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The Official Scientific Journal of Delhi Ophthalmological Society
Lacrimal Stents and Intubation Systems: An Insight

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Manpreet Singh, #Saurabh Kamal, ##Sowmya V 
Consultant, Ophthalmic Plastic and Reconstructive Surgery, Sohana Charitable Eye Hospital, Chandigarh
#Consultant, Ophthalmic Plastic Surgery, Perfect Vision Eye Hospital, Faridabad, Haryana
##Department of Ophthalmology, Father Muller Medical College, Mangalore, Karnataka
Corresponding Author:
Manpreet Singh
Consultant- Ophthalmic plastic surgery and Dacryology services
Sohana Charitable Eye Institute, Mohali, Punjab
Email: drmanu83@gmail.com
Received: 09-MAY-2015 Accepted: 10-JUN-2015 Published Online: 23-JUN-2015
DOI: http://dx.doi.org/10.7869/djo.128
Abstract
Lacrimal stents and intubation systems have been used in past to keep the lacrimal pathways patent after surgery, trauma, reconstruction etc. Recently, its physiological role for functional epiphora has been highlighted. Over the years materials, surgical techniques and various designs have evolved. The precise knowledge about design and proper technique of insertion provides the best possible outcomes in terms of anatomical and functional success for various disorders. The present review aims to provide a comprehensive knowledge of various available lacrimal stents and their role in management of lacrimal disorders.
Keywords : lacrimal, lacrimal stents, lacrimal intubation, dacryocystorhinostomy, canaliculus, canaliculus obstruction, canaliculus stenosis, punctum stenosis, punctum
Applied anatomy of lacrimal drainage system

All ducts and vessel lumina of human body are lined by an epithelium or endothelium whose health and continuity is maintained by the regular physiological cell turnover. The patency of their lumen is essentially maintained by the constant amount and continuous nature of fluid flow through these tracts. Above all, a specific anatomical location demands particular type of epithelial cell lining like ciliated columnar epithelium of respiratory and sinus mucosa which helps in migration of mucous secretions. Same is true for the lacrimal drainage system i.e. lacrimal punctum, canaliculus, sac and nasolacrimal duct (NLD).[1] The non-keratinising stratified squamous epithelium of the canaliculus becomes continuous with that of eyelid margin proximally through the punctum. The non-keratinising pseudostratified columnar lining of the lacrimal sac and nasolacrimal duct (NLD) has got goblet cells and other mucus secreting glands with foci of scattered ciliated respiratory epithelium which is more concentrated in the lower membranous portion of NLD just proximal to valve of Hasner.[1,2]

 
Punctum is the most proximal opening of lacrimal drainage system which is surrounded by a ring of dense sclerous fibrous tissue acting as sphincter.[3] The normal shape of punctum changes from being circular in childhood to oval in elderly. The normal punctum size ranges from 0.2-0.5 mm, and size less than this can be theoretically labelled as punctal stenosis.[4] Punctum lies medial to the medial most meibomian gland opening on eyelid margin and this landmark helps to locate it while performing punctum recanalisation procedures for a severely stenosed and sometimes undetectable punctum.

It has now been proven via anatomical and optical coherence tomography studies that the punctum and vertical part (2mm) of canaliculus lies in tarsal plate and is incompressible.[5] The horizontal portion of canaliculus is composed of collapsible tube which is surrounded antero-inferiorly by Horner’s muscle, a specialised part of orbicularis oculi participating in lacrimal pump function.[6] The transition of vertical canaliculus into the horizontal portion is formed by a dilated structure called Ampulla. The normal horizontal portion of canaliculus has diameter ranging from 0.5 to 1.5 mm which varies along its length.[3,6] Horizontal canaliculi are elastic structures and can dilate upto 2-3 times during manoeuvres.
 

Any injury or trauma (mechanical, thermal, chemical or radiation) to the epithelial lining and surrounding tissue of lacrimal drainage system can potentially cause an aggressive healing response. This can cause occlusion or fibrotic stenosis of punctal and canalicular lumen. The internal trauma in lacrimal sac and NLD is very rare owing to the relatively distant location, but the soft tissue and the bone surrounding lacrimal sac and NLD undergo specific changes with age or after trauma which make it narrower and ultimately blocked. For e.g. a common OPD procedure like punctum dilatation and lacrimal irrigation can potentially cause gross or micro trauma to the lining epithelium and walls of punctum and canaliculus by their ragged tips and sharp edges. This is further aggravated by the faulty technique causing significant punctal and canalicular stenosis.  

