Ultrastructural Anaysis of the Lamina Cribrosa After Radial Optic Neurotomy

Abstract

Abstract: : Purpose: Radial optic neurotomy (RON) has been proposed to alleviate the "scleral outlet compartment syndrome" at the level of the lamina cribrosa which is discussed to play a pathoetiologic role in central retinal vein occlusion. The aim of this study is to analyze the ultrastructural alterations of the lamina cribrosa after RON to get new insights in the underlying pathomechanical factors. Methods: 15 donor eyes underwent a standardized open–sky–vitrectomy and RON after removal of the anterior eye segment for keratoplastic. Using a microretinal blade a radial incision on the nasal side of the optic nerve head radial to the optic disc and parallel to the nerve fiber layer was performed. The lamina cribrosa was then liberated from the adjacent sclera and prepared for REM, TEM and histological investigations. Results: Ultrastructural analysis demonstrate that in 60% (n=9) of the evaluated cases the scleral ring was dissected completely and in 40% (n=6) partially. The adjacent neuronal tissue showed only minimal injured lesions. The central retinal vessels were not injured in all cases. The lamina cribrosa is surrounded by circular arranged collagen fibrils. Complete dissection of this collagenous ring produces effective relaxation of the scleral outlet and is supported by elastic fibres within the septa of the lamina cribrosa. In cases of incomplete dissection no relaxation was visible indicating ongoing neurovascular compression. Conclusions: Only the complete incision of the circular ring of collagen fibrils surrounding the lamina cribrosa via RON results in effective relaxation of the scleral outlet and was archived in 60% of all eyes under standardized conditions. In all cases the adjacent tissue showed only minimal injured lesions indicating that neuronal and vascular structures preserve nearly their function.

Keywords: retina • optic disc • vascular occlusion/vascular occlusive disease