[Normal-pressure glaucoma: a hypothesis of pathogenesis]

Normal pressure glaucoma (NPG) is a heterogeneous pathology of the optic nerve and retina. Besides, primary open-angle glaucoma (POAG) with high pressure belongs equally to the heterogeneous group. The risk factors and pathogenesis stages of NPG and those of POAG do not coincide completely. A considerable number of the NPG cases can be attributed to the glaucoma of pseudo-normal pressure. The individual norm of the intraocular pressure (IOP) does not coincide with the statistical standards. At the same time, POAG with high pressure has, to a more or less extent, the specific features peculiar to NPG. This is especially characteristic of POAG with moderately high IOP. The NPG specific features peculiar to a majority of the examined patients were related with an insufficient cerebral blood circulation caused by occlusive processes in the great and small vessels of the brain, by the nature of the collateral blood circulation and by a dysfunction of the vascular endothelium due to an exhaustion of the cerebral perfusion reserve. The latter is formed mainly at the cost of the vertrebobasilar basin. The mentioned basin supplies blood to the visual tract, as well as to the cerebral centers of the visual analyzer and of the midbrain. Ischemia of the upper corpus bigeminum and of the optic nucleus of the corpus geniculate laterale reduces the formation and supply of neurotrophines (in particular, of BNDF) with the axonal transport to the retinal ganglionic cells, which leads to their apoptosis. Cavernous dystrophy of the optic nerve is a factor preconditioning the occurrence of excavation of the optic nerve head. The mechanic factor related with excavation cannot be ruled out, either. NPG patients often have a relatively large size of the optic nerve disk (OND), therefore, their disk area is equally large. The pressure exerted on the OND is proportional not only to an IOP value, it is also proportional to a disk area. Consequently, provided the IOPs are identical, the mechanical forces exerted on the OND would differ with direct dependence on a disk area. There is every reason to suggest that a considerable share of NPG cases are preconditioned by the cerebrovascular pathology and, therefore, not only the ophthalmologist but also the neurologist must be involved in the diagnostics and treatment of such patients.