silicone intubation of the lacrimal system has become very popular in the treatment of congenital nasolacrimal duct obstructions ( cnldo ) resistant to conservative therapy and/or probing [ 16 ] .
bicanalicular intubation ( bci ) has been used since the 1970s , and various techniques have been described , whereas monocanalicular intubation ( mci ) was not popular until the early 1990s [ 1 , 68 ] .
each of these intubation systems has advantages and disadvantages [ 2 , 3 , 57 , 9 ] . whereas the bicanalicular system requires passing a tube through the inferior and superior puncta and through the lacrimal system into the nose , the monocanalicular system requires a single pass of the tube through the system [ 1 , 2 , 4 ]
nevertheless , a comparison of the two kinds of intubation to determine which is optimal has not been well - performed so far .
the objective of this study was to compare the success rate and complications of mci and bci in children treated for cnldo .
the aim of this prospective study was to compare the success rate of mci and bci silicone intubations in the treatment of children with cnldo .
the study was performed in accordance with the declaration of helsinki , good clinical practice , and applicable regulatory requirements .
informed written consent was obtained from all parents / guardians before the initiation of any procedure .
children aged between 12 and 36  months with severe cnldo symptoms resistant to conservative therapy and two probings were included in the study .
the diagnosis of cnldo was based on a history of tearing , the fluorescein dye disappearance test ( fdt ) , and diagnostic probing and/or irrigation tests .
the study was carried out from january 2006 to november 2009 , and a total of 70 eyes ( in 53 children ) were included .
children younger than 10  months of age were excluded because of known self - resolution during maturation of the nasolacrimal duct .
patients with previous eyelid and/or lacrimal surgery , punctal and/or canalicular obstructions , eyelid malpositioning , and less than 6  months follow - up were also excluded .
the study started with 35 consecutive cases of bci ( group i ) followed by 35 consecutive cases of mci ( group ii ) .
the silicone tubes were removed 3 to 4  months after the surgery , and the children were followed up for 6  months .
the drainage function of the lacrimal system was assessed using a combination of the fdt , medical history and clinical examinations ( tear retention and conjunctival sac evaluation , medial canthus observation and/or palpation ) , as well as syringing of the system in some cases , as required .
complete therapeutic success was defined as fdt grade 01 , and this result had to correspond with a complete resolution of previous symptoms .
failure was defined as the absence of improvement or the worsening of the symptoms . for the statistical analysis -test , fisher 's exact test , and the two - sample t - test
were used , with the level of significance set at p  <  0.05 . after probing the lacrimal pathways with the help of a bowman probe , endoscopy of the inferior meatus with the help of a rigid hopkins endoscope , 30 and 2.7  mm in diameter ,
was performed after infraction of the inferior concha . if the probe was placed submucously , a focused incision of the mucous membrane was made , and the end of the probe was released in the inferior nasal meatus . for intubations ,
bicanalicular and monocanalicular silicone sets were used ( ella - cs , m. horkov 504 , 500 06 hradec krlov , czech republic , phone + 420 495 279 111 , www.ellacs.cz ) . after probing the lacrimal system through the inferior canaliculus with a metal probe in the bicanalicular set , a titanium sling
was then put on the tip of the probe into the inferior meatus under endoscopic control , and the metal probe was pulled out of the nose by pulling the handle of the sling and pressing down on the ocular end of the probe . after introducing the other probe of an intubation set into the lacrimal pathways through the upper lacrimal punctum ,
the probe was also pulled out of the inferior nasal meatus in the same way .
the whole procedure was completed by knotting both tubes and placing the knot into the inferior nasal meatus . for the monocanalicular intubation
setting , the silicone tube ( with the ocular anchor and flange ) atraumatically connected with the metal rod was inserted through the lower canaliculus in a similar way ( fig .  1 ) .
the nasal end of the metal rod was then pulled into the nose and the ocular end of the tubing was fixed in the punctual ampulla and secured with a punctual anchor , while the tube was gently tracted on the distal ( nasal ) end .
after punctual footplate placement , the distal end of the tubing was cut and left to dangle freely in the inferior nasal meatus . 

