Pressures in the anterior ciliary arteries, choroidal veins and choriocapillaris

Mäepea, Olav

doi:10.1016/0014-4835(92)90028-q

Cited by 73 publications

(44 citation statements)

References 15 publications

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“…Whether it was a consequence of increased IOP remains unknown. An increase in IOP reduces ocular perfusion pressure 12,13 and therefore reduces blood flow to the eye. On the other hand, retinal blood flow, 14 and to a lesser degree choroidal blood flow, 15 may be autoregulated in response to a decrease in perfusion pressure.…”

Section: Discussionmentioning

confidence: 99%

Influence of infusion volume on the ocular hemodynamic effects of peribulbar anesthesia

Lung

Luksch

Weigert

et al. 2006

Journal of Cataract and Refractive Surgery

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Section: Discussionmentioning

confidence: 99%

Influence of infusion volume on the ocular hemodynamic effects of peribulbar anesthesia

Lung

Luksch

Weigert

et al. 2006

Journal of Cataract and Refractive Surgery

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“…As seen in figure 2, lobules are filled from the centre by an arteriole connected at a right angle relative to the plane of the capillaries and drained by a ring of collecting venules located at the vertices of the lobules and connected in a similar fashion. Each venule drains adjacent lobules so that lobular shapes Fryczkowski (1994) Pressure at the inlets p a 6.75 kPa Mäepa (1992) Pressure at the outlets p v 3.03 kPa Mäepa (1992) TABLE 1. List of physiological parameters characterising the geometry and fluid properties of a choriocapillaris lobule.…”

Section: Geometrymentioning

confidence: 99%

Blood flow in the choriocapillaris

2015

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The choriocapillaris is a capillary bed located in a thin layer adjacent to the outer retina and is part of the oxygen delivery system to the photoreceptors of the eye. The blood flow is approximately planar and is serviced by microvessels, which join the choriocapillaris through inlets perpendicular to its plane. Capillaries are densely organised and separated by avascular septal posts, which direct the blood flow. The capillary bed is composed of a juxtaposition of tessellating vascular units called lobules, which are filled and drained independently from each other. A theoretical analysis of the blood flow in an idealised model of a lobule of the choriocapillaris is developed and studied. Lobules are modelled as tessellating polygonal prisms, where the upper and lower surfaces correspond to planar parallel membranes. The septae are modelled as cylinders randomly distributed between the two membranes. Feeding arterioles and draining venules are modelled as inlets and outlets connecting at the lower surface of the prism perpendicularly to the plane of the lobule. An inlet is placed inside the lobule, while an outlet is placed at each of the vertices. The polygonal prism can be formally subdivided into a set of triangular prisms with one inlet and two outlets, each of them located at one of the vertices. The triangular prisms are taken to be isosceles, and are therefore characterised by a vertex angle ω at the inlet and a span L. The flow is viscously dominated, and is investigated in the lubrication limit, in which the characteristic thickness of the prism is much smaller than the diameter of the cylinders. As a result of the geometry, a stagnation point is located midway between the outlets. A separation streamline joins the inlet and the stagnation point. The pressure drop p and the average fluid particle residence time T are analysed as a function of the angle at the inlet ω and the septae volume fraction Φ. When no cylinders are present (Φ = 0), an analytical expression for the pressure field is calculated by conformal mapping. Close to the triangle walls, the flow is quasi-parallel and characterised by a shorter fluid particle residence time. In the vicinity of the stagnation point, the velocity decreases and the residence time diverges logarithmically with the distance to the stagnation streamline. The minimum in pressure drop corresponds to a maximum in residence time, and is obtained for ω = π/2. Asymptotic expressions for the pressure drop and average residence time are formulated in both the limits ω 1 and π − ω 1. The impact of Φ on the flow is characterised by solving the equations for the flow numerically and using the Darwin drift framework. We show that the pressure drop is approximately proportional to 1 + 2Φ for relatively small Φ, and that T is proportional to 1 − Φ regardless of the void fraction or shape of the septae. In the case Φ = 0, the average † Email address for correspondence: moussa.zouache.10@ucl.ac.uk 38 M. A. Zouache, I. Eames and P. J. Luthert residence time equals the volume of ...

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“…In the eye, IOP exerts an external tissue pressure on many of the ocular vascular beds. Experimental alterations of uveal blood flow demonstrated that the pressure in the large choroidal veins is almost exactly the same as the IOP [19, 20, 21]. Therefore, the perfusion pressure through ocular vascular beds is often defined as the local arterial blood pressure minus the IOP.…”

Section: Discussionmentioning

confidence: 99%

Effect of Carbogen, Oxygen and Intraocular Pressure on Heidelberg Retina Flowmeter Parameter ‘Flow’ Measured at the Papilla

Lietz¹,

Hendrickson²,

Orgül³

et al. 1998

Ophthalmologica

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The aim of the study was to evaluate whether the Heidelberg retina flowmeter (HRF), a new device for retinal and anterior optic nerve blood flow assessment, can gauge, at least semiquantitatively, a known effect such as an increase in optic nerve blood flow by hypercapnia or a decrease in optic nerve blood flow by hyperoxia or high intraocular pressure (IOP). Measurements with the HRF were obtained at the papilla of three groups of 5 young healthy subjects (1) at baseline and after breathing 5% carbogen, (2) at baseline and after breathing 100% oxygen and (3) at baseline and after increasing IOP to 20 and 50 mm Hg. The changes in the value of the HRF parameter ‘flow’ were analyzed by means of a paired Student’s t test. Breathing 100% oxygen for 7 min resulted in a statistically significant decrease of 34.7±2.5% (mean ± SEM) in HR parameter ‘flow’ (p < 0.01) at the papilla. Breathing 5% carbogen for 7 min resulted in a statistically significant increase of 18.3±2.6% in HRF parameter ‘flow’ (p = 0.024). Increasing IOP to 20 mm Hg did not result in a statistically significant change in HRF parameter ‘flow’ (–9.6±7.4%; p = 0.13). Increasing IOP from 20 to 50 mm Hg, however, resulted in a statistically significant decrease of 40.1±6.6% in HRF parameter ‘flow’ (p = 0.003). With the applied stimuli, the HRF parameter ‘flow’ changed in the expected direction, i.e. an increase with hypercapnia and a decrease with hyperoxia or high IOP. The simplicity of use of the HRF instrument suggests that it might be well suited for a non-invasive, at least semiquantitative, assessment of changes in blood flow at the papilla.

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Pressures in the anterior ciliary arteries, choroidal veins and choriocapillaris

Cited by 73 publications

References 15 publications

Influence of infusion volume on the ocular hemodynamic effects of peribulbar anesthesia

Influence of infusion volume on the ocular hemodynamic effects of peribulbar anesthesia

Blood flow in the choriocapillaris

Effect of Carbogen, Oxygen and Intraocular Pressure on Heidelberg Retina Flowmeter Parameter ‘Flow’ Measured at the Papilla

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