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We read with interest the article by Gouws et al1 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 has been 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 anterior2,3 and posterior4,5 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 phototoxicity from the operative microscope6 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 suboptimal 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 may be reduced.
We thank Lam et al for their interest. In response to their comments, as stated in the article and demonstrated in figures 1B and C, the effect persists when co-morbidity such as diabetes is removed.
Both groups’ surgery was performed by the same surgeon who did not have juniors attached to the list.
Not all patients had dilated fundus examination postoperatively. Clinically significant cystoid macular oedema (CMO) is unlikely in patients with visual acuities of 6/12 or better, although subclinical CMO can be demonstrated in up to 20% with fluorescein angiography.1
This retrospective study on a unique cohort of patients provided us with the opportunity to demonstrate a potential side effect with the use of trypan blue. A prospective trial is required to control for all the variables and confirm or refute our findings.Please give a fuller address, like town, country!!
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