Nasolacrimal Duct Obstruction, Congenital

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Article initiated by:
Katherine A. Lee M.D., Ph.D
All contributors:
Brad H. Feldman, M.D., Aaron M. Miller, MD, MBA, FAAP, Katherine A. Lee M.D., Ph.D, Alex Kozak, Anand Kumar, MS, K. David Epley, M.D., Jill Rotruck, MD, S. Grace Prakalapakorn, MD, MPH, Michael T Yen, MD, Marcus M. Marcet, MD, Dylan Griffiths, Cat Nguyen Burkat, MD FACS
Assigned editor:
Jill Rotruck, MD, Anne Barmettler, MD
Review:
Assigned status Up to Date
 by Michael T Yen, MD on September 15, 2024.


Disease Entity

Nasolacrimal duct obstruction is a blockage of the lacrimal drainage system. In children the majority of nasolacrimal duct obstruction is congenital. The blockage occurs most commonly at the distal end of the duct.

Epidemiology

Cogenital nasolacrimal duct obstruction occurs in up to 11% of normal newborn infants.[1] There is no sex predilation and no genetic predisposition.

Disease

Congenital nasolacrimal duct obstruction occurs in approximately 5% of normal newborn infants. The blockage occurs most commonly at the valve of Hasner at the distal end of the duct. There is no sex predilection and no genetic predisposition. The blockage can be unilateral or bilateral.

Etiology

The etiology of congenital nasolacrimal duct obstruction is most commonly a membranous obstruction at the valve of Hasner at the distal end of the nasolacrimal duct that has delayed involution. Other etiologies include general stenosis of the duct or bony abnormalities with narrow inferior nasolacrimal canal, which is more common in patients with midfacial abnormalities. Congenital proximal lacrimal outflow dysgenesis involves Maldevelopment of the punctum and canaliculus (congenital proximal lacrimal outflow dysgenesis) or stenosis of the inferior meatus  can occur concurrently with distal obstruction. Dacryocele, which is a congenital blockage of the nasolacrimal duct with distention of the nasolacrimal sac, is addressed separately.

Congenital dacryocystocele.jpg

Risk Factors

Children who are born prematurely or with Down syndrome, craniosynostosis, Goldenhar sequence, clefting syndromes, hemifacial microsomia, or any midline facial anomaly are at an increased risk for congenital nasolacrimal duct obstruction.

Natural History

The rate of spontaneous resolution is estimated to be 90% within the first year of life.[2][3][4] The rate of spontaneous resolution is 44-76% between 12 and 24 months and may still occur even after 24 months.[5][6]

Diagnosis

Signs and Symptoms

A history of tearing, mucous discharge and epiphora of one or both eyes is typical with concordant increased tear lake, mucous or mucopurulent discharge, and epiphora found on exam. . When pressure is applied over the lacrimal sac, there may be reflux of mucoid or mucopurulent material from the punctum. The periocular skin may be chapped from continual exposure to tears and discharge. Proximal lacrimal outflow blockage or dysgenesis tends to present with an increased tear lake and epiphora without mattering. The globe is usually white. The signs and symptoms are usually worse with a concurrent upper respiratory infection.  

Diagnostic procedures

A fluorescein dye disappearance test can be helpful in confirming the diagnosis of nasolacrimal duct obstruction.[7] A drop of fluorescein is instilled into the eyes or introduced on a moistened pledget. The disappearance of dye from the tear film after 5 minutes is observed. Retained dye in a thickened tear strip is diagnostic of an obstruction. The test is most useful if the disease is unilateral and the findings of the affected eye can be compared to those of the normal eye.

Differential diagnosis

The differential diagnosis of nasolacrimal duct obstruction includes acquired nasolacrimal duct obstruction (as can occur following trauma, viral conjucntivitis, acute dacryocystitis, and topical antiviral medications), acute conjunctivitis, glaucoma, congenital anomalies of the upper lacrimal drainage system (punctal or canalicular atresia or agenesis), entropion, epiblepharon, triachiasis, dacryocele, obstruction of the inferiro meatus due to nasal structures (structural or functional).

Sequelae

Congenital nasolacrimal duct obstruction is a risk factor for amblyopia and anisometropia.[6][8] Anisometropia is more common in unilateral compared to bilateral cases.[8] Associated preseptal cellulitis or dacryocystitis can occur, although rarely. Obstruction can be secondary to a dacryocele, for which curative treatment is much more pressing than for congenital nasolacrimal duct obstruction.

