BackgroundGlaucoma is the second leading cause of blindness in the world and the first leading cause of irreversible vision loss. Currently, the primary methodology of testing for the intraocular pressure (IOP) is during clinical office hours, which only provide a limited amount of information on the trends and fluctuations of the IOP. Therefore, a continuous monitoring system is required to properly determine the peaks of pressure and to negate any false results obtained by sparse, clinic hour testing. The objective of this study is to determine the ability of a newly designed contact lens with an embedded microchannel, to accurately measure the fluctuations in the IOP.MethodsExperimentation was completed on fresh enucleated porcine eyes. The contact lens was placed on the porcine eye and utilising a camera the fluid movement, within the microchannel in the contact lens, was recorded. A micro-pressure catheter, threaded into the centre of the vitreous chamber, recorded the true IOP and was compared with the displacement of the indicator fluid within the microchannel.ResultsThe contact lenses showed a consistent linear responsiveness to changes in IOP and robust to the effects of anatomical differences among eyes. The indicator fluid had an average fluid movement of 28 um/mm Hg between all the trials. Additionally, the devices showed the ability to measure both increases and decreases in IOP during cyclical fluctuations.ConclusionThe described inexpensive and non-invasive sensor is able to reliably monitor the IOP changes based on porcine eye model.

Glaucoma is a chronic eye disease where an increase in intraocular pressure (IOP) permanently damaging the optic nerve leading to irreversible vision loss. Intraocular pressure is the main factor for monitoring the progression of glaucoma and has been found to fluctuate throughout the day. A continuous monitoring system can track the fluctuations in the intraocular pressure throughout the day, improving the management of the disease. A novel non‐invasive wearable sensor was created to monitor the fluctuating corneal curvature of the eye and directly relate the deformation to the intraocular pressure. The wearable sensor was able to capture on average 40.8 µm/mmHg with a standard deviation of 29.4 in fluid location per increase in intraocular pressure with an ability to return over 80% back to its original position indicating a good ability to accurately track the fluctuations in the IOP.

A novel, inexpensive, and easy-to-use strain sensor using polydimethylsiloxane (PDMS)  was developed. The sensor consists of a microchannel that is partially filled with a coloured liquid and embedded in a piece of PDMS. A finite element model was developed to optimize the geometry of the microchannel to achieve higher sensitivity. The highest gauge factor that was measured experimentally was 41. The gauge factor was affected by the microchannel’s square cross-sectional area, the number of basic units in the microchannel, and the inlet and outlet configuration. As a case study, the developed strain sensors were used to measure the rotation angle of the wrist and finger joints.

The development of flexible electronic devices has primarily been focused on the production of flat 2-dimensional sensors and has lacked the ability to manufacture devices with complicated 3-dimensional geometry. A mold-based method for manufacturing devices with 3-dimensional geometry that is cost-effective and repeatable is presented herein. This technique is demonstrated by the fabrication of a novel pressure sensor using a 3-dimensional PDMS membrane patterned with a resistive silver nanowire network. The specific geometry of the sensor was chosen to provide a uniform strain distribution along the silver nanowire network. The sensor has a linear response to pressure, a gauge factor of 4–29, and behaves well under repeated cyclical testing. A flat sensor with a 2-dimensional membrane was also manufactured for comparison to the 3-dimensional sensor. It was observed that the flat membrane has a higher gauge factor but has a non-linear response to pressure.

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