Dear Editor

We read with interest the article by Gouws et al.[1] on the apparent increased incidence of cystoid macular oedema (CMO) in phacoemulsification patients when trypan blue was used to stain the anterior capsule.

Trypan blue was commonly used in both anterior and posterior segment surgeries.[2-4] If trypan blue does cause macular toxicity, its risks should theoretically be higher when used in posterior segment surgeries. However, studies on the use of trypan blue, both in the anterior[2,3] and posterior[4,5] segments, did not show apparent toxicity.

Thus, it would be appreciated if the authors could clarify whether other potential confounders were assessed in their study, including:
1. Other causes of CMO such as diabetes, uveitis and prostaglandin use;
2. Operating time since photo-toxicity from the operative microscope[6] per se is a risk factor for CMO development. It appears that only operations for patients in group B were performed by one surgeon, if operations for patients in group A (with trypan blue use) were done by trainees, the operative time is expected to be longer;
3. Whether all patients received a fundus examination with dilated pupil after the operation. If these were only performed in patients with sub- optimal visual acuities, the incidence of CMO may be underestimated.

Finally, we concur with the authors' view that we should try all means in terms of minimising any theoretical toxicities of trypan blue. It is our routine to actively remove trypan blue with the bimanual irrigation aspiration system as soon as the anterior capsule has been stained. It is very effective and the potential toxicities might be reduced.

References

1. Gouws P, Merriman M, Goethals S, Simcock PR, Greenwood RJ, Wright G. Cystoid macular oedema with trypan blue use. Br J Ophthalmol. 2004 Oct;88(10):1348-9.

2. Melles GR, de Waard PW, Pameyer JH, Houdijn Beekhuis W. Trypan blue capsule staining to visualize the capsulorhexis in cataract surgery. J Cataract Refract Surg. 1999 Jan;25(1):7-9.

3. Dada VK, Sharma N, Sudan R, Sethi H, Dada T, Pangtey MS.Anterior capsule staining for capsulorhexis in cases of white cataract: comparative clinical study. J Cataract Refract Surg. 2004 Feb;30(2):326-33.

4. Feron EJ, Veckeneer M, Parys-Van Ginderdeuren R, Van Lommel A, Melles GR, Stalmans P. Trypan blue staining of epiretinal membranes in proliferative vitreoretinopathy. Arch Ophthalmol. 2002 Feb;120(2):141-4.

5. Li K, Wong D, Hiscott P, Stanga P, Groenewald C, McGalliard J. Trypan blue staining of internal limiting membrane and epiretinal membrane during vitrectomy: visual results and histopathological findings. Br J Ophthalmol. 2003 Feb;87(2):216-9.

6. Donzis PB, DeBartolo DF, Lewen RM, May DR. Light-induced maculopathy and cystoid macular edema. J Cataract Refract Surg. 1988 Jan;14(1):84-5.