Management

General treatment

Treatment of congenital lacrimal duct obstruction consists of initial observation for resolution followed by probing of children with persistent duct obstruction. Probing failures are treated with more aggressive surgical procedures including balloon dacryoplasty and nasolacrimal duct intubation. Endoscopic dacryocystorhinostomy is generally reserved for intubation and balloon dacryoplasty failures.

Medical therapy

Medical management of nasolacrimal duct obstruction consists primarily of observation, lacrimal massage, and treatment with topical antibiotics for secondary infection. The efficacy of lacrimal massage in relieving duct obstruction is not well established. Kushner reported that lacrimal massage performed with occlusion of the common canaliculus and firm downward pressure on the lacrimal sac was more effective than gentle lacrimal massage or no massage.[9] Dacryocystitis in association with neonatal nasolacrimal duct obstruction should be treated with systemic antibiotics and urgent probing of the nasolacrimal duct with attention to the need to marsupialize the membranous cyst at the distal end of the duct.

Medical follow up

Primary care doctors are usually the first medical providers to treat nasolacrimal duct obstruction. Frequently infants are referred to the ophthalmologist for surgical treatment only after a period of nonresolution. The age of the infant at referral depends on the preference of the primary care physician and also on his knowledge of the surgical practice of the ophthalmologist in regard to nasolacrimal duct probing. An ophthalmologist who performs in office probing procedures will often offer probing to families of infants 6 months to <10 months. In contrast, the ophthalmologist who performs probings under general anesthesia or conscious sedation might wait until the infant is older because of the reluctance of families to have their infant undergo general anesthesia and to allow full chance for the obstruction to spontaneously clear.

Surgery

Primary treatment of nasolacrimal duct obstruction consists of nasolacrimal duct probing. In this procedure a probe ranging in size from 0.70 to 1.10 mm in diameter is passed through either the upper or lower punctum following dilation of the punctum. The probe is advance along the canaliculus while exerting gentle lateral traction on the lid until it reaches the nasal bone. Then the probe is rotated 90 degrees and gently introduced into the nasolacrimal duct and advanced into the nose.

During probing a gritty feeling can be felt along a stenotic duct and if there is a distal membrane, a distinct "pop" can be felt as the membrane is breached. If the probing is performed under general anesthesia, the inferior turbinate can be infractured medially to open the area underneath it.

Nasolacrimal duct patency can be confirmed several ways:

  1. The distal end of the probe in the nose can be palpated with another probe, achieving metal-on-metal contact.
  2. A small bolus of saline can be irrigated through the duct. If the infant is awake, the bolus will illicit a swallowing reflex. If the child is anesthetized the saline (colored with fluoroscein typically) can be aspirated with suction.
  3. The end of the probe can sometimes be directly observed. Studies of primary surgical management have found probing to be successful in 70%–97% of cases, with many reports around 90%.[10][11][12][13][14][15]

The success of simple probing declines slightly with the increasing age of the child. Several investigators have reported a drop off in probing success rate with increased age, generally after 24 to 36 months.[16][17][18][19]

A prospective observational study of primary nasolacrimal duct probing in infants 6 to 60 months of age by the Pediatric Eye Disease Investigator Group showed an overall success rate of 78% with no decline in the efficacy of simple nasolacrimal duct probing through 36 months of age.[20] Robb has reported > 90% success rates with initial probing beyond 36 months of age.[21] The success of simple probing is less for bilateral obstructions. Complex obstructions in the proximal part of the duct have a poorer success rate following probing than simple membranous obstructions at the end of the duct. The location of nasolacrimal duct probing- in office versus in a facility under sedation has been controversial with some physicians strongly advocating in office probing for its ease of performance and avoidance of general anesthesia. Others tout the small but significant risk of aspiration during the in-office procedure and state that, since in-office probing is generally performed in children less than 12 months of age, children who would resolve spontaneously are treated unnecessarily. In its observational series, the PEDIG investigators found a slightly decreased success rate for in office (72%) as compared to in facility (80%) probings in children less than 12 months of age.[20]Repeat nasolacrimal duct probing is generally not a successful procedure with reported success rates of 40-60%.[18][22][23]

