Sensing Intraocular Pressure in Order to Study Glaucoma

Glaucoma, a disease which causes blindness due to optic nerve degeneration, affects nearly 2.3 million Americans who are over 39 years of age. Although the specific mechanics are not known, high intraocular pressure (IOP) is known to be the single biggest factor that contributes to the death of the optic nerves. Researchers at Purdue University are designing an implantable pressure sensor that would be able to give continuous IOP readings; the current plan is to implant the device into a mouse so that the mechanisms of glaucoma may be more accurately studied. Methods of measuring IOP already exist, but they are not always reliable considering IOP can change dramatically even within a single day. By comparison, a continuously monitoring sensor is much more valuable.

The present design is overall circular in shape (as seen in the included picture). The device would be implanted within the anterior chamber of the mouse’s eye. This specific paper concerns itself with the fabrication of the actual sensing portion of the device.

Two fabrication processes were tested: use of a sacrificial photoresist layer and Membrane transfer via Parylene to Parylene bonding. The former method necessitates creation of the sensor on a silicon carrier wafer. The wafer is subsequently removed and a hole is drilled, which is eventually sealed, in order to remove the sacrificial photoresist layer. It was discovered that this method required creation of a multilayer structure, which would increase the thickness of the device.

In the latter method, the top and bottom parts of the sensor are constructed on two separate copper sheets. The top parts of the sensor are then attached using Parylene to Parylene thermal bonding, and the copper sheets are subsequently removed. This process is able to produce a smaller sensor that is still within the desired sensitivity range.

The sensor produced via the second process was attached to a mold representing the rest of the device. The researchers needed to test whether the sensor would still function properly if the device as a whole were bent, which was a requirement so that the implant would fit inside the mouse’s eye. It was discovered that the needed radius of curvature did not affect the sensor’s sensitivity at all. Overall, the feasibility of producing an adequate micro-sensor for detecting IOP was determined to be true.

I chose to talk about this article because I am interested in how researchers study diseases about which little is known. I also believe this device might be used as a detection method for glaucoma in high-risk individuals.

2011HaIOPSensorPublished.pdf