The biomechanical aspect of the pathological optic disc cupping development in glaucoma

PURPOSE: To study the reaction of the soft tissues of the optic nerve head and peripapillary choroidal vessels to compression by the increased IOP. METHODS: The study was performed on 10 healthy volunteers (20 eyes) aged 30 to 62 years (mean age 48 + 10.4 years). An increase in the IOP level was caused the by an extraocular compression. OCT was performed on the Spectralis OCT retinotomograph (Heidelberg Engineering, Germany) before and during the compression. We investigated changes in Bruch's membrane opening diameter, cup width, cup depth and lamina cribrosa depth in response to increased IOP. Also we measured diameter of large peripapillary choroidal and retinal vessels. RESULTS: Changes in almost of all the parameters of ONH except the Bruch's membrane opening diameter and the lamina cribrosa depth manifested in response to an increase of the IOP to 36 mm. It was noted that the cup width increase was more pronounced than the increase in cup depth under the influence of elevated IOP. In cases with IOP elevation to 28 mmHg all parameters of the cup remained unchanged, except for the minimum thickness of the ONH (MRW) in the inferior-temporal and inferiornasal sectors. Acute increased IOP was accompanied by a decrease in diameter of the main vessel of ONH and choroidal vessels at the peripapillary region. CONCLUSION: Obtained results suggest that damage to the nerve fibers in glaucoma may occur not only within the lamina cribrosa, but also in the prelaminar part of the optic nerve head. We introduce a new concept of lateral compressive deformation of the prelaminar part of the optic nerve head under the influence of elevated IOP. This concept can explain some phenomena of the glaucomatous process, which are not completely clear within the traditional paradigm, such as the development of perimetric symptoms towards from the periphery to the center of visual fields with the progression of glaucoma, the appearance of hemorrhages on the edge of the optic nerve, atrophy not only of the neural tissue, but also of the glial and capillary tissues in the prelaminar part of the optic nerve in glaucoma. Further research in this direction can supplement and clarify our understanding of the pathogenesis of glaucoma.

глаукома, ОКТ, головка зрительного нерва, экскавация, решетчатая мембрана, внутриглазное давление, glaucoma, OCT, optic nerve head, optic disc cup, lamina cribrosa, intraocular pressure

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