Nasolacrimal duct stent insertion

Nasolacrimal duct stent insertion is used as a primary procedure or following failure of simple probing. The procedure involves nasolacrimal duct probing followed by the passage of a nasolacrimal duct probe that has a stent swedged to one end. Bicanalicular stents have two probes with an intervening stent. One probe is passed through the upper punctum and the other through the lower punctum. The probes are removed and the free ends of the stent are tied in the nose and sometimes secured with a suture. Monocanalicular stents have a plug that is seated at the upper or lower puntum while the stent hangs freely in the nose. The success of nasolacrimal duct stent insertion as a primary procedure is estimated to be between 79 to 96%.[24][25][26][27]

There is no difference in success rate for primary stent insertions between monocanalicular and bicanalicular stents.[27]Stents are left in place for a variable period time. Migliori and Putterman had 100% resolution in 38 patients whose stents were removed at 6 weeks.[28]PEDIG investigators found a deceased success rate for stent removed less than 2 months after insertion.[29]Nasolacrimal duct stent insertion is often performed following a failed probing procedure with reported success rates of 66-100%.[30][31][32][28][33][34][35][36][37][38][39][40]

In a prospective observational study of 88 eyes undergoing stent insertion following failed probing, PEDIG found a success rate of 84% in relieving all three clinical signs of duct obstruction: epiphora, mucous discharge and increased tear lake.[29]

Balloon catheter dilation

Balloon catheter dilation can be used as a primary procedure or following failure of a simple probing. Standard nasolacrimal duct probing is followed by the introduction of a LacriCath balloon catheter (Atrion Medical, Birmingham, Alabama) into the duct. The balloon is inflated according to the manufacturer's specifications and withdrawn. Success of balloon catheter dilation as a primary or secondary procedure has been estimated between 53 and 95%. Cost of the materials is also a consideration. [41][42][43][44][45][46]

A retrospective comparison between balloon catheter dilation and simple probing as a primary procedure for treatment of nasolacrimal duct obstruction showed no treatment advantage for balloon catheter dilation. [46]

Nasal endoscopy is sometimes used in conjunction with probing, stent insertion and balloon catheter dilation in the treatment of persistent nasolacrimal duct obstruction. It is also frequently used in the treatment of congenital dacryocystoceles to identify and marsupialize the intranasal cyst.[47][48][49][50][51]In a prospective evaluation of the incidence of intranasal abnormalities in infants with mucoceles, Lueder found intranasal cysts in 22 of 22 infants examined.[47] In children who failed prior nasolacrimal duct probing and in children >18 months of age at first treatment, intranasal abnormalities were identified in 8.5 and 6% respectively, most commonly nasolacrimal duct cysts, redundant nasal mucosa and distal membranes. A membranous flap covering the distal duct ostium can be identified and removed with visualization. [47] Gardiner et al found no increased benefit for repeat nasolacrimal duct probing combined with endoscopy and correction of intranasal abnormalities when compared to stent insertion following a failed probe without nasal endoscopy.[52] However, other authors have advocated routine use of endoscopy for nasolacrimal duct probing as occasionally there may be a membranous tissue flap that should be removed from over the intranasal ostium to avoid failure after routine probing and stunting.

Dacryocystorhinostomy (DCR)

DCR can be performed from either an external or endoscopic approach. The procedure is generally reserved for children who have failed other procedures. External DCR has a reportedly excellent success rate in children (96%).[53]

Endoscopic dacryocystorhinostomy has success rate approaching that of external DCR in children (82-94%). [54][55][56] The endoscopic approach is preferred by most pediatric ophthalmologists because there is no external scar, the medial canthus is not disrupted, and nasal endoscopy can help identify intranasal abnormalities that can be rectified at the time of surgery. The use of adjunctive mitomycin C at the osteomy site in endoscopic DCR has been reported to be safe and effective in children, though is typically not necessary.[57] A light pipe can be used to facilitate identification of the nasolacrimal duct sac.

Surgical follow up

Surgical follow up after probing can be by office visit or phone contact. Because the success rate of probing is high and parents are familiar with the signs and symptoms of an unresolved obstruction, office follow up is often left on an as needed basis.

Follow up after nasolacrimal duct stent insertion and dacryocystorhinostomy depends on how long the stents are intended to be left in place. Most stents can be removed in the office. Monocanalicular stents are particularly easy to remove in the office.

Complications

  • Complications following nasolacrimal duct probing include nasal bleeding, restenosis of the duct and creation of a false passage of the duct.
  • Complications following stent insertion include the above plus early loss of stents.
  • Complications of DCR include the above plus reclosure of the surgically created osteomy.

