Ocular blood flow

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The large vessels of the retina, the arteries appear slightly darker than the veins.

Ocular blood flow describes the blood flow to the eye, especially the blood supply to the anatomical structures of the retina , choroid and optic nerve, which are important for visual perception . The ocular blood flow is important in medicine in two ways: The retina of the eye is the only place in the human body at which blood vessels can be observed without invasive or imaging measures and their function can be quantified or measured. On the other hand, characteristics of the ocular blood flow are of diagnostic significance both for certain eye diseases such as glaucoma and for pathological changes in other organs such as the heart.

anatomy

In principle, the back of the eye is supplied by the bloodstream in two ways. The choroid is the tissue in the body with the most blood supply. From this layer - Latin technical term: choroid - the outer retinal layer, essential for visual perception, is supplied, in which the light-sensitive photoreceptors , the rod cells and cone cells of the retina are located. The other pillar of supply to the retina is the central artery (arteria centralis retinae), which arises from the arteria ophthalmica and, like the draining blood vessel, the central vein (vena centralis retinae) together with the fibers of the optic nerve through the optic disc (papilla) into the eye enters or, in the case of the vein, exits. These two large vessels form a network that encompasses the entire fundus; they branch out into ever smaller arterioles and venules . The retina is the tissue in the human body with the highest oxygen demand - which makes it clear that disturbances in the blood supply are associated with visual disturbances, in the worst case with irreversible damage to the visual organ. A particularly drastic event of this type is an occlusion of the central artery, which usually leads to blindness or severe loss of vision, but pathological changes in the smaller branches of the vessels can also cause pronounced and often permanent impairment of vision. Temporary interruptions to an adequate blood supply can lead to amaurosis fugax .

Diagnosis

The vessels of the retina and, depending on the examination technique, also of the choroid are easily visible to a doctor and can be assessed morphologically. A direct observation is done with the ophthalmoscopy. The predecessor of the ophthalmoscope , the ophthalmoscope invented by Hermann von Helmholtz around 1850, enabled a direct view of the retinal vessels and thus the diagnosis of ocular vascular diseases for the first time. With today's methods, the ocular blood flow can be measured and any disturbances can be detected. The color-coded Doppler sonography is used mainly to assess the blood flow in the retrobulbar vessels, so the arteries and veins that run behind the eyeball. Another technology, Doppler FD-OCT (Optical Coherence Tomography), is suitable for measuring the total blood flow in the retina. A quantitative measurement of the blood flow in the capillaries of the retina and the choroid is also possible with laser Doppler flowmetry. Although angiography of the retinal vessels provides information on the quality of the ocular perfusion and can, for example, detect leaks from the vessels, it does not allow an exact measurement of the blood flow.

Retinal vascular analysis plays a special role in assessing ocular blood flow . While the static vascular analysis documents the condition of the retinal vessels, the dynamic vascular analysis uses an opto-electric flicker light to stimulate and quantify the change in vascular diameter. Conclusions can be drawn about the vascular situation in other body regions and organs from the behavior of the retinal vessels, such as the enlargement of the vessel diameter in response to the light stimulation. The method provides information on vascular damage - for example due to aging processes or metabolic diseases - at an early stage.

Abnormal vascular reactions in the retinal vascular analysis have been documented, among other things, in heart disease and in patients with risks for this (such as obesity).

Clinical significance

Disorders of the ocular blood flow are found in some of the most important eye diseases such as diabetic retinopathy , age- related macular degeneration (AMD) and glaucoma . Particularly in the case of a common variant of the latter, normal pressure glaucoma , a general circulatory problem with what is known as primary vascular dysregulation, i.e. with phases of inadequate blood flow due to regulatory disorders of the blood vessels, has been identified as a major risk factor. The blood flow in the eye is more reduced in normal pressure glaucoma than in high pressure glaucoma (the variant of the disease also known as glaucoma, in which increased intraocular pressure is the most important cause of the disease). Research into this vascular component of normal pressure glaucoma has led to the identification of a phenotype that is now known as Flammer's syndrome . These are people with a generalized dysregulation of the blood vessels who can be more susceptible to certain symptoms and diseases, from cold hands and feet to difficulty falling asleep to tinnitus and migraines. Examining ocular blood flow has become an important step in making a diagnosis.

The importance of changes in ocular blood flow due to dysregulation of the small vessels as a predictor of cardiovascular risks has been demonstrated with the pooled data of two large epidemiological studies, the Beaver Dam Eye Study and the Blue Mountains Eye Study, and has since been confirmed in other publications. Recently, disorders of the ocular blood flow, demonstrated by retinal vascular analysis, have been described as associated with severe kidney damage for the first time. A possible connection between delayed reaction times of the ocular blood flow and Alzheimer's disease is still in the early stages of research.

International research

Research into ocular blood flow has so far mainly been carried out at specialized centers; a large number of scientific publications come from Austria and Switzerland in particular. There, not far from Lucerne on the Rigi , the first international congress specifically dedicated to this topic took place in September 2019.

