Clearance of waste products from the brain is of vital importance. Recent publications suggest a potential clearance mechanism via paravascular channels around blood vessels. Arterial pulsations might provide the driving force for paravascular flow, but its flow pattern remains poorly characterized. In addition, the relationship between paravascular flow around leptomeningeal vessels and penetrating vessels is unclear. In this study, we determined blood flow and diameter pulsations through a thinned-skull cranial window. We observed that microspheres moved preferentially in the paravascular space of arteries rather than in the adjacent subarachnoid space or around veins. Paravascular flow was pulsatile, generated by the cardiac cycle, with net antegrade flow. Confocal imaging showed microspheres distributed along leptomeningeal arteries, while their presence along penetrating arteries was limited to few vessels. These data suggest that paravascular spaces around leptomeningeal arteries form low resistance pathways on the surface of the brain that facilitate cerebrospinal fluid flow.

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The availability of tables with standardized data on the properties of a normal visual visual observer has been a great help in scientific communication. For daily practice these data, going back to the 1920s, still suffice. For basic science they show shortocmings, however. The present paper gives new and extended tables which are intended to be complementary to, rather than to compete with, the old CIE tables.

Recent evidence suggests an extensive exchange of fluid and solutes between the subarachnoid space and the brain interstitium, involving preferential pathways along blood vessels. We studied the anatomical relations between brain vasculature, cerebrospinal fluid compartments, and paravascular spaces in male Wistar rats. A fluorescent tracer was infused into the cisterna magna, without affecting intracranial pressure. Tracer distribution was analyzed using a 3D imaging cryomicrotome, confocal microscopy, and correlative light and electron microscopy. We found a strong 3D colocalization of tracer with major arteries and veins in the subarachnoid space and large cisterns, attributed to relatively large subarachnoid space volumes around the vessels. Confocal imaging confirmed this colocalization and also revealed novel cisternal connections between the subarachnoid space and ventricles. Unlike the vessels in the subarachnoid space, penetrating arteries but not veins were surrounded by tracer. Correlative light and electron microscopy images indicated that this paravascular space was located outside of the endothelial layer in capillaries and just outside of the smooth muscle cells in arteries. In conclusion, the cerebrospinal fluid compartment, consisting of the subarachnoid space, cisterns, ventricles, and para-arteriolar spaces, forms a continuous and extensive network that surrounds and penetrates the rat brain, in which mixing may facilitate exchange between interstitial fluid and cerebrospinal fluid.

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Background: In the 1920s and 1930s, disability glare was a topic of great interest in the Commission Internationale de 1'Éclairage (CIE). The Second World War prevented agreement being reached on a standard to quantify disability glare but the Stiles‐Holladay formula was widely accepted as such. In 1983, CIE started a new effort to develop a CIE standard making use of research data published in the post‐war years. Methods: A committee was formed that agreed that new data and insights justified an extension of the angular domain of a disability glare formula and allowed introduction of an age factor and allowance for ocular pigmentation. Results: Three disability glare equations were formulated, each for an appropriately restricted angular domain. The most general, the CIE General Disability Glare equation, covers the full angular range between 0.1 degrees and 100 degrees but for optometrists the CIE Age‐adjusted Stiles‐Holladay Disability Glare equation, with validity domain between one degree and 30 degrees, will often suffice. Conclusions: Disability glare is due to intraocular scatter and obeys, in the one‐degree to 30‐degree angular domain, albeit with great individual spread, the Age‐adjusted Stiles‐ Holladay equation: (Lveil/Eglare)Age‐adjusted Stiles‐Holladay= 10 (1 + [Age/70]4) 1/θ2. Quantitative examples are given of the manifestation of disability glare, particularly in traffic.

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BackgroundIn the absence of a true lymphatic system in the brain parenchyma, alternative clearance pathways for excess fluid and waste products have been proposed. Suggested mechanisms for clearance implicate a role for brain interstitial and cerebrospinal fluids. However, the proposed direction of flow, the anatomical structures involved, and the driving forces are controversial.MethodsTo trace the distribution of interstitial and cerebrospinal fluid in the brain, and to identify the anatomical structures involved, we infused a mix of fluorescent tracers with different sizes into the cisterna magna or striatum of mouse brains. We subsequently performed confocal fluorescence imaging of horizontal brain sections and made 3D reconstructions of the mouse brain and vasculature.ResultsWe observed a distribution pattern of tracers from the parenchyma to the ventricular system, from where tracers mixed with the cerebrospinal fluid, reached the subarachnoid space, and left the brain via the cribriform plate and the nose. Tracers also entered paravascular spaces around arteries both after injection in the cisterna magna and striatum, but this appeared to be of minor importance.ConclusionThese data suggest a bulk flow of interstitial fluid from the striatum towards the adjacent lateral ventricle. Tracers may enter arterial paravascular spaces from two sides, both through bulk flow from the parenchyma and through mixing of CSF in the subarachnoid space. Disturbances in this transport pathway could influence the drainage of amyloid β and other waste products, which may be relevant for the pathophysiology of Alzheimer’s disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s12987-015-0019-5) contains supplementary material, which is available to authorized users.