Evaluation of Polyurethane Nasolacrimal Duct Stents: In Vivo Studies in New Zealand Rabbits

Scanning electron microscopic features of lacrimal drainage silastic stents: Comparison of various Crawford and large-diameter stents

PURPOSE

This study aimed to examine the differences in the biofilms and physical deposits on Crawford stents compared to large-diameter stents.

METHODS

A prospective interventional study was performed on a series of patients undergoing external or endoscopic dacryocystorhinostomy (DCR) and endoluminal lacrimal duct recanalization (ELDR) with either Crawford or large-diameter stents. All the Crawford stents were retrieved at six weeks and the large-diameter ones at eight weeks following the surgical intervention. There was no evidence of post-operative infection in any of the patients. Following extubation, standard protocols of scanning electron microscopy were used to assess the biofilms and physical deposits on the stents.

RESULTS

A total of 15 stents were studied. Of these, twelve were Crawford, and three were large-diameter stents. The Crawford stents were from two different manufacturers. All the stents demonstrated evidence of biofilm formation and physical deposits. The Crawford stents showed thin biofilms and sparse physical deposits, but there were no demonstrable differences amongst stents from different manufacturers. However, the deposits and biofilms were thicker and more extensive in the large-diameter stents than the Crawford ones. The biofilms from all stents showed the presence of polymicrobial communities within the exopolysaccharide matrix.

CONCLUSIONS

The present study found differences in biofilms and physical deposits between Crawford and large-diameter stents. These differences can be partly explained by stent duration, size, and their tissue interactions.

Effect of Topical 5-Fluorouracil on Lacrimal Drainage System: Histopathological Evidence From Animal Experiments and Potential Clinical Implications

PURPOSE

The purpose of this study is to investigate the histopathological changes in the lacrimal drainage system of rabbits following the application of 1% topical 5-fluorouracil (5-FU) for 4 weeks.

METHODS

Ten eyes of 10 healthy New Zealand white rabbits were subjected to topical instillation of 1% (10 mg/mL) 5-FU, 1 drop 4 times a day for 4 weeks. Rabbits underwent a detailed ocular examination including eyelids, ocular surface, punctal, peri-punctal changes, and nasolacrimal duct patency at baseline and after 4 weeks of 5-FU. The rabbits were then sacrificed, and the eyelid, conjunctiva, lacrimal gland, and the entire lacrimal drainage system were retrieved for histopathological analysis as per standard protocols.

RESULTS

Clinically demonstrable peripunctal changes and canalicular stenosis were noted in 6 (60%, 6/10) rabbits. Two of these (20%, 2/10) had additional complete regurgitation of clear fluid, indicating a nasolacrimal duct obstruction. The remaining 4 (40%, 4/10) clinically did not demonstrate lacrimal drainage changes and were patent on irrigation. The conjunctiva showed focal loss of goblet cells in several areas. Significant changes were noted in the canalicular, lacrimal sac, and the nasolacrimal duct tissues in the form of epithelial hyperplasia, subepithelial inflammation, edema, dilated and congested vessels, and fibrosis. The lacrimal gland, eyelid tissue (excluding tarsal conjunctiva), and cornea showed no significant histopathological changes.

CONCLUSIONS

Clinical and histopathological changes were noted in the lacrimal drainage system of rabbits subjected to topical 5-FU application. These findings can have potential clinical implications for patients receiving 5-FU therapy.

Developing the rabbit canalicular injury model: Biophysical changes of masterkaR stents and implications for future research

BACKGROUND

To describe the preparation of a rabbit lacrimal canalicular injury model, assess the canalicular healing, and determine the suitability of this model to study the biophysical changes of mono-canalicular stents.

METHODS

Twelve canaliculi of twelve eyes of six healthy New Zealand white rabbits were included in the study. A canalicular injury model was prepared under general anesthesia. The injury was then repaired using modified Masterka^R stents and peri-canalicular wound closure. The stents were extubated at eight weeks, and specific surgical techniques used to obtain the healed canaliculi. Histopathological analysis was carried out on the canaliculi samples, and the stents were examined ultra-structurally using the scanning electron microscopy (SEM).

RESULTS

At eight weeks, the canaliculus maintained its integrity and demonstrated good healing with epithelium continuity. However, the area of incision and suture showed hyperplastic epithelium with significant sub-epithelial fibrosis. Lacrimal irrigation following stent extubation confirmed patency of all the canalicular systems studied. SEM study revealed the biofilm formation and physical deposits over the external, luminal, and adluminal surfaces of all Masterka^R stents with intervening skip areas. Although these changes were seen all over the stent, the most preferential site for physical deposits and biofilm aggregates was the ampullary portion of the stent's head. None of the rabbits showed any evidence of a post-operative ocular infection or local inflammation.

