IOP Monitoring Contact Lens

About

BACKGROUND Glaucoma is a heterogenous group of eye diseases caused by increases in intraocular pressure (IOP) that damage the optic nerve. It is the second leading cause of blindness globally and the leading cause of irreversible blindness1. It is estimated that the number of people with glaucoma worldwide was 76 million in 2020 and this number is expected to increase to 111.8 million in 20402. The effects of glaucoma are gradual and progress undetected. Vision loss from glaucoma is irreversible so early detection and continuous monitoring are essential to slow the progression of disease. Goldmannn applanation tonometry (GAT) is the gold standard for monitoring IOP levels. The challenge with this technique is that it requires local anesthetic, it must be performed by a trained professional and only a few readings are obtained annually. The IOP is known to fluctuate throughout the day and is impacted by several factors including changes in heart rate and body position. Additionally, the shape of the eye changes with changing IOP and this can be exploited to develop novel IOP monitoring tools. There is increasing demand for an at home continuous monitoring IOP system. Continuous monitoring devices that accurately detect IOP fluctuations, can detect glaucoma, track its progression and allow a more individualized therapeutic response. TECHNOLOGY OVERVIEW A polydimethylsiloxane (PDMS) soft contact lens was developed with an embedded micro fluidic channel. The properties and channel design of the PDSM allow the device to capture changes in the internal volume of the channel, which correspond to changes in corneal curvature. The microchannel is partially filled with an incompressible fluid. Any changes in volume displace the fluid in the microchannel providing a visual indication of changes in corneal curvature. The contact lens will be worn throughout the day and will be used with a cell phone camera to take images of the contact lens periodically. Information can be read at any time of day in either an upright or reclined position. A cell phone app will be used to process the image comparing the location of the fluid with a reference frame built into the contact lens, to measure the IOP reading quickly and accurately. The contact lens-based monitoring device was evaluated to test the accuracy of the contact lenses to capture changes in IOP. Fresh enucleated porcine eyes were selected due to their similar shape and properties to the human eye. Water was inserted into the sclera of the eye using a syringe pump to manually increase IOP between 10 and 34 mm Hg. The IOP was monitored with a Miller Micro-Tio Pressure Catheter Transducer threaded into the other side of the sclera. To evaluate the reliability of the contact lens-based monitoring device three separate contact lens devices were tested twice on a single eye. At baseline and with every 2mm Hg increase in IOP, a picture of the contact lens was taken. The displacement of indicator fluid was calculated by comparing the reference markers included as part of the contact lens device. The indicator fluid showed a linear relationship between fluid displacement and IOP for all devices. The average fluid displacement was 28.5 µm/mm Hg with a SD of 2.4. To assess the ability of the contact lens device to measure the IOP of different eyes, a single device was tested on three eyes. The three eyes had different corneal shape, thickness and biomechanical properties. The indicator fluid was analyzed at baseline and at every 2mm Hg increase in IOP. The movement of indicator fluid showed a linear relationship with increasing IOP for all eyes, at the slopes of 26.4, 29.3 and 28 µm/mm Hg for the eyes 1, 2 and 3. The response was similar between the three eyes with an average fluid movement of 27.9 µm/mm Hg with a SD of 1.5. To track fluctuations in the IOP throughout the day, when the IOP increases the indicator fluid must travel in an anterograde direction and with decreases in IOP the fluid must travel in a retrograde direction. To study this, IOP was cycled between 10 and 40 mm Hg for a total of four cycles and the indicator fluid monitored. There was an initial decrease in indicator travel distance after the first cycle, but in subsequent cycles the indicator fluid returned to 92% of