Background of lacrimal stents/ intubation devices

Historically, various types of materials (organic, metal and synthetic) have been used as a stent for stenosed punctum or canaliculi. The first stent use was described by Graue (1932, silver wire), followed by Henderson (1950, polyethylene) and Veir (1962, malleable metal rod).[7,8] Since then, various materials like silk, nylon, dacron and polypropylene have been used and their designs have evolved for better retention and minimum collateral damage. Newer stents have improved the success and reduced complication rates.

Ideally a stent should have all of the following properties: inert, pliable, smooth external surface, self retaining, cheap/affordable, easily available, simple to use and should not cause any mechanical damage to surrounding soft tissues. Medical grade silicone was introduced in 1968 by Keith, has most of the above mentioned desired properties and is mainly used nowadays. Later, Quickert & Dryden (1970) and Crawford (1977) improvised on these intubation devices and reported significant success with bicanalicular stents.[9,10,11] Bruno Fayet (1989) and Ruban (1995) modified those to monocanalicular devices and in 1998, the Ritleng bicanalicular device was introduced.[12,13,14]

Mechanism of action of stents[15]

A.    Functional: The tears can flow along the surface of stent by the capillary action (due to surface tension) and this natural consistent flow of tears helps in keeping the lumen patent. This action is proportionate to the amount of fluid passing through the lumen (Riverbed phenomenon).

B.    Anatomical (or mechanical effect)
  1. When in-situ stents dilate the narrow or stenosed punctum, canaliculi and NLD. Mechanically it increases diameter of lumen and as per Poiseuille’s law (flow rate is proportional to pressure difference divided by viscous resistance, but the fourth power dependence on radius affect is maximal) drainage is increased. Therefore leaving a stent for longer time may enlarge the lumen with improvement of epiphora.
  2. Stent straightens various bends in the canaliculi causing better flow through these narrow conduits.
Clinical conditions/ Indications of use
  1. Punctum and/or canalicular stenosis- Stent mechanically dilates the punctum and vertical canaliculus, restores normal tear outflow and prevents re-stenosis. Complete obstruction of the canaliculus may require trephination with Sisler’s lacrimal trephine before stent placement.
  2. Traumatic canalicular laceration/tear- Stents not only provides internal ‘mechanical support’ to the canalicular wall and surrounding soft tissue but also helps in the ‘directional’ canalicular epithelium growth by providing ‘the scaffold’ which is vital for a tract to stay patent. This can provide anatomically patent and functional lacrimal passages.
  3. Congenital nasolacrimal duct obstruction (CNLDO) – In case primary probing fails, intubation with stents can be considered as a good option as it has been shown to be effective in 84% children in PEDIG study.[16] This is especially useful in cases with canalicular stenosis, presaccal/postsaccal stenosis, and diffuse narrowing of NLD. It is a viable option to be considered in above situations before considering for dacryocystorhinostomy (DCR).
  4. To maintain the internal canalicular opening (ICO) and ostium patency after DCR- Although an issue of dispute, its use in cases with high risk of surgical failure (ICO membranes, young patients etc.) is advocated as the ostium closure is the most common cause of failure in DCR surgery. The role of intubation becomes important to prevent the ostium closure and to convey the dynamicity of the muscle action to the internal ostium. Hence it maintains the anatomic and functional patency of internal DCR ostium. It also helps to negate the inadvertent canalicular trauma while probing and manipulating canaliculi, intraoperatively.
  5. Special situations such as repeat  DCR, young age, small/fibrosed sac, inadvertent damage to sac during surgery, inadequate/small sac flaps or nasal mucosal flaps, history of acute dacryocystitis and certain systemic conditions (Wegener’s granulomatosis etc.) warrants the use of stents to prevents closure of ostium.
  6. Functional epiphora- Is defined as epiphora when lacrimal passages are anatomically patent (on irrigation) with absence of ocular or adnexal abnormality. Intubation in these cases increases the outflow, keeps the passages in dilated state and with improvement of symptoms.[17]
Types of lacrimal stents or intubation systems

The lacrimal intubation devices or stents can be classified grossly into monocanalicular and bicanalicular stents (Table 1). The monocanalicular stents usually traverse a single canaliculus to lacrimal sac and NLD but the bicanalicular stents pass through both canaliculi into the sac and nasal cavity and are tied in a loop fashion inside the nasal cavity. Sometimes, the loop may traverse only the canaliculi via common canaliculus (Marube’s technique). Morphologically, the working ends of bicanalicular silicone lacrimal intubation sets have a metallic probe like rod (bodkin) which is malleable enough to be pulled out via inferior meatus externally. It can be done with a rigid nasal endoscope under visualization or else ‘metal to metal touch’ with the tip of a hook or Kelly’s curved artery forceps. The silicone stents are available in 23, 25 and 27 gauge sizes and are used according to the age of patient and condition of canaliculus.
 
