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B. Guzek, P. Smolinski, T.R. Friberg; The Mechanism of Radial Optic Neurotomy: Does the Procedure Make Biomechanical Sense? . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4027.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Treating a central retinal vein occlusion (CRVO) by cutting a "fibrous ring" that surrounds the optic nerve head with a small blade (radial optic neurotomy or RON) has been stated to decompress the central retinal vein and is advocated by some as an effective clinical treatment. However, an evaluation of how this procedure could work has not been rigorously performed using biomechanical principles. Methods: We modeled the human eye using finite element analysis making several assumptions regarding the boundary conditions, some of which were based on our previous work in determining the modulus of elasticity of the sclera and choroid. We assumed the following dimensions: inside diameter of the globe –– 18–24 mm; scleral thickness – 1 mm; intraocular pressure – 14–24 mmHg; length of the RON incision –1 mm; optic nerve diameter – 1.4–1.6 mm; scleral modulus elasticity – 2.45Mpa; Poisson’s ratio – 0.45. We also made estimates regarding the interstitial pressure levels within the optic nerve head after CRVO. We studied two models, one in which the globe and nerve were considered as a combined structure, and another where the nerve head itself (but not the sclera) was assumed to be infinitely elastic. Allowing the clinical parameters to vary within realistic ranges, we calculated what the amount of venous decompression expected after a RON procedure, expressed as a percent change in lumen size of the central retinal vein. Results: The percent change in lumen area that the cental retinal vein would undergo after RON was clinically insignificant, varying from 0.2% to 3.4% depending upon the boundary conditions and model used. The increase in volumetric flow rates secondary to such an expansion would be negligible and inadequate to decompress the central retinal vein. Conclusions: The mechanism by which RON has been postulated to produce clinical amelioration of the sequelae of CRVO is not well founded in biomechanical principles. The mechanical effects of RON are likely to be minimal and inconsequential in the clinical setting. Other non–mechanical effects are more likely to play a salient role in the clinical effectiveness of RON or lack thereof.
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