![]() The loss of this regulatory mechanism can result in ischemia. Vascular length is constant in adult human beings the diameter (radius * 2) remains the main factor controlling blood flow, increasing resistance reduce the blood flow. The mathematical formula describing this resistance is R = (8 × n × l) / (π × r4) with n = blood viscosity, l = vascular length and r = vascular radius. Vascular resistance influences blood flow. For glaucomatous subjects, the difference between venous pressure and intraocular pressure is increased. The ocular arterial pressure has a nycthemeral variation, higher at night when lying down. The intraocular arterial pressure is inaccessible directly, so we use the brachial mean arterial pressure (MAP): MAP = DBP + 1/3 (SBP − DBP), with SBP = systolic blood pressure and DBP = diastolic blood pressure. ![]() Another equation is OPP = 2/3 mean arterial blood pressure – IOP. Ocular perfusion pressure (OPP) can be defined by the difference between arterial pressure (AP) and venous pressure (VP): OPP = AP –VP. ![]() The hypoperfusion and the loss of vascular autoregulation result in ischemia and oxidative stress. The second theory is the vascular theory : decreased ocular blood flow and optic nerve perfusion result in RGC apoptosis, secondary to mechanical effects such as IOP or systemic effects such as cardiovascular risk factors. Nevertheless, this theory is insufficient to explain glaucoma because many glaucoma patients progress with normal IOP, and many patients have high IOP without developing glaucoma. Many studies have shown IOP as a risk factor for developing glaucoma and its progression. The lamina cribrosa becomes thinner and deformed, increasing the Cup / Disc ratio, impeding axoplasmic flow within the optic nerve fibers, ending with RGC apoptosis. The mechanical theory explains apoptosis by disruption of the axonal transport of retinal ganglion cells (RGC) at the lamina cribrosa secondary to relatively elevated intraocular pressure (IOP). The pathophysiology of glaucoma is not yet fully understood, but two theories try to explain the apoptosis of retinal ganglion cells. Vascular and Mechanical theories of glaucoma However, before going into the details of OCTA, we should first focus on the vascular theory of glaucoma and vascularization of the optic nerve. OCT Angiography is a recent, non-invasive and fast technology that allows the visualization of retinal and papillary vessels, which can help to diagnose glaucoma. Ĭonsequently, there is a need to develop technology to help diagnose glaucoma. Despite this, approximately 50% of glaucomas are undiagnosed. The diagnosis depends on the clinical examination (optic disc, retinal fibers, gonioscopy, intraocular pressure) and complementary exams (visual fields and optical coherence tomography, OCT). Therefore, the diagnosis is critical to prevent blindness. It is the second leading cause of blindness, which is unfortunately irreversible. Glaucoma is an optic neuropathy with typical changes in the optic nerve head, retinal nerve fiber layer, and visual fields. Studies have shown that OCTA detects decreased vascular density in glaucoma. Optical Coherence Tomography Angiography (OCTA) is a recent, non-invasive and fast technology that allows the visualization of retinal and papillary vessels. Fifty percent of glaucomas are undiagnosed consequently, we should develop new technologies to aid in glaucoma diagnosis. Glaucoma is the first cause of irreversible blindness in the world. 4.6 Two OCTA devices with the same patient.4.5 OCTA VD increase after glaucoma surgery.4.4 Advanced asymmetric glaucoma and myopia.4.3 Glaucomatous versus healthy patient – whole-image macular OCTA.4.2 Glaucomatous patient - whole-image optic nerve OCTA.4 Clinical cases and images of OCTA and glaucoma.3.9.4 Leber hereditary optic neuropathy.3.9.3 Anterior ischemic optic neuropathy.3.9 OCTA and systemic and neuro-ophthalmological diseases.3.1 Historical considerations and functioning principles of OCT and OCTA.2.2 Anatomy - Vascularization of the optic nerve.2.1 Vascular and Mechanical theories of glaucoma. ![]()
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