Monocanalicular lacrimal intubation devices

A.    MonokaTM stent

The Monoka (Mono=single, ka=canalicular) is a silicone stent having different lengths for children and adults. It has a metallic bodkin or blue/black coloured monofilament thread at its distal working end which helps in its easier passage through narrow conduits. A special “punctal fixation device” (PFD) is present at its proximal end which consist of an oval collarette (3-4mm), vertical hollow tube (2mm) and a horizontal bulb at vertical and horizontal tubes junction. The wide collarette sits atop the punctum non-traumatically, prevents its canalicular migration, helps during tube removal and is the only structure visible externally once the stent is in-situ. The horizontal bulb snugly fits or anchors the stent at ampulla making it a self-retaining type. The silicone stent has an external diameter of 0.64 mm with 80 mm long and 0.8mm wide metal bodkin (Figure 1a). The lumen (0.3mm) of collarette is used for its easier and safe insertion with the help of a special plug inserter or even punctum dilator can be used.

The less popular ‘self threading’ Ritleng variant of Monoka stent has got a black and stout ‘poly-ethylene-ether-ketone’ (PEEK) thread at its end. The hollow stent end is swaged over the PEEK thread which can be detached after intubation (Figure 1b). Monoka stent was invented in 1988 by Fayet and co-workers who showed a success rate similar to that of the bicanalicular stents.[19] Kaufman and Goldstein et al achieved good success rate (79% and 93% respectively) in terms of patent canaliculus.[20,21]

B.    Mini-MonokaTM stent

This is a smaller variant of Monoka stent and is used mainly for proximal lacrimal system (punctum and canaliculus) intubation. It is 30 mm long, self retaining silicone stent with similar width and narrower PFD (Figure 2). Various studies have established its efficacious role in management of canalicular lacerations while the recent literature reports its potential use in punctal and canalicular stenosis or obstructions as well. Theoretically, for ensuring its in-situ retention, the length of stent should be generally >10 mm as this places the cut end beyond the common canaliculus into the sac.


C.    Monoka-Crawford stent

This is a modification of Monoka stent created by attaching a Crawford type (olive tip) metallic bodkin to its working end (Figure 3). The olive tip of bodkin assures non-traumatic passage through canaliculi and NLD along with easy endonasal retrieval with a specially designed Crawford hook which engages the olive tip in nasal cavity.  The stent is pulled gently without damaging the nasal mucosa, turbinate and floor of nose. The dimensions of silicone stent are same as that of standard Monoka.


D.    MasterkaTM stent (pushed Monoka)

This is a novel preloaded silicone intubation stent designed by Dr.Bruno Fayet for canalicular and nasolacrimal duct intubation. MasterkaTM is available in three lengths (30, 35 and 40 mm) and has a similar proximal PFD as regular Monoka. It is hollow tube throughout its length with an outer diameter of 0.96 mm. It is pre-mounted over a thin metallic stylet or guidewire and provides the desired stoutness inside the narrow tracts (Figure 4).  A separate marked probe is available to measure the length of the stent needed (Figure 4 a). After punctal dilatation, the stent is introduced in a similar way as the routine probing is performed. After endoscopically ensuring its tip in inferior meatus, the metallic stylet/guidewire is pulled out while keeping the silicone stent in place (Figure 5). The manufacturers compare this stent to ‘venous catheters’ in which the guidewire could be possibly removed and reinserted without altering the stability and shape of the prior placed stent. The metallic stylet provides better stability, control and manoeuvrability of the stent hence making it useful for stenosed lacrimal system pathways.













E.    Disposable Punctum Dilator and Plug Inserter

It has a polypropylene body with two polypropylene compressible flanges and a stainless steel tip which acts as a punctum dilator (Figure 6). After stent insertion, the steel tip is inserted into the hole of collarette and the PFD is pushed into its position. The flanges are then compressed which pushes the PFD out keeping the stent stable in-situ. It simplifies the insertion process which can be cumbersome or damaging to the collarette if performed with a toothed forceps or other instrument. This device is a very helpful tool for the beginners to handle the stent properly.



Bicanalicular lacrimal intubation devices

A.    Crawford stents

It uses a silicone stent which is swaged onto 2 malleable steel bodkins (0.4-0.6mm diameter) at both of its ends. Both steel bodkins have olive shaped bulbous tips of 1mm diameter end for its easier, atraumatic passage and retrieval with Crawford hook under visualisation (Figure 7). The metallic rods are then detached and 2-3 square knots are tied before cutting. The Crawford- II intubation device has wider diameter silicone of 0.93mm. Occasionally, the olive tip can make the passage of the bodkin difficult via stenosed or narrow tracts.



