This procedure can be conducted under endoscopic or direct visualization. We prefer to perform MICDCR under direct visualization using surgical loupes and a fiberoptic headlight; however, the use of an endoscope may be helpful in patients with difficult anatomy. The major benefit of performing under direct visualization is the ability to use both hands freely, which is especially valuable when bleeding compromises the surgical field. In such cases, the surgeon may hold the suction line in one hand and the surgical instrument in the other to continue performing the procedure without needing an assistant. However, the procedure may also be successfully undertaken using the endoscope, which provides good visibility of the surgical field and help proper placement of the tube. A recent report of endoscopic MICDCR in a series of 15 patients achieved 86.6 % success and no tube extrusion in any of the cases. The authors used straight Jones tube in 60 % of the patients and Gladstone-Putterman tube was preferred in 40 %; the mean tube length being 21 mm [23].

There are several benefits of MICDCR besides the shortened surgery duration. As the minimally invasive character implies, it causes minimal trauma to the patient. There is no skin incision and this is quite important for the young patients and the pigmented population who are at higher risk for keloid or scar formation. The surgery can be undertaken using simple and inexpensive equipment. Another advantage of this surgery is the ability to undertake the procedure using local anesthesia instead of general anesthesia owing to the shorter operative duration and the benefit of minimal blood loss.

Tube length and positioning is an important parameter for the success of surgery. Ideally, the medial end of the tube should not touch the nasal septum (approximately 2 mm from the septum).

The length of the tube depends on the patient anatomy; however, we found that 16 mm tube was appropriate for most of our patients [22]. The flange diameter is also important as the larger diameter will prevent displacement of the tube, but larger tubes will be more irritating to the surrounding tissues including the globe. The standard Pyrex tubes have a 3.5 mm diameter and those are the ones we prefer during MICDCR; however, in a single case of extrusion, we needed to replace the standard tube with a 4.5 mm diameter tube that provided good stabilization.

Conventional CDCR was reported to have a high complication rate. In a series of 49 eyes operated with conventional CDCR between 1984 and 2002, complication rate was reported as 3.5 per patient and the most common complications included extrusion, malposition, medial migration, hypermobility, obstruction, infection, granuloma formation, discomfort, restrictive strabismus, and diplopia [1, 5, 14, 24, 25]. Surgical failure is commonly due to tube migration or incorrect tube positioning. Extrusion or dislocation of the tube was reported to occur as high as 51 % and 33 % respectively [5, 14].

The technique of MICDCR, on the other hand, is associated with few complications. The most common complication in our MICDCR series was tube migration towards the nose seen in 7 of 55 patients. Of these seven patients, successful repositioning was achieved in four patients in office conditions. The other three patients were diagnosed with permanent closure and the tubes were surgically repositioned under local anesthesia. Another patient had recurrent tube migration and was treated by the use of a larger, 4.5 mm flange tube with success. In such cases, the use of frosted tube or a Gladstone-Putterman tube has been recommended [26, 27]. Dailey et al. reported that the frosted tube (Weiss Scientific Glass Blowing Company, Portland, OR) improved stability and decreased extrusion in ten patients followed for 8 months [26]. Other customizable tubes such as the Teflon tube (Dupont, Wilmington, DE), silicone, polypropylene, and polyethylene were also shown to be less likely to migrate or extrude; however, poor capillary attraction with slower flow and higher likelihood of obstruction limited their success [28]. Some authors declared that high-density porous polyethylene (HDPP)-coated tear drain tubes (Medpor, Porex Surgical Inc, Newman, GA, USA) minimized tube extrusion rate [29, 30]. However, the use of Medpor-coated tubes was associated with increased conjunctival overgrowth (23 % compared to 5.7 % with conventional tubes) [29]. They are hard to replace if needed because of the fibrous ingrowth and they may incite conjunctival irritation. To solve the conjunctival irritation and discharge due to this type of material, Abdulhafez recommended modifying the tube by cutting the proximal portion of the HDPP coat, and by this technique, they showed successful outcome with no patient discomfort in a series of ten patients [31].

