Sir,

We read the article on ‘Effects of Merogel coverage on wound healing and ostial patency in endonasal endoscopic dacryocytorhinostomy for primary chronic dacryocystitis’ by Wu et al1 with great interest. The surgical procedure involved in this randomized controlled trial was clearly presented and reproducible, and the paper made excellent use of both per-protocol and intention-to-treat analyses in interpretation of the data. We had the following observations regarding the methodology and interpretation of the results.

The diagnosis of primary chronic dacryocystitis was made on the basis of a history of epiphora with purulent discharge and regurgitation on nasolacrimal irrigation. Unfortunately, either no attempt was made to locate the level of obstruction or it was not reported. Many factors influence the outcome of endoscopic dacryocystorhinostomy, and one of the most important prognostic factor is the level of obstruction in the lacrimal system.2, 3 A recent study from South Korea showed that the ductsac junction obstruction was treated most successfully, followed by nasolacrimal obstruction, common canaliculus obstruction, and saccal obstruction.4

Various clinical tests are available to identify the level of obstruction of the lacrimal system. Simple tests such as probing and Jones test can identify punctual and canalicular obstruction, and can be performed in the office. Dacryocystography is considered the gold standard and can localize obstruction within the lacrimal sac or duct.5

If the authors had data on the individual patient's level of obstruction of the lacrimal system, a subgroup analysis should be performed to further analyse the effect and safety profile of Merogel on the different levels of obstruction.

Once again, we would like to congratulate the authors for this successful and nicely performed randomized controlled trial that demonstrated the effect of Merogel on wound healing and ostial patency in endonasal endoscopic dacryocystorhinostomy for primary chronic dacryocystitis.