1monocanalicular intubation set ( ella - cs , czech republic )  in detail monocanalicular intubation set ( ella - cs , czech republic )  in detail
when removing the bci while the patient was under local anaesthesia , the silicone tube was removed after the knot had been drawn up through the lacrimal pathways into the conjuctival sac .
the mci was removed by pulling it out with forceps at the lacrimal punctum while the patient was under local anaesthesia .
the aim of this prospective study was to compare the success rate of mci and bci silicone intubations in the treatment of children with cnldo .
the study was performed in accordance with the declaration of helsinki , good clinical practice , and applicable regulatory requirements .
informed written consent was obtained from all parents / guardians before the initiation of any procedure .
children aged between 12 and 36  months with severe cnldo symptoms resistant to conservative therapy and two probings were included in the study .
the diagnosis of cnldo was based on a history of tearing , the fluorescein dye disappearance test ( fdt ) , and diagnostic probing and/or irrigation tests .
the study was carried out from january 2006 to november 2009 , and a total of 70 eyes ( in 53 children ) were included .
children younger than 10  months of age were excluded because of known self - resolution during maturation of the nasolacrimal duct .
patients with previous eyelid and/or lacrimal surgery , punctal and/or canalicular obstructions , eyelid malpositioning , and less than 6  months follow - up were also excluded .
the study started with 35 consecutive cases of bci ( group i ) followed by 35 consecutive cases of mci ( group ii ) .
the silicone tubes were removed 3 to 4  months after the surgery , and the children were followed up for 6  months .
the drainage function of the lacrimal system was assessed using a combination of the fdt , medical history and clinical examinations ( tear retention and conjunctival sac evaluation , medial canthus observation and/or palpation ) , as well as syringing of the system in some cases , as required .
complete therapeutic success was defined as fdt grade 01 , and this result had to correspond with a complete resolution of previous symptoms .
failure was defined as the absence of improvement or the worsening of the symptoms . for the statistical analysis -test , fisher 's exact test , and the two - sample t - test
were used , with the level of significance set at p  <  0.05 .
after probing the lacrimal pathways with the help of a bowman probe , endoscopy of the inferior meatus with the help of a rigid hopkins endoscope , 30 and 2.7  mm in diameter , was performed after infraction of the inferior concha . if the probe was placed submucously , a focused incision of the mucous membrane was made , and the end of the probe was released in the inferior nasal meatus . for intubations ,
bicanalicular and monocanalicular silicone sets were used ( ella - cs , m. horkov 504 , 500 06 hradec krlov , czech republic , phone + 420 495 279 111 , www.ellacs.cz ) . after probing the lacrimal system through the inferior canaliculus with a metal probe in the bicanalicular set , a titanium sling
was then put on the tip of the probe into the inferior meatus under endoscopic control , and the metal probe was pulled out of the nose by pulling the handle of the sling and pressing down on the ocular end of the probe . after introducing the other probe of an intubation set into the lacrimal pathways through the upper lacrimal punctum ,
the probe was also pulled out of the inferior nasal meatus in the same way .
the whole procedure was completed by knotting both tubes and placing the knot into the inferior nasal meatus . for the monocanalicular intubation setting , the silicone tube ( with the ocular anchor and flange ) atraumatically connected with the metal rod was inserted through the lower canaliculus in a similar way ( fig .  1 ) .
the nasal end of the metal rod was then pulled into the nose and the ocular end of the tubing was fixed in the punctual ampulla and secured with a punctual anchor , while the tube was gently tracted on the distal ( nasal ) end .
after punctual footplate placement , the distal end of the tubing was cut and left to dangle freely in the inferior nasal meatus . 

