Ultrastructural analysis of the lamina cribrosa after radial optic neurotomy.

Radial optic neurotomy (RON) has been proposed for alleviation of the "scleral outlet compartment syndrome" at the level of the lamina cribrosa, which is thought to play a pathoetiologic role in central retinal vein occlusion (CRVO). The aim of this study has been to analyze the ultrastructural alterations of the lamina cribrosa after RON to gain new insights in the underlying pathomechanical factors. Fifteen donor eyes underwent a standardized open-sky-vitrectomy and RON after removal of the anterior eye segment for keratoplasty. Using a microvitreoretinal blade, a radial incision was performed on the nasal hemisphere of the optic nerve head radial to the optic disc and parallel to the nerve fibre layer. The lamina cribrosa and the surrounding scleral ring were then prepared for light microscopy, scanning (SEM) and transmission electron microscopy (TEM). Ultrastructural analysis demonstrated that in 60% (n=9) of the evaluated cases the scleral ring was dissected completely and in 40% (n=6) only partially. The adjacent neuronal tissue to the dissection area showed only minimal injury. The central retinal vessels were not injured in all cases. Only complete incision of the circular ring of collagen fibrils surrounding the lamina cribrosa via RON resulted in effective relaxation of the scleral outlet and was achieved in 60% of all eyes under standardized conditions. In all cases the adjacent tissue showed only minimal injury. The high rate of incomplete dissection of the scleral outlet may be an explanation for the variable outcome seen in different studies on RON.