There are not many studies that examined the effect of tube diameter differences on the prognosis of PANDO treatment. Several reports introduced attempts to prevent restenosis after tube removal by enlarging the lacrimal duct after surgery. One method is to insert two 0.64mm Crawford tubes into the canaliculus. 10,27,28 These studies reported a higher patency rate after canaliculoplasty for pre-saccal obstruction. Another study showed that double silicone intubation of a 0.64mm Crawford tube and a 0.94mm single wide-diameter Crawford tube were equally effective.25 Our study demonstrated that one year after NST intubation for post-saccal obstruction, the patency rate was 0.857 (0.754 - 0.919) when a 1.5 mm thick tube was utilized and 0.739 (0.617 - 0.828) when a standard 1.0 mm diameter tube was applied. Furthermore, comparison of survival rates between the two groups by the RMST method showed that the patency rate of the LD group was significantly higher, suggesting that the larger diameter tubes had better outcomes in post-saccal obstruction.
1.5 mm diameter NST was developed and applied clinically in recent years. As a result, the period for determining the effectiveness became shorter than that of the conventionally used 1.0 mm NST. Therefore, the RMST method was applied to compare the treatment efficacy between the two groups because the proportional hazard property was not established in the late stage of the Kaplan-Meier curve. The τ of RMST was determined as 365days, considering the following conditions. 1) Clinically, recurrence was mostly observed within one year after tube removal. 2) In our institution, follow-up was usually completed without recurrence for one year after tube removal. 3) The ratio of censoring in Kaplan-Meier's curve increases after one year of removal due to reasons such as completion of follow-up or transfer to other facilities.
Additionally, compared to the preconditions between the two groups, the preoperative obstruction period was significantly longer in the ND group. Previous studies identified that the preoperative occlusion period conferred as a risk for recurrence after silicone intubation.29 Therefore, we performed a logistic regression analysis of the involvement of the preoperative obstruction period in recurrence between the two groups; however, we found no significant correlation in our cohort (p = 0.69).
In general, the long-term therapeutic outcomes of ENDI are not equivalent to DCR. Nevertheless, evidence has accumulated that the outcomes of ENDI are almost as effectual as DCR for canaliculus obstruction and PANDO (in cases of non-inflammatory or partial obstruction). 15,17,18,29−31 However, it has been reported that patients with prolonged preoperative occlusions, extended length obstruction, or a history of dacryocystitis tend to relapse after ENDI treatment. 17,22,29,31,32 Since ENDI is a minimally invasive procedure for the treatment of PANDO, which can be performed under local anesthesia, and there are various advantages in terms of surgical time, facial surgical scars, bleeding, and downtime compared to DCR. 3,4,11,17,18,22,23,31,33 ENDI can also be performed in patients receiving systemic anticoagulation and antiplatelet therapy because the risk of bleeding is minimal. Hence, further studies are needed to compare the long-term treatment outcomes of DCR and ENDI in PANDO, in terms of pathological conditions (e.g., site of obstruction, cause of obstruction, and duration of obstruction).
This study involves several limitations. First, this study was a single facility retrospective cohort study; thus, long-term follow-up was limited. It is necessary to evaluate the prolonged outcomes with a larger number of postoperative patients in a multi-center study. Second, since 1.5 mm NST was recently applied clinically, the period to evaluate its efficacy was relatively shorter than that of the conventional 1.0 mm NST. The long-term outcome of the 1.5 mm NST requires extended follow-up time to be determined.
In conclusion, this is the first report to compare the postoperative patency rate of silicone tube intubation for post-saccal obstruction according to the difference in tube caliber. We propose that the use of larger diameter tubes could provide improved therapeutic outcomes.