1monocanalicular intubation set ( ella - cs , czech republic )  in detail monocanalicular intubation set ( ella - cs , czech republic )  in detail
when removing the bci while the patient was under local anaesthesia , the silicone tube was removed after the knot had been drawn up through the lacrimal pathways into the conjuctival sac .
the mci was removed by pulling it out with forceps at the lacrimal punctum while the patient was under local anaesthesia .
bicanalicular intubation was performed in 35 eyes ( 24 children ; group i ) and monocanalicular in 35 ( 29 children ; group ii ) .
the youngest patient was 10  months of age and the oldest was 32  months of age ( fig .  2 ) .
tubes were usually removed between 3 and 4  months after the surgery in an office setting ( figs .  3 , 4 ) . 

2monocanalicular intubation showing the position of the flange on the eyelid margin after tube fixationfig . 
4monocanalicular intubation in cnldo ; success rate according to age monocanalicular intubation showing the position of the flange on the eyelid margin after tube fixation bicanalicular intubation in cnldo ; success rate according to age monocanalicular intubation in cnldo ; success rate according to age in group i , complete resolution of symptoms was observed in 29/35 cases ( 82.86% ) , partial resolution in 2/35 ( 5.71% ) , and failure in four cases ( 11.43% ) ( table  1 ) . in group ii , the complete resolution of symptoms was observed in 31/35 eyes ( 88.57% ) , partial success in 3/35 eyes ( 8.57% ) , and failure in 1/35 eyes ( 2.86% ) .
therefore , complete and partial success was achieved in 31/35 ( 88.57% ) in group i and in 34/35 ( 97.14% ) in group ii .
the success rate ( complete + partial success ) in group ii ( mci ) was not significantly higher than that of group i ( bci ) ( p  =  0.584 ) .
table  1comparison of the bicanalicular and monocanalicular intubation resultsoutcomegroup i : bicanalicular intubation ( 35 cases)group ii : monocanalicular intubation ( 35 cases)complete resolution29 ( 82.86%)31 ( 88.57%)partial resolution2 ( 5.71%)3 ( 8.57%)failure4 ( 11.4%)1 ( 2.86%)total31/35 ( 88.57%)34/35 ( 97.14% ) comparison of the bicanalicular and monocanalicular intubation results dislodging of the tube and premature removal was observed in four cases in group i ( 1 , 2 , 4 , and 8  weeks after intubation respectively ) , whereas loss of the tube was observed twice ( 1  week after intubation in one case , and in one case the parents did not specify the time of the loss ) in group ii ( table  2 ) . in children with premature tube removal ,
improvement of symptoms was observed in 3/4 eyes in group i ( 75.0% ) , and in 2/2 eyes in group ii ( 100.0% ) . 

table  2comparison of the complications observed with bicanalicular ( bci ) and monocanalicular intubation ( mci)complications / numbergroup i bcigroup ii mcidisplacement and premature removal4-loss-2granuloma pyogenicum-2corneal abrasion / ulcer-1canalicular slitting5-inflammation of the lacrimal system-- comparison of the complications observed with bicanalicular ( bci ) and monocanalicular intubation ( mci ) slitting of the punctum and canaliculi were observed in five eyes with bci ( group i ) and none with mci ( group ii ) .
granuloma pyogenicum was found in two cases with mci and completely revealed during 2  months after tube removal without any specific treatment .
corneal erosion in the inferior medial quadrant was observed in one eye treated with mci shortly after tube placement , and resolved within a few days after local treatment ; it was not necessary to remove the tube prematurely .
dislodging of the tube and premature removal was observed in four cases in group i ( 1 , 2 , 4 , and 8  weeks after intubation respectively ) , whereas loss of the tube was observed twice ( 1  week after intubation in one case , and in one case the parents did not specify the time of the loss ) in group ii ( table  2 ) . in children with premature tube removal ,
improvement of symptoms was observed in 3/4 eyes in group i ( 75.0% ) , and in 2/2 eyes in group ii ( 100.0% ) . 

