Intraocular pressure measurement at the choroid surface: a feasibility study with implications for implantable microsystems

AIMS To demonstrate that a sensor, which is inserted through the sclera and placed in intimate contact with the choroid, can reliably detect changes in the intraocular pressure (IOP). METHODS A manometer was used to control the IOP of three cadaver eyes in steps of 7 mm Hg. A piezoresistive pressure sensor was used to measure the pressure at the choroid through a 2.5 mm diameter hole that was surgically removed from the sclera. Data were collected for two configurations; with the sensor: (i) rigidly attached to a miniature positioning stage, and (ii) sutured to the sclera. RESULTS Both configurations accurately tracked the manometer pressure from 10 mm Hg to 47 mm Hg. For the fixed sensor cases, the average difference between the pressure measured at the choroid and in the anterior chamber was 0.8 mm Hg for the three eyes. For the sutured sensor case, the average difference was 2.1 mm Hg—although a significant portion of this was attributed to an initial offset. The standard deviations at each pressure level for all of the choroid measurements were under 1.0 mm Hg. CONCLUSIONS Small changes in IOP can be accurately measured by a sensor in contact with the surface of the choroid, for both a fixed sensor configuration and for a sensor sutured to the sclera. These results are the first step in the realisation of a surgically implantable microsensor to monitor IOP for patients suffering from low tension and other difficult to manage forms of glaucoma.