The laser is first used to ablate mucosa around the area where the light-pipe is most readily seen. The bone is then ablated over an area of 0.5-0.8 cm (Fig. 14.14). It is important to be guided by the light in the sac and not to follow the reflection of the aiming beam, which could potentially lead to the creation of a false passage.
Contact with the bone maximizes ablation as delivery of laser energy through a fiber does not deliver parallel light and its energy dissipates the further the fiber is from the tissue. Fumes can be sucked out with a sucker placed in the nose, or there are delivery devices that have a suction channel alongside the port that delivers the laser fiber. If bony ablation is suboptimal, it can leave a residue of charcoal. The laser will not be able to ablate charcoal, and charcoal will dissipate energy, causing damage to the surrounding tissue. If charcoal collects, it is best to curette it away; this is easily done with a chalazion curette or House curette.
Once the sac is exposed, the light-pipe should be withdrawn from the sac so that the laser does not puncture a hole in its metal sleeve, which may then become rough and can potentially tear the common canaliculus when it is withdrawn. A lacrimal probe is placed to help tent the sac medially and this will help open it up with the laser. The sac is opened, being sure not to cause damage to its lateral wall. Once the sac has been opened to form a rhinostomy of 0.5-0.8 cm, silastic stents can be placed in the lower and upper canaliculi and retrieved in the nose before they are passed through a Watskie sleeve (Fig. 14.15). A knot is tied in the stents to stop the sleeve slipping off. The loop should not be so tight that the sleeve is pressing on the rhinostomy as this produces more granulations and the stent may "cheese-wire" through the canaliculi. Cheese-wiring destroys the pump system and should be avoided at all costs.
Silastic stents are supplied with metal introducers, and these can be bent and passed through the canaliculi. An alternative technique is to pass the stents through an introductory cannula; we believe that this causes less mucosal damage to the canaliculi and common canaliculus. The cut 3 cm end of the sleeve of an intravenous cannula can be passed through each canaliculus in turn over a 1/0 probe. The probe is then removed and the stent is passed through the abbocath and retrieved in the nose. When this is repeated through the other canaliculus, both the stent and the cannula are retrieved. The cannula is then removed before a silastic sleeve is fed over the stents and a knot is made to help secure the loop of tubing (Barki et al., 1998).
Advantages of laser DCR:
1 There is no external scar.
2 It can be done as an outpatient procedure.
3 It can be done in those who are not fit for general anaesthetic, e.g., with severe cardiovascular disease or on warfarin.
4 There is minimal bleeding and primary and secondary hemorrhage rates are low.
5 Short operating time.
Disadvantages of laser DCR:
1 Laser precautions are required.
3 There is a higher failure rate. (It is not easy to compare the results of external DCR or conventional endoscopic DCR with laser endonasal DCRs because the selection criteria used in the reported series differ, e.g., in the incidence of co-existing proximal block and the criteria for success. Many studies define "success" as the patient not returning: this is not satisfactory. Review of the evidence that is available suggests that laser DCR may induce more scarring and have a 10% lower success rate at approximately 12 months, so the relative advantages and disadvantages of this technique need to be presented to the patient to help them decide which operation to have.)
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