Comparative in vitro flow study of 3 different Ex-PRESS miniature glaucoma device models

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Fluid Dynamics

Background:

• Glaucoma is a leading cause of irreversible blindness.
• The Ex-PRESS miniature glaucoma device is used to manage intraocular pressure.
• Understanding device flow characteristics is crucial for optimizing glaucoma treatment.

Purpose of the Study:

• To evaluate the flow characteristics of three Ex-PRESS glaucoma device models (P-50, R-50, P-200).
• To determine the impact of pressure on flow rate and resistance for each model.
• To compare the performance of different Ex-PRESS models in a controlled laboratory setting.

Main Methods:

• A gravity-driven flow test was employed.
• Three samples of each Ex-PRESS model underwent testing at five pressure levels (5-25 mm Hg).
• Flow rate (Q) and resistance (R) were measured and calculated.

Main Results:

• Flow rate was significantly dependent on pressure.
• The P-200 model exhibited higher flow rates and lower resistance than P-50 and R-50 models (P<0.0001).
• P-50 and R-50 models showed similar flow rates despite differing tube lengths.

Conclusions:

• Ex-PRESS mini shunts function as flow resistors with consistent resistance.
• Internal tube diameter is the primary determinant of flow and resistance.
• All tested models demonstrated flow rates exceeding that of a healthy human eye's outflow facility.