[Radial optic neurotomy for central retinal vein occlusion -- how deep should it be?]

Most of the studies on radial optic neurotomy (RON) have not defined the depth of the incision. Complications following a deeper incision have been described. This histological study was performed to evaluate the required depth for RON.

Serial sections of the area of the optic nerve head were performed in 19 eye bank eyes. The distance between the inner surface of the optic disc and the outer limit of the cribriform plate was measured. Ten additional eye bank eyes underwent 2 mm deep experimental RON using the Spaide CRVO Knife (DORC, Netherlands). The cutting depth was assessed histologically by serial cuts.

The distance between the inner surface of the disc and the outer limit of the cribriform plate measured 1.35+/-0.3 mm (shrinkage-revised value: 1.45 mm). The experimental RON showed cutting depths of 1.53+/-0.3 mm (shrinkage-revised value: 1.65 mm).

Based on normal eyes, a cutting depth of 1.45 mm is sufficient to cut through the cribriform plate. This might change during central retinal vein occlusion because possible papillary edema due to central retinal vein occlusion has to be considered. Even under controlled experimental conditions RON leads to great variation in incision depths. The development of a knife with a fixed penetration depth would be helpful.