CONCLUSION

Rabbits are good candidates for the preparation of a lacrimal canalicular injury model. The canalicular tissues demonstrate changes following repair. The biophysical changes on the extubated stents resembled those obtained from the humans.

Nasolacrimal stent with shape memory as an advanced alternative to silicone products

Epiphora is the overflow of tears typically caused by obstruction or occlusion of the nasolacrimal duct. More attention is required to address this global health issue owing to the increase in air pollution. Implantation of a silicone stent is the preferred treatment for epiphora; however, introducing a silicone stent into a narrow duct with complex geometry is challenging as it requires guidance by a sharp metal needle. Additionally, silicone can cause adverse reactions such as biofilm formation and tear flow resistance due to its extreme hydrophobicity. To overcome these problems, in this study we developed a new type of biocompatible shape memory polymer (SMP) stent with elasticity capacity for self-expansion. First, SMPs in the form of x%poly(ε-caprolactone)-co-y%poly(glycidyl methacrylate) (x%PCL-y%PGMA) were synthesized via ring opening polymerization by varying the molar ratio of PCL (x%) and PGMA (y%). Second, the shape memory and mechanical properties were tuned by controlling the crosslinking degree and concentration of x%PCL-y%PGMA solution to produce a test type of SMP stent. Lastly, this 94%PCL-06%PGMA stent exhibited more standout critical functions in a series of in vitro and in vivo experiments such as a cell growth-supporting level of biocompatibility with nasal epithelial cells without significant inflammatory responses, better resistance to biofilm formation, and more efficient capacity to drain tear than the silicone control. Overall, 94%PCL-06%PGMA can be suggested as a superior alternative to the currently used materials for nasolacrimal stents. STATEMENT OF SIGNIFICANCE: Silicone intubation (stenting) has been widely used to treat nasolacrimal duct obstruction, however, it can cause adverse clinical effects such as bacterial infection; presents procedural challenges because of the curved nasolacrimal duct structure; and shows poor drainage efficiency stemming from the highly hydrophobic nature of silicone. In this work, we describe an innovative shape memory polymer (SMP) as a superior alternative to conventional silicone-based materials for nasolacrimal duct intubation. We demonstrate the clear advantages of the SMP over conventional silicone, including a much higher drainage capacity and superior resistance to bacterial infection.

Intervention using a novel biodegradable hollow stent containing polylactic acid-polyprolactone-polyethylene glycol complexes against lacrimal duct obstruction disease

Lacrimal duct obstruction disease (LDOD) is a common ophthalmologic disease. Stent implantation surgery is one of the most effective therapies. In this study, we intended to find out the satisfactory biodegradable stents containing poly-L-lactic acid-polycaprolactone-polyethylene glycol (PLLA- PCL- PEG) complexes for therapeutic application in LDOD. Stents made of PLLA- PCL- PEG complexes in various ratios, were prepared and used in vitro to determine stents with appropriate mechanical properties and shorter range of bio-degradation for study in vivo. Thirty-two rabbits were randomized into eight groups of four eyes each in advance for test in vivo. The selected stents were implanted into the left lacrimal ducts of 16 rabbits and silica gel stents as the control for the other 16 rabbits. At four points in time (1, 4, 10 and 16 weeks after the implantation), weight loss rate (WLR) of the stents was measured and analysed. To access the change of lacrimal duct, fluorescein excretion test, lacrimal duct endoscopy and histopathological testing were conducted. The stent containing PLLA: PCL6: 4+ 15%PEG was selected for study in vivo. Analysis of weight loss rate (WLR), fluorescein excretion test, lacrimal duct endoscopy and histopathological testing indicated that the selected stent was biodegradable and caused minimal stimulation and earlier tissue restoration in the lacrimal epithelium compared with the silica gel stent used as the control. The study results suggest that the PLLA: PCL6: 4+ 15% PEG stent is a satisfactory biodegradable stent as a promising alternative for therapeutic application in LDOD, which showed tissue compatibility, biodegradation and adequate mechanical intensity.

[Developing the optimal protocol for balloon dacryoplasty]

AIM

To develop the optimal protocol for balloon dacryoplasty (DCP) through an experiment.

MATERIAL AND METHODS

The experiment enrolled 12 Chinchilla rabbits (24 eyes). DCP protocol for group 1 (5 rabbits, 10 eyes) implied two dilations of 90 and 60 sec followed by another two of the same duration, while in group 2 (5 rabbits, 10 eyes) all four dilations were of 90 sec. The balloon was moved proximally before the every third dilation. The remaining 2 rabbits (4 eyes) who did not receive balloon DCP constituted the control group. The animals were killed on days 1, 3, 7, and 14. In all cases nasolacrimal duct morphology was studied.

