Implantable Optofluidic Sensor for Assessment of Intraocular Pressure Christina Antonopoulos MD, Mostafa Ghannad-Rezaie, Nikos Chronis PhD, Shahzad Mian MD W.K. Kellogg Eye Center and Department of Mechanical Engineering University of Michigan, Ann Arbor, Michigan The authors of this poster have received research funding from the National Institutes of Health (Grant 1R21NS ). The authors hold no proprietary interest in the material presented herein.

Abstract Purpose: To develop an implantable opto-fluidic IOP sensor that enables long-term continuous monitoring of intraocular pressure. Methods: The design consists of an implantable MicroElectroMechanical Systems (MEMS) pressure sensor that converts IOP variations into spectral signals in the near infrared (NIR) region (700 nm-900 nm). The sensor integrates a pressure-tunable elastomeric microlens with a Quantum Dot (QD) bilayer, each layer having a distinct emission wavelength. A collimated NIR laser beam, focused through the microlens into the QD bi-layer, induces fluorescent excitation of the bilayer. Results: IOP variations can cause changes in the focal length of the microlens which result in changes in the ratiometric fluorescent intensity emitted by the bilayer. Intraocular implantation may occur with: (1) iris fixation, (2) integration into intraocular lenses, (3) integration into keratoprosthesis devices. Conclusion: An implantable, opto-fluidic sensor can enables long-term, continuous IOP monitoring, and is small in size when compared to the other pressure transducers. This device will be used for ex vivo and in vivo testing to establish safety and efficacy.

Purpose To develop an implantable opto-fluidic intraocular pressure sensor that enables long-term, continuous monitoring of intraocular pressure To successfully implant the device into the optic of an intraocular lens, keratoprosthesis or iris-sutured for stand-alone monitoring for use in clinical scenarios in which frequent IOP monitoring is critical (advanced glaucoma) or otherwise unfeasible (keratoprosthetic eyes)

Methods: Sensor mechanism consists of a sealed system of two fluid chambers covered by thin elastomeric membranes; one acts as a deflectable membrane and the other as a microlens coupled with a tunable Quantum Dot (QD) bilayer. When external pressure (intraocular pressure, IOP) is applied the deflectable membrane deflects downwards and by virtue of fluid displacement induces a convex deflection of QD bilayer. The microlens focal length remains constant. A collimated near infrared (NIR) laser beam, focused through the microlens onto the QD bilayer induces fluorescent excitation of the bilayer; the lower layer emits light at wavelength λ = 705nm; the upper layer emits wavelength λ = 800 nm IOP variations cause QD bilayer position to change in the focal plane, bringing the upper layer out of focus and the lower layer in focus and therefore changes in the ratiometric fluorescent intensity emitted by the bilayer. The signals are send back to the external unit for self-read-out

Methods

Results Figure 1: Intraocular pressure versus deflection of deflectable membrane (square, silicone nitride, 297nm thickness) or differing sizes. The external pressure is increased from 1mmHg to 45mmHg. The experiment is repeated for six membranes of each size, all with identical fabrication. The deflection at maximum external pressure ±4.5% and ±3% for the largest and smallest membranes, respectively.

Results Figure 2: The intensity and ratio of light emitted by the Quantum Dot channels as a function of intraocular pressure. The lens focuses on the 800nm QD monolayer at atmospheric pressure. As external pressure is increased, the membrane deflects and moves the 705 nm layer and 800nm layer into and out of the focal plane, respectively. Therefore, the ratio of the signal intensities of the 705nm QD layer and the 800nm QD layer increases. We repeated the experiment for six identically fabricated devices. There is up to ±6% variation in the ratio of channel across devices. The ratio change is statistically significant for 6mmHg change.

Results Figure 3: Long-term response of three identical devices submersed for three weeks in water. Each device response is recorded every 3 days to 20mmHg (A) and 40mmHg (B). A variation in the ratio of ±5% and ±6% is observed for 20mmHg and 40mmHg external pressure, respectively. (A)(B)

Discussion We are developing an implantable, opto-fluidic sensor that (i) enables long-term, continuous IOP monitoring, (ii) is small in size, and (iii) is theoretically safely implantable into the eye Safe implantation in the eye will theoretically generated a data set of continuous IOP measurements to enhance the management of any form of glaucoma Our device is applicable to patients with glaucoma, ocular hypertension, glaucoma suspects, patients in whom prior anterior segment surgery precludes measurement or monitoring of IOP (e.g. keratoprosthetic eyes)

Conclusions An implantable, opto-fluidic sensor can potentially enable valuable, long-term, continuous IOP monitoring for clinicians Future goals include in vivo testing to establish safety and efficacy and implantation into intraocular lenses and keratoprostheses