We read with interest the article by Nagpal et al.1 The authors have described the results of early radial optic neurotomy (RON) in an uncontrolled series of 24 patients with non ischaemic central retinal vein occlusion (niCRVO). They have found significant improvement in best corrected visual acuity (BCVA) and foveal thickness at six months follow-up. Although the strong points of this study are the large sample size, strict inclusion criterion and prospective nature, there are few issues which we would like to raise.
The incidence of chorioretinal anastmosis CRAs post CRVO is generally 50% during the natural course and these spontaneously arising CRAs were found to develop at a mean interval of 3.9months by Fuller et al.2 RON leads to the development of CRAs at the neurotomy site in 42-46% cases.34 It will be interesting to discuss why the authors failed to document CRA in any of the cases.
The authors suggest improved blood flow by relieving mechanical pressure on CRV as one of the mechanisms responsible for clinical improvement seen post RON, which needs to be confirmed by a controlled experiment on retinal haemodynamics. On the contrary, a recent study evaluating the effects of RON on retinal circulation in patients with CRVO by indocyanine green (ICG) videoangiography and a computer-assisted image analysis found little improvement in blood flow in the absence of CRAs.4
On the subgroup analysis of the data provided in Table 1, we found that improvement in BCVA seen in cases presenting within four weeks (6 patients) was 0.2 (average decimal acuity) as compared to 0.1 seen in all patients. While this may suggest that an early RON at or before four weeks is more beneficial, the possibility of spontaneous improvement resulting from the resolution of the retinal haemorrhages present in a fresh case of CRVO exists. This emphasises the need for a prospective randomized trial to evaluate the role of early RON. Intravitreal triamcinolone acetonide (IVTA) has been found to decrease the macular oedema and improve BCVA in CRVO although the effect is not sustained. We have also found very encouraging results. (Figure 1a and b). We recommend IVTA in a fresh case (< 4 weeks) and reassessment of visual acuity and retinal perfusion at 4 to 6 weeks before resorting to RON. The resolution of the macular and peripapillary retinal oedema will also assist in selecting the site for RON.
1. Nagpal M, Nagpal K, Bhatt C, Nagpal PN. Role of early radial optic neurotomy in central retinal vein occlusion Indian J Ophthalmol. 2005;53:115–20
2. Fuller J J, Mason JO, White MF, McGwin G, et al Retinochoroidal collateral veins protect against anterior segment neovascularization after central retinal vein occlusion Arch Ophthalmol. 2003;121:332–6
3. Garciia-Arumii J, Boixadera A, Martinez-Castillo V, Castillo R, Dou A, Corcostegui B. Chorioretinal anastomosis after radial optic neurotomy for central retinal vein occlusion Arch Ophthalmol. 2003;121:1385–91
4. Nomoto H, Shiraga F, Yamaji H, Kageyama M, Takenaka H, Baba T, Tsuchida Y. Evaluation of radial optic neurotomy for central retinal vein occlusion by indocyanine green videoangiography and image analysis Am J Ophthalmol. 2004;138:612–9