantifying nerve fiber bundle reflectance abnormalities in the patients with glaucoma. Matrix perimetric data were gathered in the patients with glaucoma to evaluate the reflectance technique’s findings. Reflectance abnormality in the patients was defined when the fraction of enface area showing reflectance abnormality was greater than the 95th percentile estimated from controls. Spearman’s rho was used to quantify the relation between the total deviation at the perimetric testing locations and the fraction of corresponding enface area showing reflectance abnormality.RESULTSTwenty-five of the 29 patients had reflectance abnormalities. Eight of these had mild to no perimetric mean deviation abnormality. Similar results were found when perimetric total deviations were compared to reflectance abnormalities in the corresponding enface locations. Spearman’s rho comparing the total deviations to reflectance abnormalities found rs(174) = −0.72, P < .001.CONCLUSIONSThe technique typically identified reflectance abnormality when perimetric abnormality was present. It also identified reflectance abnormalities even when perimetric abnormality was mild or absent. The findings support the potential of raphe imaging in detecting early glaucomatous damage.

Retinal putative glial alterations: implication for glaucoma care.

PurposeGliosis‐like retinal alterations, presumed to be activated retinal astrocytes and Müller cells (ARAM), have been reported to occur frequently in patients with glaucoma but rarely in controls. We investigated the association between glaucomatous abnormality and the presence, the extent of retinal region, and the spatial distribution, of hyperreflective retinal alterations on optical coherence tomography (OCT) en‐face images, presumed to be ARAM.MethodsFindings of hyperreflective structures, presumed to be ARAM, in the central retinal ±24 degrees of OCT en‐face images (acquired with the SPECTRALIS® OCT) were compared between 35 younger controls, 42 older controls and 38 patients with glaucoma. Presumed ARAM was defined as reflective structures on the en‐face images other than retinal vasculature and retinal nerve fibre bundles. Chi‐square tests were used to compare the proportion of younger controls vs older controls with presumed ARAM to investigate the effect of ageing, and the proportion of patients vs age‐similar older controls with presumed ARAM to investigate the effect of disease. We also investigated the effect of glaucoma on the retinal area with presumed ARAM when it was present; we used an analysis of covariance (ancova) to compare the retinal area with hyperreflectivity in patients vs controls, adjusting for the effects of age and axial length.ResultsThe mean (S.D.) age of the younger controls, older controls, and patients with glaucoma was 26 (3), 62 (10) and 69 (8) years, respectively. The median (25th quartile, 75th quartile) of the retinal region with the hyperreflective structures, presumed to be ARAM, was zero (0,0), 1 (0,6), and 11 (0,43) degrees square in the younger controls, older controls and patients with glaucoma respectively. The chi‐square test investigating the effect of ageing found χ2(1, N = 77) = 24.8, p < 0.001, and that investigating the effect of disease found χ2(1, N = 80) = 2.3, p = 0.1. The ancova found F(1, 46) = 10.32, P = 0.02.ConclusionsThere was an effect of ageing on the presence of the hyperreflective structures, presumed to be ARAM, on OCT images. Compared to the presence of hyperreflective structures, the extent of retinal region with the hyperreflective structures has a greater potential of being an indicator of glaucomatous degeneration. Further study is needed to investigate the nature of the relation between glaucomatous abnormality and the extent of the retina with the hyperreflective structures, presumed to be ARAM.

Wide-Field OCT Angiography Investigation of the Relationship Between Radial Peripapillary Capillary Plexus Density and Nerve Fiber Layer Thickness.

PurposeTo characterize the density and distribution of the radial peripapillary capillary plexus (RPCP) and its relationship with retinal nerve fiber layer (NFL) thickness in healthy subjects.MethodsUsing spectral-domain optical coherence tomography (OCT), split-spectrum amplitude decorrelation angiography algorithm and automated montaging, wide-field OCT angiography (OCTA) was used to measure the RPCP capillary density (CD) and NFL thickness. Polar sector-average CD and thickness maps were also created on each eye.ResultsWide-field OCTA (8 × 8 mm) in 10 healthy eyes from 10 subjects demonstrated the distribution of the RPCP throughout the posterior pole. RPCP-CD decreases with distance from the disc, but along the arcuate nerve fiber bundles relatively dense (> half maximum density) RPCP extends more than 5 mm from the disc and includes regions superior to and inferior to the macula. The RPCP-CD and NFL thickness are highly correlated (R2 = 0.85, P < 0.001) and fit well with a nonlinear stacked-layer model. The model fit suggests that the RPCP is present when the NFL is thicker than 17.9 μm and reaches a ceiling area density of 84% and that the RPCP has an apparent volume density of 19% at the current instrument transverse resolution. This indicates that capillary overlap can be expected to occur when NFL thickness reaches 40 μm.ConclusionsThe wide distribution of dense overlapping RPCP suggests that wider (up to 8 mm vertical and 7 mm horizontal) OCTA scans may be better investigate capillary loss in the early stages of glaucoma or other optic neuropathies.

Subject specific angular waist of the optic nerve head nerve fiber layer allows follow up detection of local nerve fiber bundle loss

PurposeTo clarify if frontal plane angular Pigment epithelium central limit‐ Inner limit of the retina Minimal Distance (PIMD) measured with OCT has enough specific angular structure for detection of change of specific angular segments of PIMD over time within glaucoma subjects.MethodsA Topcon OCT‐2000 was used for capture of the 3D representations of the ONH. from one eye of each of totally 13 subjects with early stage primary open angle glaucoma. Altogether, 3 volumes were captured at two occasions within 3 months. PIMD was semi‐automatically segmented in each volume in 500 equally spaced angular segments distributed over 2Pi in the frontal plane.ResultsPlots of the angular distribution of PIMD for all subject revealed specific low angular frequency overlaid with higher intermediate angular frequencies specific for each subject. High angular frequencies appeared similar for all subjects. A fast Fourier transform of the angular PIMD revealed a high to low frequency content ratio, 0.12, consistent for all segmentations of PIMD‐2Pi. The rotational displacment of angular PIMD in the frontal plane among segmentations, volumes and occasions was determined with cross‐correlation. Then, all PIMD‐2Pi were phase adjusted over segments, volumes and occasions. Finally, the rotation of PIMD‐2Pi was adjusted to a standard rotation. This allows comparison of angular segments of PIMD‐2Pi between visits. The magnitude of different sources of variation were estimated with analysis of variance.ConclusionsAngular correction in the frontal plane of recordings of angular PIMD of the ONH allows comparison of angular segments of PIMD‐2Pi. This substantially increases the resolution of of an angular segment of PIMD. The resulting precision suggest that detection of an angular segment of PIMD is associated with better resolution than Humphrey visual field MD.