Characterization and design of soft contact lens sensor

Abstract

Glaucoma is a leading cause of blindness in the world. The primary clinical indicator for glaucoma is intraocular pressure (IOP). Patients identified as having high IOP in screening are subjected to further tests and possible treatment if confirmed. Existing screening practices involve measurement of the IOP in the clinic during office hours. Measurement during office hours is known to have inherent inaccuracies because it would miss the IOP peak that occurs typically at night. More accurate measurements can be done with an overnight stay in the hospital, but the cost is a major concern. IOP during the day and at night can be measured using contact lens sensor worn by a patient. A new thin contact lens sensor with high sensitivity is developed to continuously measure the IOP. Successful sensing of the IOP depends on optimization of the embedded electrical elements within and the contact lens materials and geometry. In this study, the effects of contact lens and sensing coil geometry on the sensing behavior of the contact lens sensor were examined; and the correlations between contact lens sensor signal and curvature were investigated as a function of the fitting. Tight, standard and loose fitting conditions were tested. The results showed tight fitted lenses have better IOP tracking (better sensor linearity) and reproducibility. The curvature of contact lens sensor was found to have minimal effect on the sensitivity, but thickness is shown to be an important parameter for good sensing. Correlation factors for the thin contact lens sensors can be 3X larger than the sensitivity of the thick sensors. Circuit coil diameter and number of turns are shown to increase the sensitivity by up to 95% and 39%, respectively when larger diameter and more coil turns were used. Based on the experimental results, an optimized design of contact lens sensor is developed. IOP monitoring with contact lens sensor was shown on ex vivo porcine eye and in vivo rabbit eye. Preliminary human trial was also done.

Date of Award	2014
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology