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The blood–ocular barrier is a barrier created by endothelium of capillaries of the retina and iris, ciliary epithelium and retinal pigment epithelium. [1] It is a physical barrier between the local blood vessels and most parts of the eye itself, and stops many substances including drugs from traveling across it. [2]
Despite the term posterior, this form of damage to the eye's optic nerve due to poor blood flow also includes cases where the cause of inadequate blood flow to the nerve is anterior, as the condition describes a particular mechanism of visual loss as much as the location of damage in the optic nerve.
Other factors can cause glaucoma, known as "secondary glaucoma", including prolonged use of steroids (steroid-induced glaucoma); conditions that severely restrict blood flow to the eye, such as severe diabetic retinopathy and central retinal vein occlusion (neovascular glaucoma); ocular trauma (angle-recession glaucoma); plateau iris; and ...
Brain ischemia is insufficient blood flow to the brain, and can be acute or chronic. Acute ischemic stroke is a neurological emergency typically caused by a blood clot blocking blood flow in a vessel in the brain. [15] Chronic ischemia of the brain may result in a form of dementia called vascular dementia. [16]
The blood retinal barrier has two components: the retinal vascular endothelium and the retinal pigment epithelium. [2] Retinal blood vessels that are similar to cerebral blood vessels maintain the inner blood-ocular barrier. This physiological barrier comprises a single layer of non-fenestrated endothelial cells, which have tight junctions.
Best known is the higher risk of normal tension glaucoma, a disease with an impaired regulation of blood flow in a large number of patients. [9] If glaucomatous damage occurs despite normal eye pressure or if glaucomatous damage is progressive despite normalized intraocular pressure, frequently Flammer syndrome is the cause.
For example, vasoconstriction is a hypothermic preventative in which the blood vessels constrict and blood must move at a higher pressure to actively prevent a hypoxic reaction. ATP is used as a form of energy to increase this pressure to heat the body. Once homeostasis is restored, the blood pressure and ATP production regulates.
Temporary vasospasm leading to decreased blood flow can be a cause of amaurosis fugax. [14] [15] Generally, these episodes are brief, lasting no longer than five minutes, [16] and have been associated with exercise. [10] [17] These vasospastic episodes are not restricted to young and healthy individuals. "Observations suggest that a systemic ...