RESULTS

By day 14 after the procedure, inflammatory changes in nasolacrimal ducts either had resolved (protocol 1) or persisted (protocol 2).

Treating epiphora in adults with the Wilhelm plastic nasolacrimal stent: mid-term results of a prospective study

The objective of the present study was to evaluate, in a prospective, single-center study, the effectiveness of the Wilhelm-type stent used in interventional radiology for the management of epiphora. Patients (n = 104; mean age 64 [range 25–88]; 33 male and 71 female) with severe epiphora had the stents inserted (135 stents in 115 eyes) to treat obstruction of the nasolacrimal system. The etiology of the obstruction was idiopathic in 83 cases, chronic dacryocystitis in 31, cases and postsurgical status in 1 case. The overall technical success rate of stent placement was near 94%. Resolution of epiphora was complete in 105 cases and partial in 3 cases. During a mean 13-month follow-up (range 1 week to 28 months), the median duration of primary patency was 11 months, and the percentage of patency at 6 months was 60.8%, at 1 year was 39.6%, and at 2 years was 25%. Stents malfunctioned in 54 cases, and all were easily withdrawn except in 1 case. Of these 27 cases, patency recovered spontaneously in 9 and by way of a second stent in 18. Secondary patency was 50%. Factors presdisposing to lower primary patency are inflammatory etiology and location of the obstruction. The benefit of stent deployment is clear with respect to the resolution of epiphora in candidate patients for percutaneous treatment. Technical and/or design improvements would be welcomed.

Identifying an appropriate animal model for the nasolacrimal drainage system

PURPOSE

To determine a suitable animal model for further characterization of the nasolacrimal drainage system.

METHODS

A comprehensive Pubmed literature search was performed to locate articles pertaining to the histology or anatomy of the nasolacrimal drainage system in research animals. The histology of 2 nasolacrimal drainage systems of a cynomolgus monkey was also evaluated using hematoxylin-eosin stain.

RESULTS

Sixteen articles were identified that describe the anatomy and/or histology of the nasolacrimal drainage system in rabbits, rats, pigs, sheep, goats, horses, deer, llamas, camels, apes, dogs, and cats, with significant homology between these models. Notable exceptions were found in rat histology and rabbit anatomy. In the few experiments using animal models to investigate the nasolacrimal drainage system, the rabbit model was the most commonly used system. Light microscopy of the cynomolgus monkey nasolacrimal drainage system revealed markedly similar anatomy and histology to that of humans.

CONCLUSIONS

Literature review demonstrates a great deal of similarity in the anatomy and histology of the nasolacrimal drainage systems of 12 mammalian species. Although a common ophthalmic research animal, the rat model has significant histologic differences that prevent its use for comparison with the human lacrimal excretory system. Current literature suggests that despite anatomical variation, the rabbit animal model could potentially be used for further characterization of the nasolacrimal drainage system because it pertains to clinical applications in human patients. Preliminary light microscopy suggests that the cynomolgus monkey may be a superior model for nasolacrimal drainage research, but further studies are required.

Randomized comparison of nasolacrimal cryoplasty versus plastic lacrimal stenting in the management of epiphora in adults

PURPOSE

To evaluate the efficacy of plastic polyurethane stents compared with nasolacrimal cryoplasty in the management of epiphora in adults.

MATERIALS AND METHODS

Patients (N = 37; mean age, 64 years; range, 34-86 y; six men, 31 women) with severe epiphora with partial/complete obstruction of the nasolacrimal system were randomized to have a plastic stent inserted (n = 19) or to undergo balloon dilation cryoplasty (n = 18). Both procedures were conducted on an outpatient basis. Patency was assessed with Kaplan-Meier curves.

RESULTS

Initial technical success rate and immediate resolution of epiphora was complete in all cases. At 6 months of follow-up, outcomes were already significantly different between the treatment groups and hence the study was discontinued. Plastic stent placement achieved a primary patency rate of 59.6% at 6 months, compared with 12.4% in the cryoplasty group (P < .0004). Multivariate analysis indicated that other measured variables (sex, age, etiology, previous treatment, and the interventional radiologist's expertise) had no significant effect on the outcomes (P > .05).

CONCLUSIONS

Initial success was good in both treatment groups, with nasolacrimal plastic stent placement achieving a level of primary patency superior to the cryoplasty procedure for the relief of epiphora on short-term follow-up. However, long-term outcome evaluation is needed before stent placement can be recommended as an alternative to more established surgical procedures.