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J.J. Ma, C. Bellevile, M. Nouri, E. Ahmed, C.H. Dohlman; Interferometry for a Non-contact, in vivo Method to Measure Intraocular Pressure using Silicone MEMS (Micro-electro-mechanical Systems) Photolithography Based Chips on a Keratoprosthesis (Kpro) . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4703.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Glaucoma is the most significant long-term complication of keratoprosthesis patients. There presently exists no method to measure IOP other than tactile sensation. The purpose of this project is to develop a reliable method of measuring intraocular pressure using a Fabry-Perot interferometer. Methods: Different MEMs were evaluated; those feasible were tested. In vitro experiments were performed to validate their precision, accuracy and proof of principle. Two types of pre-calibrated MEMs were placed on the Kpro using two different adhesives. The altered Kpro (KproTr) was tested in vitro in enucleated pig eyes while pressure was controlled by intraocular cannulation (IOC). A KproTr was then implanted into a previously studied New Zealand albino rabbit model. Results: Qualitative assessment for biocompatibility of the KproTr compared the Kpro revealed no significant differences when degree of inflammation (cells/fibrin), erythema, neovascularization, absence of corneal melt, dellen formation, discharge, or intact red reflex were evaluated up to 14 weeks post-op. A vascular retroprosthetic membrane was associated with the Kpro (at 4 weeks). This was not present on the KproTr. Cavity length measurements through air and Kpro as well as in the in vitro pig-eye model were reproducible with standard deviations (SD) that varied depending on the MEMS probe used. In vivo, the ability to accurately measure pressure using a fibre optic MEMS probe in a Kpro rabbit was validated. There was no significant difference between repeat measurements in the range from 0 mmHg to 100mmHg (p values: 0.18, 0.62, 0.68). The correlation coefficient between actual pressure change by IOC and repeat measured cavity lengths were 0.997, 0.998, 0.998. In vivo KproTr cavity length measurements were reproducible with SD's that varied depending on the MEMS probe. At 14 weeks post-op, the KproTr rabbit developed a complication that was thought to be independent of the transducers mounted on the KPro. Conclusions:This is the first time that a physical parameter (IOP) has been measured using a non-contact MEMs interferometry technique. The inert MEMs and their adhesives appear to be at least as well tolerated in the rabbit eye as compared to a regular Kpro. This study demonstrates the feasiblity of an in-vivo non-contact MEMS-based method of IOP measurement. Accuracy and precision should be improved with new technique/instruments; long-term biocompatibility studies will be necessary.
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