Glaucoma drainage devices – a microfluidic analysis

The experiment detailed in this short review article is originally based on a research paper titled “Construction of a novel microfluidic experimental setup for testing recent glaucoma drainage devices”. The research paper was authored by Emre Kara, Ahmet İhsan Kutlar, and Kıvanç Güngör and published in the journal ‘Current Directions in Biomedical Engineering’. The study explores testing of latest glaucoma drainage devices through a new microfluidic experimental setup, and in the process, identify areas of improvement in their design.

Abstract

Glaucoma is an eye disorder which affects the optic nerve, damaging it over the course of several years due to a prolonged elevation of intraocular pressure (IOP). It is also the second most common cause of blindness, according to the World Health Organization. From their report about this disease, glaucoma is not only considered a serious ocular disease affecting individuals, but has established itself as a health problem for communities. Mostly owing to technological advancements in recent years, implants have proved to be very useful in treating glaucoma. In spite of the continued effort towards design and development of glaucoma drainage devices (GDD), there are quite a few unsolved issues with the technology. Most currently used GDDs are structurally very simple and pose multiple challenges such as reversed flow, choking and a course interval of pressure control. It is the need of the hour to conduct experiments and explore the flow behaviour within these intricate devices. Through this research study, a precise microfluidic flow control setup is assembled to analyze and specify the in-vitro performance of actively employed GDDs. The preferred setup for this study includes – a pressurized fluid reservoir, ELVEFLOW flow control device, microfluidics flow sensors, pressure sensors and a data analysis system.

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Introduction

In simple terms, glaucoma is one of the ophthalmic diseases caused by pressure within the eye above permitted limits. Obstruction within the passageways of this flowing fluid – aqueous humour (AH) that fills the front and back chambers of the eye is seen as the primary cause of this disease. This disease completely disables the ability to see completely or sometimes partially. In reference to a WHO report from 2010, it was estimated that the 8.4 million individuals who had become blind from glaucoma would increase to 11.1 million cases by 2020. In addition to primary glaucoma, 60.5 open-angle and close-angle glaucoma cases would reach close to 79.6 million cases by 2020. [1]

Owing to extensive research, glaucoma treatment can be approached in three ways: 

• Medical therapy
• Surgical treatment
• Glaucoma drainage devices (GDDs)

Glaucoma drainage devices (GDDs) are considered as the most reliable treatment for glaucoma in the last 20 years due to various design improvements. Research is still ongoing, trying to come up with the ideal GDD, and the Ahmed Glaucoma Valve (AGV) can be considered the closest device to ideal. [2]  Despite it being widely accepted, the AGV acts as a flow blocker after implantation [3], and needs to be switched on and off at specific pressures like a real valve. Experimental studies to address these issues with GDD design should be conducted, which is exactly what this study is aimed towards.

Aim and objectives

The primary factors to be studied while testing a GDD are as follows: 

• Whether the device can continue to function as expected after a certain period of time
• Testing the effectiveness of the device to postoperative complications such as hypotony, and diplopia
• A range of reversed flow, flow blockage and pressure control situations.

Experimental setup

In this experimental setup, the list of components mentioned below is used: 

• Pressurized fluid reservoirs
• Elveflow OB1 MK3+ (Microfluidic Flow control instrument)
• Pressure sensors
• Flow sensors
• Visual analysis by USB microscope
• Silicone pipes and insulated box
• Data analysis unit
• Compressor

The experimental setup is shown in the image below in Figure 1. In Figure 2, the list of components along with their working specifications for the experiment are mentioned in a tabular form.

Calibration of the pressure control unit

In this experimental setup, the calibration is performed in 2 stages – First, on initial connection of the pressure control unit to the computer, the pressure input is set to a desired 2 bar maximum output. Second, if the pressure output exceeds the limit, the pressure regulator is calibrated. Further details regarding the calibration can be found in the Elveflow User Guide. [4]

After completion of the calibration procedure, a pressurized air versus flow rate graph is plotted to categorize needed pressure for the needed flow rate of the saline solution.

Key findings

The main aim of this study is to analyse and identify the in-vitro performance of actively employed glaucoma drainage devices on the glaucoma treatment by assembling a precise microfluidic setup that can rigorously test these GDD’s for various real-time situations.

In this study, with the assembly of an accurate microfluidics setup, the analysis of in-vitro performance of glaucoma drainage devices include: 

• A more accurate and faster response system than the syringe pump
• Testing different GDD designs with the same setup to perform a comparative analysis
• Commenting about possible design improvements
• Proposing a GDD design that takes into account ergonomic sensitivities during implantation.

These promising results were achieved by the researchers with the help of a highly accurate pressure driven flow control equipment in Elveflow OB1. It gives much reliable results that can be replicated by other researchers, and used to make design improvements to widely used glaucoma drainage devices. To gather further insight into this study, please refer to the original research paper by Emre Kara et al..

If you’re interested in what the authors have achieved, and would like to know more about these precise flow control devices, feel free to contact our team of experts.

Acknowledgement

This work is supported by the Scientific and Technological Research Council of Turkey-
TUBİTAK 3001 Project (Grant No: 117M971).

References