Dear Editor,

We thank Singh and Raj for their interest and submit the following, in response to their comments, concerning our report of early chorioretinal anastomosis in non-ischaemic CRVO[1]:

Of the six patients who underwent laser anastomosis two had a successful anastomosis following the first treatment at a single site (33%), two cases were successful after a second attempt at one site (66%), a further case had two treatments and the second treament was at two sites, one further patient had two single treatments, followed by a third treatment at two sites. This left all patients with a functioning anastomosis (100%) as confirmed with fluorescein angiography.

We considered that the intervention was justified as this group have a significant risk of visual deterioration. We did not feel that a sham laser procedure was justified and such a group would further have diluted results and limited recruitment to the different groups. As OCT constitutes an objective measure, this may not be necessary. However in a larger study this may be a practical possibility.

Finally, concerning the reference to Fuller et al.[2], this study focussed on anterior segment neovascularisation and data analysis centred on non-perfused (ischaemic) CRVO and excluded perfused (non-ischaemic) CRVO. It is therefore difficult to comment on this point. Natural history studies are best conducted on a large scale. In our series of untreated patients we did not observe any disc collaterals during the treatment period. This point is, however, of limited significance.

We hope that this information addresses the points raised.

Richard Antcliff, Eric Mayer, Tom Williamson and John Shilling.

References

1. Antcliff RJ, M.E., Williamson TH, Shilling JS., Early chorioretinal anastomosis in non-ischaemic CRVO: a randomised trial. Br J Ophthalmol., 2005. 89(6): p. 780-1.

2. Fuller, J.J., et al., Retinochoroidal collateral veins protect against anterior segment neovascularization after central retinal vein occlusion. Arch Ophthalmol, 2003. 121(3): p. 332-6.

Dear Editor,

We read with interest the article by Antcliff and associates.[1] The authors have compared the macular edema, retinal thickness, visual acuity and cyst height in 11 patients of non ischaemic central retinal vein occlusion (niCRVO) randomized to either observation or laser-induced chorioretinal anastomosis (CRA). Although only 6 patients underwent laser induced CRA, the results are encouraging at six months. There are few issues which we would like to raise.

The incidence of CRAs post CRVO is generally 50% during the natural course and these spontaneously arising CRAs were found to develop at a mean interval of 3.9 months by Fuller et al.[2] Also since the retinal haemorrhages present in a fresh case of CRVO may be partly responsible for decreased visual acuity, an early intervention that does not allow normal recovery may be unjustified. We would recommend reassessment of visual acuity and retinal perfusion at 4 to 6 weeks before resorting to any intervention.

The laser-induced CRAs, as described by McAllister et al have been found to improve macular edema in patients of niCRVO.[3] They could successfully create CRAs in only 33% of the cases with one attempt [3], 54% of cases in more than one attempt [4] and in 43% of the cases with mean 1.8 attempts.[5] Since 20% of the eyes also developed the neovascularization at the site of anastomosis [4], it would be interesting to know the total number of attempts required to create a functional anastomosis in all 6 eyes by Antcliff et al.

Also the authors have reported that they could not mask the patients because of the laser surgery, we would suggest a sham procedure on observation group to overcome this limitation. To summarize, the authors are commended for conducting a randomized study for evaluation of this alternative technique to improve vision in CRVO patients. We agree with the authors that a larger trial with longer follow up duration is needed to reach a conclusion. The issues raised by us can also be utilized when planning future studies.

References

1. Antcliff RJ, Mayer EJ, Williamson TH, J S Shilling. Early chorioretinal anastomosis in non-ischaemic CRVO: a randomised trial. Br. J.Ophthalmol. 2005;89;780-781.

2. Fuller JJ, Mason JO, White MF, et al. Retinochoroidal Collateral Veins Protect Against Anterior Segment Neovascularization After Central Retinal Vein Occlusion. Arch Ophthalmol. 2003;121:332-336.

3. McAllister IL, Constable IJ. Laser-induced chorioretinal venous anastomosis for treatment of nonischemic central retinal vein occlusion. Arch Ophthalmol. 1995 Apr;113(4):456-62.

4. McAllister IL, Douglas JP, Constable IJ, Yu DY. Laser-induced chorioretinal venous anastomosis for nonischemic central retinal vein occlusion: evaluation of the complications and their risk factors. Am J Ophthalmol. 1998 Aug;126(2):219-29.

5. Eckstein M, McAllister I. Laser-induced chorioretinal venous anastomosis for non-ischaemic hemi-central vein occlusion. Clin Experiment Ophthalmol. 2000 Feb;28(1):18-21.