Article
Ultrastructural alterations of the lamina cribrosa after radial optic neurotomy
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Published: | September 22, 2004 |
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Outline
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Objective
The radial optic neurotomy in cases of CVT is a surgical procedure for a pressure relief of neurovascular compression at the site of the lamina cribrosa with a positive influence of blood flow. The aim of this study is to analyze the ultrastructural alterations of preparates after radial optic neurotomy to get new insights in the pathomechanical factors.
Methods
15 donor eyes underwent an open-sky-vitrectomy after removal of the anterior eye segment. The radial optic neurotomy was performed with a microvitreal blade radial to the optic disk and parallel to the nerve fiber pattern to minimize damage to the nerve fibers and blood vessels.The lamina cribrosa was liberated from the adjacent sclera and was prepared for REM, TEM and for histological investigations.
Results
The lamina cribrosa is surrounded by circular arranged collagen fibrils.The radial optic neurotomy was performed through this scleral ring on the nasal side of the disk parallel to the nerve fiber pattern. The adjacent neuronal tissue show minimal injured lesions. The ultrastructural analysis demonstrates that in 60% (n=9) the scleral ring was dissected completely and in 40% (n=6) of the analyzed cases the cirular collagenous ring was dissected partially. The central blood vessels were not injured in all cases. Only complete dissection of the circular collagenous ring produces effective relaxation of the scleral outlet. This mechanism is supported by the elasticity of the elastic fibers within the septa of the lamina cribrosa. In cases of uncomplete dissection of the scleral ring is no relaxation of the lamina cribrosa visible with consecutive relieving neurovascular compression.
Conclusions
Previous investigations to antero- and retrograde axonal transport mechanisms showed alterations of hemodynamic with consecutive damage of retinal axons at the site of the lamina cribrosa. Ischemic swelling of the axons in cases of CVT results in a "scleral outlet compartment syndrome" with interruption of blood flow. Incision of the circular scleral ring of collagen fibrils via radial neurotomy causes a relief of pressure at this location. Our results show that only a complete incision of the circular arranged collagen fibrils causes a relaxation of the penetrating axons and blood vessels. Under standard conditions the adjacent tissue show minimal injured lesions. The neuronal and vascular structures preserve nearly their function.