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| Proof-of-Concept for Optical Intraocular Pressure Sensor to Detect Glaucoma |
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Glaucoma is an optic nerve disorder caused by raised intraocular pressure. Among many drugs and agents causing glaucoma, tobacco has been found to be one of the important agents. [1-3] Glaucoma is the second leading treatable cause of blindness in the United States, and one of the top three causes of blindness worldwide. An estimated 66.8 million people worldwide were projected to suffer from it in the year 2000, with 6.7 million suffering from bilateral blindness. In developed countries, less than 50% of those with glaucoma are aware of their disease. This rate is even lower in the developing world.[4] In the United States, an estimated 1.6 million people ages 40 years or older have primary open angle glaucoma (POAG). However, an estimated one-half of the glaucoma in the United States goes undiagnosed.[5] Furthermore it is estimated that up to 50% of axons can be lost before any visual field defect is apparent.[6] A sensitive and widely available method of screening for glaucoma can help to identify glaucoma patients at an earlier stage of the disease. Since standard glaucoma therapy is associated with a decrease in the incidence of visual field loss,[7] earlier diagnosis and therapy may significantly reduce blindness due to this disease.
It is known that the IOP within the same eye of a person undergoes drastic changes (oscillations) during the 24 hours in a day (Fig. 1 left), thus a pressure measurement at a doctor's office can at best only get a snapshot in time of the currently prevailing intraocular pressure, missing all the other oscillations. Consequently a sporadic IOP measurement may still not prevent glaucomatous damage from happening.
A self-checking non-contact IOP monitoring system with daily readout that measures the true intraocular pressure is very important and much needed. Beyond the screening for high IOP there are issues related to drug therapy for glaucoma and how to titrate and monitor these treatments. While on therapeutic eye drops one often sees salient and transient periods of breakthrough elevation of the IOP which can damage the eye. Therefore the proposed optical intraocular pressure sensor (OIPS) will red flag even one such violation. This close monitoring of the IOP would greatly help the control and optimization of glaucoma drug therapy, especially for patients that already have the diagnosis of glaucoma.
The primary focus of this project is the fabrication of a proof-of-concept unpowered optical pressure sensor. The greatest technology risk associated with an “implantable” monitoring system is the mechanism for powering the detector and the readout system. Therefore, our envisioned sensor will be composed of a flexible reflective thin-film grating which will change grating pitch (and therefore reflected wavelength) with ambient pressure variation. The currently envisioned intraocular pressure sensor device is an extremely small optical thin-film sensor encapsulated within a flexible hermitic shell: it is extremely small (<1mm3), requires no power source, and is sensitive (+/-2mmHg). |
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| Figure 1: The pressure sensor concept. A) An H-PDLC reflection grating with no applied pressure. The reflection wavelength is slightly above 500nm. B) An H-PDLC grating with applied pressure. The reflection wavelength has been changed to below 500nm. The small arrows are the applied pressure. |
References:
[1] “Hydrostatic Pressure Response of Polymer-dispersed Liquid Crystal Gratings”, M. Ermold, K. Rai, A. K. Fontecchio, J. Appl. Phys., 97, 104905, 2005. |
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