table  2comparison of the complications observed with bicanalicular ( bci ) and monocanalicular intubation ( mci)complications / numbergroup i bcigroup ii mcidisplacement and premature removal4-loss-2granuloma pyogenicum-2corneal abrasion / ulcer-1canalicular slitting5-inflammation of the lacrimal system-- comparison of the complications observed with bicanalicular ( bci ) and monocanalicular intubation ( mci ) slitting of the punctum and canaliculi were observed in five eyes with bci ( group i ) and none with mci ( group ii ) .
granuloma pyogenicum was found in two cases with mci and completely revealed during 2  months after tube removal without any specific treatment . corneal erosion in the inferior medial quadrant
was observed in one eye treated with mci shortly after tube placement , and resolved within a few days after local treatment ; it was not necessary to remove the tube prematurely .
silicone intubation was first described by quickert and dryden in 1970 and the procedure has become part of the standard management of cnldo [ 2 , 3 , 6 ] . among the factors that affect the treatment success of cnldo
are age , severity of symptoms , the history of previous interventions , time of the interventions , and compliance with treatment .
however , there are no generally accepted and defined rules concerning age , length of intubation , and/or different variations in intubation systems [ 6 , 11 ] .
although tube placement in children requires general anesthesia , the normal anatomy of the lacrimal system is not destroyed , and the success rates range from 80% to 100% [ 13 , 6 , 12 ] .
bci has been used more frequently , not only for treatment of cnldo , but also for dacryocystorhinostomy , canalicular stenose , etc . [ 2 , 6 ] .
one of the factors that may determine whether or not to use bci or mci is the number of complications [ 13 , 6 ] .
one of the main advantages of bci is that bci is generally very well - tolerated by the cornea because it is significantly smoother than mci [ 1 , 7 , 9 ] .
if mci is used , corneal abrasions or ulcers can be caused by the ocular end of the mci .
the abrasions usually occur in the inferior nasal quadrant ( if the tube is fixed in the the inferior canaliculus ) , and usually heal in a few days after local treatment .
observed only three ( 1.5% ) corneal ulcers in 223 eyes with mci , whereas no corneal ulcers were observed in 1,620 bci placements .
they assumed that the placement of the mci in the superior canaliculus is a predisposing factor for corneal irritation , especially if the size and length of the collarete is larger . on the other hand , engel et al .
recommend performing mci through the superior canaliculus , and found only a 2% risk of conjunctival or corneal abrasions in their series of 635 eyes . in our study ,
in which monocanalicular tubes were inserted into the inferior canaliculus , corneal abrasion was observed in only one child ( 2.8% ) a few days after the surgery .
our experience confirms that it is necessary to use tubes of an appropriate size with a small flange ( collar ) that does not exceed the eyelid margin and does not irritate the cornea , so that corneal abrasion and ulceration is prevented .
conversely , fayet et al . found the diameter of the collar to be unimportant and without influence on the rate of corneal erosions .
mci offers a chance to achieve better success rates than simple probing , and requires only a single pass through the nasolacrimal system .
the technical insertion of mci as well as its removal is easy , and the difficulties associated with bci are minimized [ 1 , 4 ] . based on our 17  years of experience with lacrimal surgery , we agree that the manipulation in only one canaliculus may be advantageous because the risk of possible iatrogenic traumatisation of the lacrimal system is lower .
unexpected side - effects should be taken into consideration , too . while we observed no granuloma pyogenicum in the bci group , we observed two granulomas in children who had mci . though these occurences resolved a few weeks after removal of the tube , they seem to be related to the ocular end of mci .
fayet et al . recommended not leaving a mci in for longer than 3  months to decrease the likelihood of complications .
while we usually removed mcis within 3 to 4  months after placing the tubes , the question of whether or not the number of complications would increase with longer mci placement is unclear . in our study , there were only two children with a longer ( 5 and 11  months respectively ) tube placement ( they did not return for removal of the tube until these times ) ; however , no complications were observed in these two cases , and full success was achieved . in order to prevent damage to the punctum and fibrous meatal ring while inserting the mci ,
fayet , who developed the monoka system ( fci , france ) , recommends only gentle traction on the distal end at the time of insertion and gentle dilation of the punctum [ 7 , 9 ] .
