title: Comparative in vitro flow study of 3 different Ex-PRESS miniature glaucoma device models.
abstract: OBJECTIVE
  To determine the flow characteristics of the 3 different models of the Ex-PRESS miniature glaucoma device in a controlled laboratory study.
  
  
  METHODS
  The 3 different Ex-PRESS models (P-50, R-50, and P-200; Optonol Ltd; now Alcon Lab) were tested using a gravity-driven flow test. Three samples of each of the 3 Ex-PRESS models were subjected to a constant gravitational force of fluid at 5 different pressure levels (5 to 25 mm Hg). Four measurements per sample were taken at each pressure level. The main outcome measure was flow rate (Q) (µL/min). Resistance (R) was calculated by dividing pressure (P) by the measured flow (Q).
  
  
  RESULTS
  The flow rate was primarily pressure dependent. The P-200 model (internal diameter 200 µm) showed a statistically significant higher flow rate and lower resistance compared with both the P-50 and R-50 models (internal diameter 50 µm) (P<0.0001). The P-50 and R-50 models demonstrated similar flow rates (P=0.08) despite their difference in tube length (2.64 vs. 2.94 mm).
  
  
  CONCLUSIONS
  The 3 models of the Ex-PRESS mini shunt behaved in vitro as simple flow resistors by creating a relatively constant resistance to flow. Tube diameter was the only parameter with significant impact on flow and resistance. All models demonstrated flow rates per unit of pressure much higher than the outflow facility of a healthy human eye.
authors.affiliation: Department of Ophthalmology, University of California San Francisco (UCSF), San Francisco, CA 94143-0730, USA.
authors.forename: Stephan
authors.initials: S
authors.lastname: Estermann
authors.forename: Kanokwan
authors.initials: K
authors.lastname: Yuttitham
authors.forename: Julie A
authors.initials: JA
authors.lastname: Chen
authors.forename: On-Tat
authors.initials: OT
authors.lastname: Lee
authors.forename: Robert L
authors.initials: RL
authors.lastname: Stamper
mesh_terms: D000085:Acetates / Q000378:metabolism*; D004338:Drug Combinations; D020327:Glaucoma Drainage Implants; D006112:Gravitation; D066298:In Vitro Techniques; D008903:Minerals / Q000378:metabolism*; D010477:Perfusion; D011312:Pressure; D012965:Sodium Chloride / Q000378:metabolism*
chemical_list: D000085:Acetates; C030660:BSS solution; D004338:Drug Combinations; D008903:Minerals; D012965:Sodium Chloride