Prognosis

The prognosis for resolution of nasolacrimal duct obstruction by one or more surgical procedures is quite good. The success rate of simple probing is excellent. There is a higher rate of recurrence in patients who are treated at age 3 years or older and patients with chronic rhinitis. Children with conditions that increase their risk of probing failure have a poorer prognosis but can often be successfully treated with additional procedures.

Additional Resources

References

  1. ↑ Sathiamoorthi S, Frank RD, Mohney BG. Incidence and clinical characteristics of congenital nasolacrimal duct obstruction. Br J Ophthalmol. 2019 Apr;103(4):527-529. doi: 10.1136/bjophthalmol-2018-312074. Epub 2018 Jun 6. PMID: 29875230; PMCID: PMC7004273.
  2. ↑ Paul TO. Medical management of congenital nasolacrimal duct obstruction. J Pediatr Ophthalmol and Strabismus. 1985; 22:68-70.
  3. ↑ Nelson, LB, Calhoun, JH, Menduke, H. Medical management of congenital nasolacrimal duct obstruction.Ophthalmology. 1985; 92:1187-1190.
  4. ↑ Petersen, RA, Robb, RM. The natural history of congenital obstruction of the nasolacrimal duct. J Pediatr Ophthalmol and Strabismus. 1978; 15:246-250.
  5. ↑ Young JD, MacEwen CJ, Ogston SA. Congenital nasolacrimal duct obstruction in the second year of life: a multicentre trial of management. Eye (Lond). 1996;10 ( Pt 4):485-91. doi: 10.1038/eye.1996.107. PMID: 8944104.
  6. ↑ 6.0 6.1 Sims DT, Gillette TB, Lam JG, Liu D, Lee C, Ding L, Tarczy-Hornoch K, Cabrera MT. Anisometropia and Amblyopia Outcomes in Early Versus Late Resolution of Congenital Nasolacrimal Duct Obstruction in Older Infants. Ophthalmic Plast Reconstr Surg. 2024 Jan-Feb 01;40(1):39-42. doi: 10.1097/IOP.0000000000002496. Epub 2023 Sep 1. PMID: 38241617; PMCID: PMC10799212.
  7. ↑ MacEwen, CJ, Young, JDH. The fluorescein disappearance test (FDT): an evaluation of its use in infants. J Pediatr Ophthalmol and Strabismus. 1991; 28:302-305.
  8. ↑ 8.0 8.1 Hareendran H, Allapitchai F, Ravindran M, Shukul K, Rengappa R. Anisometropia and refractive status in children with congenital nasolacrimal duct obstruction-a prospective observational study. J AAPOS. 2022 Apr;26(2):76.e1-76.e4. doi: 10.1016/j.jaapos.2021.11.015. Epub 2022 Mar 18. PMID: 35314316.
  9. ↑ Kushner, Burton J. Congenital Nasolacrimal System Obstruction. Arch Ophthalmol. 1982;100:597-600.
  10. ↑ Robb RM. Success rates of nasolacrimal duct probing at time intervals after 1 year of age. Ophthalmology 1998;105:1307–9.
  11. ↑ Ciftci F, Akman A, Sonmez M, et al. Systematic, combinedtreatment approach to nasolacrimal duct obstruction in different age groups. Eur J Ophthalmol 2000;10:324 –9.
  12. ↑ Casady DR, Meyer DR, Simon JW, et al. Stepwise treatment paradigm for congenital nasolacrimal duct obstruction. Ophthal Plast Reconstr Surg 2006;22:243–7.
  13. ↑ Baker JD. Treatment of congenital nasolacrimal system obstruction. J Pediatr Ophthalmol Strabismus 1985;22:34–6.
  14. ↑ Katowitz JA, Welsh MG. Timing of initial probing and irrigation in congenital nasolacrimal duct obstruction.Ophthalmology 1987;94:698-705.
  15. ↑ Stager D, Baker JD, Frey T, et al. Office probing of congenital nasolacrimal duct obstruction.Ophthalmic Surg 1992;23:482–4.
  16. ↑ Kashkouli MB, Beigi B, Parvaresh MM, Kassaee A, Tabatabaee Z. Late and very late initial probing for congenital nasolacrimal duct obstruction: What is the cause of failure? Br J Ophthalmol 2003;87:1151-3.
