gms | German Medical Science

Radial optic neurotomy (RON) is a controversial experimental treatment for central retinal vein occlusion. The depth of the RON has not been defined yet. Williamson et al (Br J Ophthalmol 2003) e.g. suggest a depth of 2,5 mm. Complications like an opening of the subarachnoidal space after RON have been described (Samuel et al, Retina 2003). To find out the sufficient depth for RON, this histological study was performed.

19 eye bank eyes without relevant pathology (mean age 64±22 y, anterior-posterior length 23,3±1,1 mm) were worked up histologically in the area of the optic nerve head with serial cuts (interval 5 μm). The distance between the inner surface of the optic disc and the outer limit of the lamina cribrosa was measured. 3 eye bank eyes underwent RON under microscopic control with the Spaide-CRVO-Knife (DORC, Netherlands) after removal of the vitreous and the anterior eye segment. The knife was always introduced nasally 2 mm deep. The cutting depth was assessed histologically.

The distance between the inner surface of the disc and the outer limit of the lamina cribrosa was 1,35±0,3 mm. The experimental RON had histologically verifiable cutting depths of 1,2 mm, 1,72 mm and 1,83 mm.

Based on normal eyes, a cutting depth of 1,4 mm is sufficient to cut through the lamina cribrosa. Eyes with central retinal vein occlusion may also present a papillary edema, which has to be considered. Cutting depths of over 2 mm seem to be too deep and elevate the risk of complications. The histologically detectabel cutting depths of the experimental RON vary a lot with the Spaide-CRVO-knife. It is likely that in the real intraoperative situation the cutting depths might vary even more than that. The development of a knife with a fixed penetration depth would be helpful.