a special dilator for inserting the tube can help to avoid inadvertent damage to the puntal and canalicular systems .
although we did not use this dilator , no difficulties during the time of tubing were observed . on the other hand , excessive dilation might increase the incidence of some complications , especially spontaneous loss of the tubing .
this complication was observed in 35.4% in a study of 48 eyes with cnldo treated with mci reported by kaufman and guay - bhatia , where premature removal was observed in 21 of 48 eyes ( 43.7% ) .
dislodgement of bci causing premature removal was observed in four eyes , whereas premature loss of the monocanalicular tube was observed twice .
the success rates of bcis for the treatment of cnldo range from 83% to 100% [ 2 , 6 , 11 , 12 ] .
observed complete resolution of epiphora in 67.7% with monoka and 62.4% with bci in their study of 120 cases . in their study comparing mci and bci in 48 eyes of adults , kashkouli et al .
achieved nearly the same complete success rate ( mci 61.5% , bci 59.0% ) ; moreover , higher partial success and lower failure rate was achieved than in the group with bci . in our study , we found no significant differences in the sucess rates between the bci ( 88.5% ) and mci ( 97.1% ) groups . on the other hand , in the study by kaufman et al .
of 48 eyes with mci , full and partial success was achieved in only 30 cases ( 78.0% ) , and 21 cases of premature tube removal occurred ( 43.7% ) . in the study by engel et al .
of 635 children with probing and mci , the success rate was 97% , declining to 90% when surgery was performed in infants older than 24  months of age .
that , for those patients with cnldo requiring general anesthesia , mci may reduce recurrence and reoperations , and is an appropriate alternative in the treatment of cnldo .
our results raise the question of whether or not it would be better to prefer mci over bci in the treatment of cnldo . although our study supports a preference for mci , further prospective
, randomised studies would better determine the advantages and disadvantages of the two intubation methods .
mci is very effective in the treatment of cnldo , and is an appropriate alternative procedure with a minimum of complications . the success rates of mci and bci were not significantly different .
the use of monocanalicular intubation is easier to perform ; thus , it is a useful method for the treatment of cnldo resistant to conservative therapy and probing .
 backgroundto compare the success rate of monocanalicular intubation ( mci ) compared with bicanalicular silicone intubation ( bci ) in congenital nasolacrimal duct obstruction ( cnldo ) in infants and toddlers.methodsin a prospective , nonrandomized , comparative study , 
 mci ( n  =  35 eyes ) through the inferior canaliculus or bci ( n  =  35 eyes ) were performed under general anaesthesia in children aged 10 to 36  months with cnldo . 
 the tubes were removed 34  months after tube placement , and the children were followed up for 6  months after the removal of tubes . 
 therapeutic success was defined as the fluorescein dye disappearance test grade 01 , corresponding with a complete resolution of previous symptoms . 
 partial success was defined as improvement with some residual symptoms.resultscomplete and partial improvement was achieved in 31/35 ( 88.57% ) in the bci group and 34/35 ( 97.14% ) in the mci group . 
 the difference between the two groups was not significant ( p  =  0.584 ) . 
 complications occurred in both groups . 
 dislodgement of the tube and premature removal was observed in four bci cases , and loss of the tube was observed twice in the mci group . 
 canalicular slitting was observed in five eyes in the bci group . 
 granuloma pyogenicum observed in 2 cases with mci revealed a few weeks after the tube removal . 
 corneal erosion in the inferior medial quadrant was observed in one mci eye and revealed in a few days after the local treatment without tube removal.conclusionsboth mci and the bci are effective methods for treating cnldo . 
 mci has the advantage of a lower incidence of canalicular slit and easy placement.electronic supplementary materialthe online version of this article ( doi:10.1007/s00417 - 011 - 1700 - 2 ) contains supplementary material , which is available to authorized users . 
Electronic supplementary material
Introduction
Materials and methods
Study design
Time points and follow up clinical examinations
Procedure technique
Results
Complications
Discussion
Conclusion
Electronic supplementary material