Continuous Monitoring of Intraocular Pressure from the Sclera

Glaucoma is an optic neuropathy often associated with increased intraocular pressure (IOP) that can lead to impaired vision and blindness. Frequently asymptomatic, this eye disease may be undetectable until vision is severely compromised. The primary goal of glaucoma management is to prevent progressive nerve damage by maintaining a reduced IOP in order to preserve vision and maintain a patient’s quality of life. IOP is a major risk factor for glaucoma, however, studies have shown that throughout a 24-hour period IOP is not constant and fluctuates throughout the day. This results in the clinical dilemma that diurnal changes in IOP, particularly during sleep, in patients with glaucoma may not be accurately evaluated during the regular practitioners’ office hours when diagnosis and management are provided. Since lowering and stabilizing IOP remains the only proven way to reduce disease progression, the development of a continuous IOP monitoring device, for human use, is critical. To date, there remains no commercially available non-invasive human device that can reliably and accurately measure IOP throughout the 24-hour period. There is an experimental contact lens device available in Europe, but there are significant disadvantages using a silicon contact lens on the cornea. The objective of this thesis was to demonstrate the efficacy of a noninvasive strain gauge sensor, placed on the sclera, to detect changes in IOP. The specific aims are to provide proof-of-principle for a novel, scleral mounted device for measuring IOP by: (1) establishing whether IOP can be recorded from the conjunctival and scleral surface using enucleated porcine eyes; (2) establishing whether IOP can be recorded from the conjunctival surface in a live pig model; and (3) to examine the inflammatory response of a hydrogel contact lens placed overnight on the scleral, bulbar conjunctiva as a plausible carrier for the strain gauge sensor. Changes in IOP can be accurately assessed by measuring changes in the radius of curvature of the sclera in enucleated tissue as well as in a live porcine model. Analysis of silicone hydrogel contact lenses, approved for overnight wear on the cornea, showed that they may be safely mounted on the upper bulbar conjunctiva and present a promising carrier material for a 24-hour IOP monitoring device. These proof-of-principle experiments are an essential step to the realization of a safe, scleral mounted, 24-hour IOP recording device that has the potential to significantly impact the way glaucoma is diagnosed and managed.Ph