Massry and Larian described a different technique to manage recurrent tube extrusion in a 62-year-old lady who was reoperated by the authors and received a 17 mm frosted Jones tube which extruded again [32]. The authors decided to place a red rubber catheter around the distal end of the tube to provide mechanical stabilization and the patient was followed for 4 months without any further problems. However, the follow-up was short and then as the authors stated in their paper, this technique would prevent easy removal of the tube when the tube required cleansing or exchange in the future. In an unpublished case, one of the authors of this study (AC) used a similar mechanical plugging idea to provide stability for an early extruding tube; however, instead of an allogenic material, autologous fat was used to provide a snug fit between the mucosa and the distal end of the tube. This provides a natural integration with the mucosa and the autologous character prevents possible future adverse events associated with the foreign material. The fat was acquired from the posterior ear lobe of the patient through a tiny incision. The patient experienced no problems for more than 2 years after this revisional procedure.

Modifications of the tube according to the patient anatomy are definitely important for successful outcome; however, the best way to improve the stability of the tubes is probably through refining the surgical steps. Previous research stated that the main cause of CDCR failure was tube migration or incorrect tube positioning, and that success of surgery could be increased by reducing tube malposition [3, 33]. A number of instruments were used to create the tract properly between the ocular surface and the nasal cavity including cannulae, Kirschner wire (K-wire), and the Cox system [34–36]. The main purpose of such instruments is to make a precise tube insertion; however, since the consecutive steps require removing the dilating instruments before the guide is placed, multiple tracts may be formed causing misdirection or malpositioning of the tube. A modified double component trochar using the Cox system was reported to be helpful to overcome this problem. The authors claimed that the double component trochar reduced operative time and risk of tube displacement [37].

Tube obstruction in the postoperative period is another possible complication associated with Jones tubes usually preventable by educating the patient about frequent cleansing and in-office cleaning by probes at regular intervals. In our series, we never encountered a clogged tube, but in case of severe obstruction that cannot be prevented or managed by conservative measure, tube exchange is mandated. Techniques of tube replacement or exchange may be various. Recently, Eloy et al. described an easy-to-perform in-office tube exchange procedure using the Seldinger technique [38]. In this technique, 3–0 prolene is passed through the tube, tube is removed, and the new tube is inserted over the prolene suture under local anesthesia in office conditions. The reason why MICDCR provides less clogging problem may be due to the more vertical positioning of the tube compared to the conventional technique and due to creating less inflammation and mucosal healing response by the less tissue distortion associated with this technique.

Damage to the middle turbinate or the septum is a possibility during any type of CDCR operation using bypass tubes. In conventional surgery, the Jones tube is angled 10–20° inferiorly, reaching a crowded region inside the nose where the septum and the lateral wall of the nose are in close anatomic proximity. This may cause septum or turbinate deformity either during the operation or postoperatively if the tube touches these structures. Middle turbinate usually requires partial resection to provide adequate space during surgery. This maneuver, however, may lead to nasal adhesions and scarring and therefore preservation of the turbinate has been recommended [39]. In our series however, we have never encountered any such problem due to partial resection of the middle turbinate. We believe that a limited middle turbinectomy that allows a wide space at the nasal end of the tube, performed with special care not to injure the septal mucosa is safe and greatly improves the outcome of the operation, reducing the incidence of reoperations to change the length of the tube.

Another complication we never observed was the postoperative diplopia in our series, while Ashenhurst et al. described eight diplopia cases following their modified CDCR technique in a series of 225 cases [40]. Their surgical technique was very similar to the MICDCR procedure that we described. In their paper, the patients reported diplopia several months to as long as 6 years after surgery. This complication was associated with conjunctival scarring and while symptoms resolved by topical application of corticosteroids in two patients, other six patients required surgical excision of scar tissue, which was successful in only two patients.