See also

Individual evidence

  1. ↑ G. Tomita, D. Huang, C. O'Brien, KH Park, T. Nakazawa: Ocular Blood Flow and Visual Function. In: Biomed Res Int. 2015, article 319254, doi: 10.1155 / 2015/319254 .
  2. ↑ A. Mirshahi, N. Feltgen, L. Hansen, LO Hattenbach: vascular occlusions of the retina. An interdisciplinary challenge. In: Deutsches Ärzteblatt . 105 (26), 2008, pp. 474–479, doi: 10.3238 / arztebl.2008.0474 .
  3. ↑ X. Luo, YM Shen, MN Jiang, XF Lou, Y. Shen: Ocular Blood Flow Autoregulation Mechanisms and Methods. In: J Ophthalmol. 2015, article 864871, doi: 10.1155 / 2015/864871 .
  4. ↑ Ronald D. Gerste: Mirror image of the microvasculature. In: Deutsches Ärzteblatt . 115 (48), November 30, 2018, pp. A2234-A2238.
  5. ↑ MR Nägele et al.: Retinal microvascular dysfunction in heart failure. In: European Heart Journal . 39, 2018, pp. 47–56, doi: 10.1093 / eurheartj / ehx565 .
  6. ^ H. Hanssen: Exercise-induced alerations of retinal vessel diameters and cardiovascular risk reduction in obesity. In: Atherosclerosis . 216, 2011, pp. 433-439, doi: 10.1016 / j.atherosclerosis.2011.02.009 .
  7. ↑ K. Konieczka, S. Fränkl: Primary vascular dysregulation and glaucoma (Primary Vascular Dysregulation and Glaucoma). In: Journal of Practical Ophthalmology . 34, 2013, pp. 207-215.
  8. ^ NP Waldmann et al .: The prognostic value of retinal vessel analysis in primary open-angle glaucoma. In: Acta Ophthalmologica . 94 (6), 2016, pp. E474 – e480, doi: 10.1111 / aos.13014 .
  9. ↑ Ronald D. Barley: Eye problems with tinnitus and cold extremities. Flammer's syndrome describes the pathogenesis of a variant of glaucoma in which vascular dysregulations not only dominate in the eye. In: Deutsches Ärzteblatt . February 21, 2014, pp. A308-A309.
  10. ↑ Maneli Mozaffarieh, Josef Flammer: Ocular blood flow and glaucomatous optic neuropathy . Springer, Berlin 2009, ISBN 978-3-540-69442-7 .
  11. ↑ Katarzyna Konieczka, Robert Ritch, Carlo Enrico Traverso, Dong Myung Kim, Michael Scott Kook, Augusto Gallino, Olga Golubnitschaja, Carl Erb, Herbert A. Reitsamer, Teruyo Kida, Natalia Kurysheva, Ke Yao: Flammer syndrome. In: The EPMA Journal. 5, 2014, p. 11, doi: 10.1186 / 1878-5085-5-11 .
  12. ↑ JJ Wang, G. Liew, R. Klein, E. Rochtchina, MD Knudtson, BE Klein, TY Wong, G. Burlutsky, P. Mitchell: Retinal vessel diameter and cardiovascular mortality: pooled data analysis from two older populations. In: Eur Heart J. 28, 2007, pp. 1984–1992, doi: 10.1093 / eurheartj / ehm221 .
  13. ^ J. Flammer, K. Konieczka, RM Bruno, A. Virdis, AJ Flammer, S. Taddei: The eye and the heart. In: Eur Heart J. 34 (17), May 2013, pp. 1270–1278, doi: 10.1093 / eurheartj / eht023 .
  14. ^ MP Nägele, J. Barthelmes, V. Ludovici, S. Cantatore, A. von Eckardstein, F. Enseleit, TF Lüscher, F. Ruschitzka, I. Sudano, AJ Flammer: Retinal microvascular dysfunction in heart failure. In: Eur Heart J. 39 (1), January 2018, pp. 47–56, doi: 10.1093 / eurheartj / ehx565 .
  15. ^ SB Seidelmann et al.: Retinal Vessel Calibers in Predicting Long-Term Cardiovascular Outcomes. In: Circulation . 134, 2016, pp. 1328-1338, doi: 10.1161 / CIRCULATIONAHA.116.023425 .
  16. ^ R. Günthner, H. Hanssen, C. Hauser et al .: Impaired Retinal Vessel Dilation Predicts Mortality in End-Stage Renal Disease. In: Circ Res. April 2019, doi: 10.1161 / CIRCRESAHA.118.314318
  17. ↑ K. Kotliar, C. Hauser, M. Ortner et al.: Altered neurovascular coupling as measured by optical imaging: a biomarker for Alzheimer's disease. In: Scientific Reports . 7, p. 12906, doi: 10.1038 / s41598-017-13349-5 .
  18. ↑ 1st Ocular Blood Flow Summit 2019 , accessed May 16, 2019.

literature