Study of Radial Optic Neurotomy Outcomes in Normal Rat Eyes

D. DORFMAN; J. CROXATTO; N. DE ZAVALÍA; R. E. ROSENSTEIN; N. BELFORTE

Fort Lauderdale, USA

Congreso; Association for Research in Vision and Ophthalmology (ARVO); 2010

Purpose:Radial optic neurotomy (RON) consists in the surgical dissection of the lamina cribrosa transvitreally via a radial incision on the nasal side of the optic nerve. RON was proposed as a surgical treatment for central retinal vein occlusion (CRVO). Although improvements in visual acuity by RON in patients with CRVO have been confirmed by several investigators, it is still controversial whether the incision of the scleral outlet is a reasonable or dangerous procedure. The use of rodents allows experimentation with sufficient number of animals and could provide a picture of both functional and morphological consequences of RON. Therefore, the aim of the present report was to analyze RON outcomes in normal rat eyes. Methods:Male Wistar rats were subjected to RON in one eye, whereas the contralateral eye was subjected to a sham procedure. RON was performed as follows: eyes were focused under a binocular Colden surgical microscope with coaxial light and a scleral puncture, using a 30-G needle, was made at 1 mm of the corneoscleral limbus and a cut was performed in the edge of the neuro-retinal ring, cutting an equal part of optic nerve and retina parapapillary, avoiding the central retinal vessels. The sham operated eyes were submitted to a similar procedure, without the cutting step. After surgery, the surgical outcomes were evaluated in terms of: IOP (assessed by a TonoPen XL), flash electroretinograms (ERG, with a gold electrode), flash visual evoked potential (VEPs, using skull-implanted electrodes) and consensual pupil light reflex assessment, as well as optic nerve head morphology (examined by light microscopy). Results:A transient decrease in scotopic ERG a- and b-wave amplitude was observed in eyes submitted to RON, which was evident 24 h but not 3 or 7 days after surgery. No changes in flash VEPs, IOP, and consensual pupil reflex were observed between sham and RON operated eyes at 7-day post-surgery. Histologically, the optic nerve showed circumscribed scarring at the site of the incision without significant damage of adjacent nerve fibers. Conclusions:These results support that minor histological alterations and transient functional changes were provoked by RON in normal rat eyes.