الفهرس 
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Abstract
Glaucoma is one of the leading causes of irreversible blindness in the World. It accounts for 13.5% of the global causes of blindness. Glaucoma is increasingly recognized as a condition for which not only elevated intraocular pressure, but also non pressure dependent risk factors are responsible. An underlying vascular etiology has been proposed in the development of glaucomatous optic neuropathy.
Glaucoma can be divided into five main subgroups; congenital glaucoma, primary open angle glaucoma, primary closed angle glaucoma, secondary open angle glaucoma (pigmentary glaucoma, exfoliation syndrome, lens related glaucoma , post-traumatic glaucoma, ghost cell glaucoma and angle recession glaucoma), secondary closed angle glaucoma (e.g. Neovascular glaucoma).
A number of conditions such as congenital glaucoma, angle closure glaucoma, or secondary glaucomas clearly show that increased intraocular pressure is sufficient to cause glaucomatous optic neuropathy. Conversely, the existence of normal tension glaucoma on one hand and patients with ocular hypertension on the other, indicate that other factors might also be involved in the pathogenesis of glaucomatous optic neuropathy, either damaging the nerve directly by poor blood flow to the optic nerve, which leads to death of the cells which carry impulses from the retina to the brain or rendering it more sensitive to intraocular pressure even in the high normal range, and therefore a pressure lower than normal is often necessary to prevent further visual loss.
During the last decade, the presumed etiology of glaucoma has moved from a pure pressure concept to a combined mechanical and vascular theory. Evidence of a localized vascular insufficiency leading to perfusion deficits of ocular structures, including the optic nerve head, the retina, the choroid, and the retrobulbar vessels, is now clear.
Ocular blood flow change can have a structural component, a component related to low perfusion pressure, and additionally, a primary, quite generalized component. Several independent studies demonstrated that ocular blood flow reduction allows a prediction of future progression of damage.
Glaucomatous optic neuropathy comprises of the following mutually dependant basic components: loss of neural tissue, activation of glial cells, tissue remodeling and change of ocular blood flow.
Classical risk factors for atherosclerosis like smoking, dyslipidemia, diabetes, and systemic hypertension were weakly related to glaucomatous optic neuropathy.
Obviously there are a number of factors and mechanisms involved. These factors are most likely interrelated, as in a “complex network”. One of these factors is ocular blood flow and the other, is oxidative stress.
Therefore it was postulated some years ago that glaucomatous optic neuropathy is less linked to a stable reduction of ocular blood flow, but rather to an unstable ocular blood flow, leading to a repeated mild reperfusion injury.
Ocular blood flow is unstable if perfusion pressure fluctuates markedly and exceeds the capacity of autoregulation. Oxidative stress due to unstable ocular blood flow contributes to glaucomatous optic neuropathy. The major cause of a disturbed autoregulation is a primary vascular dysregulation syndrome, which seems often to be due to a vascular endotheliopathy.
The rapid technical progress has provided us a couple of new innovative technologies, which are currently available for the assessment of ocular blood flow. However, only a few of these technologies are currently used in routine patient care and none of these techniques can be regarded as a gold standard for the measurement of ocular blood flow. Nevertheless, the continuous investigation of blood flow parameters has brought us new insights into the physiology of ocular blood flow regulation and the involvement of perfusion abnormalities in ocular disease.
Current ocular imaging technologies measure haemodynamic parameters that may indicate increased circulation, but only with certain assumptions built into the assessment. Each device used to measure ocular blood flow has inherent drawbacks, limiting the conclusions that can be made during their use. Further advances towards creating reliable, reproducible measurements of blood flow, tissue oxygenation, and metabolism in health and disease are needed to improve the understanding of glaucomatous disease.
The imaging technologies most commonly used to investigate ocular blood flow, including color Doppler ultrasound imaging, confocal scanning laser Doppler flowmetry, laser Doppler velocimeter, scanning laser ophthalmoscopic angiography, canon laser blood flowmetry, laser Doppler flowmetry, retinal oximetry , pulsatile ocular blood flow, retinal vessel analyzers, blue field entoptic technique, laser speckle technique and optical Doppler tomography.