A Comparison of Endonasal Dacryocystorhinostomy With and Without Silicone Tubes

Dacryocystorhinostomy (DCR) is the treatment of choice for epiphora due to nasolacrimal duct obstruction. A passage is created between the lacrimal sac and nasal cavity by removing the layers of bone and mucosa between them. It can be performed via an external (transcutaneous) or endonasal route with equivalent success rates.[1] In order to prevent restenosis of the ostium, silicone tubes are often used to maintain the patency of the newly-created fistula. The tubes are removed between 6 weeks and 3 months post-operatively.

Problems associated with tubes include granuloma formation with secondary infection or adhesions, canalicular lacerations, allergic reaction to the silastic, and discomfort.

There are a number of reports of DCR surgery without tubes which demonstrate an equivalent success rate compared with surgery using tubes; however, these studies have been non-randomised, retrospective reviews.[2-6] The only prospective, randomised controlled study[7] had only 42 participants and did not state at which point during the surgery the randomisation was revealed; unless the allocation occurs after the ostium has been completed there is the risk of bias since the surgeon may (consciously or inadvertently) create a larger ostium in cases where no tubes are to be used.

The purpose of this study is to perform a prospective, randomised controlled study to assess whether the use of tubes affect the long-term success of DCR.

Hypothesis Silicone tubing does not improve success rate of endonasal DCR surgery.

Justification There is a dearth of evidence in the literature from well-conducted studies on the merits of tubes versus no tubes in DCR surgery. Since there are several potential problems with tubes outlined above, and since performing surgery with tubes adds to the cost and duration of surgery, it would benefit patients and healthcare providers to know whether they increase DCR success rate.

The standard surgical technique for endonasal DCR has been described by the principle investigator.[1] The identical procedure would be performed in both groups with the exception that half the patients would have tubes inserted, and half would not.

Objectives To assess functional and anatomical success rates of endonasal DCR surgery with and without silicone tubes.

Research Method Prospective, randomised, controlled, interventional trial.

Statistical analysis The primary end point will be functional success, determined by patient-reported symptoms. This will be assessed a minimum of six months post-operatively. In patients with tubes these will be removed at 3 months post-operatively.

The operation will be considered successful if the patient is free of symptoms of a watering eye. It will be considered partially successful if the patient has noticeable improvement but still may experience tearing under certain situations. The operation will be deemed a failure if the patient continues to have symptoms that are no better or worse than pre-operatively.

The secondary end point will be anatomical success, as measured by patency of nasolacrimal irrigation at 6 months post-operatively. In patients with tubes these will be removed at 3 months post-operatively. The operation will be considered successful if there is free flow on irrigation with no reflux. It will be considered partially successful if the nasolacrimal duct is patent but there is more than 50% reflux as assessed by an experienced oculoplastic surgeon. It will be considered a failure if there is more than 50% reflux.

The secondary end point will be anatomical success, as measured by patency of nasolacrimal irrigation at 6 months post-operatively.

Statistical analysis planned From a previous study by the PI[1] (and also from numerous other studies in the ophthalmic literature) the baseline success rate for endonasal DCR with tubes is 90%. The current trial is a non-inferiority study, ie to demonstrate that surgery without tubes is not inferior to surgery with tubes.

In order to demonstrate non-inferiority, the recommended approach is to pre-specify a margin of non-inferiority in the protocol. After study completion, a two-sided 95% confidence interval for the true difference between the two agents will be constructed.[8]

Planned sample size A sample size of 200 (100 participants in each arm of the trial) is expected to give a 95% confidence interval of width of approximately 0.15 ie +/- 7.5% around the estimated difference in success rates.

References

1. Dolman PJ. Comparison of external dacryocystorhinostomy with nonlaser endonasal dacryocystorhinostomy. Ophthalmology. 2003 Jan;110(1):78-84
2. Smirnov G, Tuomilehto H, Teräsvirta M, Nuutinen J, Seppä J. Silicone tubing after endoscopic dacryocystorhinostomy: is it necessary? Am J Rhinol. 2006 Nov-Dec;20(6):600-2
3. Mortimore S, Banhegy GY, Lancaster JL, Karkanevatos A. Endoscopic dacryocystorhinostomy without silicone stenting. J R Coll Surg Edinb. 1999 Dec;44(6):371-3
4. Kashkouli MB, Parvaresh M, Modarreszadeh M, Hashemi M, Beigi B. Factors affecting the success of external dacryocystorhinostomy. Orbit. 2003 Dec;22(4):247-55
5. Beigi B, Westlake W, Chang B, Marsh C, Jacob J, Chatfield J. Dacryocystorhinostomy in south west England. Eye. 1998;12 ( Pt 3a):358-62.
6. Unlü HH, Oztürk F, Mutlu C, Ilker SS, Tarhan S. Endoscopic dacryocystorhinostomy without stents. Auris Nasus Larynx. 2000 Jan;27(1):65-71
7. Smirnov G, Tuomilehto H, Teräsvirta M, Nuutinen J, Seppä J. Silicone tubing is not necessary after primary endoscopic dacryocystorhinostomy: A prospective randomized study. Am J Rhinol 22, 214-217, 2008
8. http://www.emea.europa.eu/pdfs/human/ewp/215899en.pdf