  17. ↑ Honavar,SG, Prakash, VE, Rao, GN. Outcome of Probing for Congenital Nasolacrimal Duct Obstruction in Older Children. Am J Ophthalmol 2000;130:42–48.
  18. ↑ 18.0 18.1 Katowitz, JA, Welsh, MG. Timing of initial probing and irrigation in congenital nasolacrimal duct obstruction. Ophthalmology. 1987; 94:698-705.
  19. ↑ Mannor, GE, Rose, GE, Frimpong-Ansah, K, Ezra, E. Factors affecting the success of nasolacrimal duct probing fro congenital nasolacrimal duct obstruction. Am J Ophthalmol. 1999;127:616-617.
  20. ↑ 20.0 20.1 Pediatric Eye Disease Investigator Group. Primary treatment of nasolacrimal duct obstruction with probing in children younger than 4 years. Ophthalmology. 2008;115:577–584.
  21. ↑ Robb, Richard. Success rates of nasolacrimal duct probing at time intervals after 1 year of age. Ophthalmology. 1998; 105:1307-1310.
  22. ↑ Pediatric Eye Disease Investigator Group. Repeat probing for treatment of persistent nasolacrimal duct obstruction. J AAPOS. 2009;13:306-307.
  23. ↑ Stager D, Baker JD, Frey T, Weakley DR, Birch EE. Office probing of congenital nasolacrimal duct obstruction. Ophthalmic Surgery. 1992;23: 482-484
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  25. ↑ Kaufman LM, Guay-Bhatia LA. Monocanalicular intubation with Monoka tubes for the treatment of congenital nasolacrimal duct obstruction. Ophthalmology 1998;105:336-41.
  26. ↑ Engel JM, Hichie-Schmidt C, Khammar A, Ostfeld BM, Vyas A, Ticho BH. Monocanalicular silastic intubation for the initial correction of congenital nasolacrimal duct obstruction. J AAPOS 2007;11:183-6.
  27. ↑ 27.0 27.1 Pediatric Eye Disease Investigator Group. Primary treatment of nasolacrimal duct obstruction with nasolacrimal duct intubation in children younger than 4 years of age. J AAPOS. 2008;12:445-450.
  28. ↑ 28.0 28.1 Migliori ME, Putterman AM. Silicone intubation for the treatment of congenital lacrimal duct obstruction: successful results removing the tubes after six weeks. Ophthalmology 1988;95:792–5. [PubMed: 3211482]
  29. ↑ 29.0 29.1 Pediatric Eye Disease Investigator Group. Balloon Catheter Dilation and Nasolacrimal Intubation for Treatment of Nasolacrimal Duct Obstruction Following a Failed Probing. Arch Ophthalmol. 2009; 127: 633–639
  30. ↑ Dortzbach RK, France TD, Kushner BJ, Gonnering RS. Silicone intubation for obstruction of the nasolacrimal duct in children. Am J Ophthalmol 1982;94:585–90. [PubMed: 7148939]
  31. ↑ Pashby RC, Rathbun JE. Silicone tube intubation of the lacrimal drainage system. Arch Ophthalmol 1979;97:1318–22. [PubMed: 454271]
  32. ↑ Durso F, Hand SI Jr, Ellis FD, Helveston EM. Silicone intubation in children with nasolacrimal obstruction. J Pediatr Ophthalmol Strabismus 1980;17:389–93. [PubMed: 7205521]
  33. ↑ Leone CR Jr, Van Gemert JV. The success rate of silicone intubation in congenital lacrimal obstruction. Ophthalmic Surg 1990;21:90–2. [PubMed: 2330203]
  34. ↑ Heirbaut AM, Colla B, Missotten L. Silicone intubation for congenital obstruction of nasolacrimal ducts. Bull Soc Belge Ophtalmol 1990;238:87–93. [PubMed: 2131128]
  35. ↑ Beigi B, O’keefe M. Results of Crawford tube intubation in children. Acta Ophthalmol (Copenh) 1993;71:405–7. [PubMed: 8362644]
  36. ↑ Al-Hussain H, Nasr AM. Silastic intubation in congenital nasolacrimal duct obstruction: a study of 129 eyes. Ophthal Plast Reconstr Surg 1993;9:32–7.