B.    Ritleng intubation device

It consists of a hollow, stainless steel probe which is passed through the canaliculi and NLD till its tip is visible in inferior meatus, endoscopically. The probe has a funnel-shaped proximal entrance, a flat guide disc for orientation and a narrow slit like opening, 2-5 mm proximal to the tip, which can be directed anteriorly as the guide disc is rotated. The external diameter of probe is 1-2 mm and the lumen is 0.5-1mm wide (Figure 8). Ritleng intubation consist of a stout prolene monofilament (0.2-0.4 mm diameter) thread composed of a thicker dark blue initial portion followed by a thinner light blue segment. The silicone stent which can be a self retaining Monoka stent (0.64mm diameter) is attached to prolene. Once the prolene is identified in inferior meatus, it is pulled out generously and the probe is taken out of lacrimal system. Silicone stent is then detached and probe is taken out. For second canaliculus similar steps are repeated.




C.    O’Donoghue, Guboir and Bika (bicanalicular) stents

These all are different variants of bicanalicular silicone intubation device available in different parts of world. There are slight modifications in the design of metallic probes or tips (Figure 9). The Bika type has got straight tips like a Bowman’s probe and need a firm grip while taking out from nose. The thickness or gauge of silicone stent can vary from [20,23] (adults) and 27 (pediatric).





D.    Self-retaining bicanalicular stents

Designed by P.Bige`, it is the latest innovation in the field as these silicone stent segments traverse both canaliculi till the lacrimal sac. Each end of this semicircular device has 2 stout angulated wings/flanges which pose no resistance while proceeding forward into the canaliculus, but once they get into open cavity (lacrimal sac), the flanges open up and give resistance to their removal against the common canalicular opening (Figure 10).

It is available in different lengths of 25, 30 and 35 mm with a disposable sizer. Both limbs are pushed through possible stenosed canaliculi and all the four flanges open at the internal punctum opening, hence keeping it in place.

Timing of stent removal

The debate for using the stent and the timing of stent removal still exists in literature. Earlier it was suggested that the stents should be kept at least for 3-6 months in-situ. However concepts are now changing and recent literature advocates stent removal at 4-6 weeks after a DCR surgery. This is because that by this period ostium healing is complete and if kept longer stent may cause granuloma formation around ostium.[22] For the indications like punctal stenosis, canalicular stenosis/obstruction, canalicular laceration and canalicular trephination, is still preferable to keep stent for at least 3 months.

Complications of lacrimal stents
  1. Stent prolapse or loss: needs repositioning or replacement. Nasal endoscopy allows direct visualization and makes it easier to perform.
  2. Punctal slitting or cheese wiring: due to excessive bicanalicular stent loop tightening or inferior pull.
  3. Punctal/ostium granuloma formation with prolonged intubation.
  4. Secondary bacterial/fungal infections.
  5. Rare: conjunctival or corneal erosions/ infections
Conclusion

Lacrimal intubation is indicated in punctal or canalicular stenosis/obstruction after successful recanalization procedure. It helps to restore normal epithelial lining and prevents re-closure. Its role in primary DCR is still debatable but it appears to increase the success rates in complicated/repeat DCR. A thorough knowledge about the mechanism and design of stent is essential in choosing the appropriate model.

Cite This Article as: Singh M, Kamal S, Sowmya V. Lacrimal stents and intubation systems: An insight. Delhi J Ophthalmol 2015;26:14-9.

Acknowledgements: None

Conflict of interest: None

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  17. Shams PN, Chen PG, Wormald PJ, Sloan B, Wilcsek G, McNab A, Selva D. Management of functional epiphora in patients with an anatomically patent dacryocystorhinostomy. JAMA Ophthalmol 2014; 132:1127-32.
  18. Fayet B, Katowitz WR, Racy E, Ruban JM, Katowitz JA. Pushed monocanalicular intubation: an alternative stenting system for the management of congenital nasolacrimal duct obstructions. JAAPOS 2012; 16:468-72.
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Singh M, Kamal S, Sowmya VLacrimal Stents and Intubation Systems: An Insight.DJO 2015;26:14-19
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Singh M, Kamal S, Sowmya VLacrimal Stents and Intubation Systems: An Insight.DJO [serial online] 2015[cited 2018 Nov 17];26:14-19. Available from: http://www.djo.org.in/articles/26/1/lacrimal-stents-and-intubation.html
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