Korean J Ophthalmol.  2016 Jun;30(3):225-233. 10.3341/kjo.2016.30.3.225.

Performance of and Pressure Elevation Formed by Small-diameter Microtubes Used in Constant-flow Sets

• Sohn SW
• Noh MD
• Lee JH
• Kim KN
• Kim CS
• Ahn BH

• KMID: 2373978
• DOI: http://doi.org/10.3341/kjo.2016.30.3.225

Abstract

PURPOSE
We explored the performance of and pressure elevation caused by small-diameter microtubes used to reduce overfiltration.
METHODS
Using a syringe pump-driven constant-flow setting (2 µL/min), pressures were measured for polytetrafluoroethylene (PTFE) microtubes 5 mm in length with inner diameters of 51, 64, and 76 µm and for polyether block amide (PEBAX) microtubes with an inner diameter of 76 µm. Experiments (using microtubes only) were initially performed in air, water, and enucleated pig eyes and were repeated under the same conditions using intraluminal 9/0 nylon stents.
RESULTS
The pressures measured in air in 51-, 64-, and 76-µm-diameter PTFE microtubes differed significantly (22.1, 16.9, and 12.2 mmHg, respectively; p < 0.001), and that of the 76-µm-diameter PEBAX microtube was 15.8 mmHg (p < 0.001 compared to the 12.2 mmHg of the 76-µm-diameter PTFE microtube). The pressures measured in water also differed significantly among the three microtubes at 3.9, 3.0, and 1.4 mmHg, respectively, while that in the PEBAX microtube was 2.6 mmHg (all p < 0.001). Using the intraluminal stent, the pressure in water of the three different PTFE microtubes increased to 22.6, 18.0, and 4.1 mmHg, respectively, and that in the PEBAX microtube increased to 10.5 mmHg (all p < 0.001). Similar trends were evident when measurements were performed in pig eyes.
CONCLUSIONS
Although microtubes of smaller diameter experienced higher pressure in air, reduction of the inner diameter to 51 µm did not adequately increase the pressure attained in water or pig eyes. Insertion of an intraluminal stent effectively elevated the latter pressures. PEBAX microtubes created higher pressures than did PTFE microtubes.

Keyword

Intraluminal stent; Intraocular pressure; Microtube; Polyether block amide; Polytetrafluoroethylene

MeSH Terms

Animals
Disease Models, Animal
Glaucoma/physiopathology/*surgery
*Glaucoma Drainage Implants
Intraocular Pressure/*physiology
Ophthalmologic Surgical Procedures/*instrumentation
*Polytetrafluoroethylene
Prosthesis Design
Swine
Polytetrafluoroethylene

Figure

• 

  Fig. 1 Light micrographs of the cut ends, and average internal diameters of the microtubes and 9/0 nylon thread. (A) 51-µm polytetrafluoroethylene (PTFE) tube. (B) 64-µm PTFE tube. (C) 76-µm PTFE tube. (D) 76-µm polyether block amide tube. (E) 9/0 nylon. (F) Tube with a 20-mm length of intraluminal 9/0 nylon; one end of the thread was inserted into the tube 6 mm from the distal end.

• 

  Fig. 2 Experimental setup for fluid flow in air. The setup consisted of a perfusion pump with a syringe, pressure transducer, pressure detector, silicone chamber, and microtube.

• 

  Fig. 3 Experimental setup for fluid flow in water. All settings were identical to those in Fig. 2, except that the tip of the microtube was connected to a tube filled with distilled water.

• 

  Fig. 4 Experimental setup for fluid flow in an enucleated pig's eye. All settings are identical to those in Fig. 2, except the tip of the microtube was positioned on the sclera beneath the conjunctiva and Tenon's capsule.

• 

  Fig. 5 Cumulative pressure profiles for microtubes of different diameters and materials. (A) Microtubes without a stent in air. (B) Microtubes with an intraluminal 9/0 nylon stent in air. (C) Microtubes without a stent, connected to a water chamber. (D) Microtubes with an intraluminal 9/0 nylon stent, connected to a water chamber. (E) Microtubes without a stent, connected to a pig eye. (F) Microtubes with an intraluminal 9/0 nylon stent, connected to a pig eye. PTFE = polytetrafluoroethylene; PEBAX = polyether block amide.

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