  37. ↑ Aggarwal RK, Misson GP, Donaldson I, Willshaw HE. The role of nasolacrimal intubation in the management of childhood epiphora. Eye 1993;7:760–2. [PubMed: 8119427]
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  39. ↑ Lim CS, Martin F, Beckenham T, Cumming RG. Nasolacrimal duct obstruction in children: outcome of intubation. J AAPOS 2004;8:466–72. [PubMed: 15492741]
  40. ↑ Pe MR, Langford JD, Linberg JV, et al. Ritleng intubation system for treatment of congenital nasolacrimal duct obstruction. Arch Ophthalmol 1998;116:387–91. [PubMed: 9514499]
  41. ↑ Tao S, Meyer DR, Simon JW, Zobal-Ratner J. Success of balloon catheter dilatation as a primary or secondary procedure for congenital nasolacrimal duct obstruction. Ophthalmology 2002;109:2108–11. [PubMed: 12414423]
  42. ↑ Becker BB, Berry FD, Koller H. Balloon catheter dilatation for treatment of congenital nasolacrimal duct obstruction. Am J Ophthalmol. 1996;121:304–9. [PubMed: 8597274].
  43. ↑ Hutcheson KA, Drack AV, Lambert SR. Balloon dilatation for treatment of resistant nasolacrimal duct obstruction. J AAPOS 1997;1:241–4. [PubMed: 10532771]
  44. ↑ Tien D, Young D. Balloon dilation of the nasolacrimal duct. J AAPOS 2005;9:465–7. [PubMed:16213397]
  45. ↑ Pediatric Eye Disease Investigator Group. Primary treatment of nasolacrimal duct obstruction with balloon catheter dilation in children younger than 4 years of age. J AAPOS. 2008;12:451-455.
  46. ↑ 46.0 46.1 Gunton KB, Chung CW, Schnall BM, Prieto D, Wexler A, Koller HP. Comparison of balloon dacryocystoplasty to probing as the primary treatment of congenital nasolacrimal duct obstruction. J AAPOS. 2001;5:139-142.
  47. ↑ 47.0 47.1 47.2 Lueder GT. Endoscopic treatment of intranasal abnormalities associated with nasolacrimal duct obstruction. J AAPOS. 2004;8: 128-132.
  48. ↑ Thomas SA, Drack AV, Sands RE, Yoon P, Friedman NR, Chan, K. Clinical and Histopathologic Features of Congenital Dacryocystoceles Associated with Intranasal Cysts. JAAPOS 2000;4:46-53.
  49. ↑ Lueder, GT. Neonatal dacryocystitis associated with nasolacrimal duct cysts. J Pediatr Ophthalmol Strabismus. 1995;32:102-106.
  50. ↑ Wong JF, Woog JJ, Cunningham MJ, Rubin PAD, Curtin HD, Carter BL. A multidisciplinary approach to atypical lacrimal obstruction in childhood. Ophthalmic Plastic and Reconstructive Surg. 1999; 15:293-298.
  51. ↑ Cunningham MJ, Woog JJ. Endonasal endoscopic dacryocystorhinostomy in children. Arch Otolaryngol Head Neck Surg. 1998;124:328-333.
  52. ↑ Barnes EA, Abou-Rayyah Y, Rose GE. Pediatric dacryocystorhinostomy for nasolacrimal duct obstruction. Ophthalmology 2001; 108:1562-1564.
  53. ↑ Gardiner, JA, FRCSC,Forte, V, Pashby, RC, Levin, AV. The role of nasal endoscopy in repeat pediatric nasolacrimal duct probings. J AAPOS. 2001;5:148-52.
  54. ↑ VanverVeen DK, Jones DT, Tan H, Petersen RA. Endoscopic dacryocystorhinosotmy in children. J AAPOS. 2001;5:143-47.
  55. ↑ Komınek P, Cervenka S. Pediatric Endonasal Dacryocystorhinostomy: A Report of 34 Cases. The Laryngoscope. 2005; 115:1800–1803.
  56. ↑ Komınek P, Cervenka S, Matousek P, Pniak T, Zelenik Z. Primary pediatric endonasal dacryocystorhinostomy- a review of 58 procedures. Int J Ped Otorhinolaryngology. 2010; 74: 661-664.
  57. ↑ Dolmetsch AM, Gallon MA, Holds JB. Nonlaser endoscopic endonasal dacryocystorhinostomy with adjunctive mitomycin C in children. Ophthalmic Plastic and Reconstructive Surg. 2008;24:390–393
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