Implantation and testing of a novel episcleral pressure transducer: A new approach to telemetric intraocular pressure monitoring
Measurement of intraocular pressure (IOP) is an essential tool in monitoring glaucoma. Single IOP assessments during clinical routine examinations represent punctual values and are not able to identify IOP fluctuations and spikes. Telemetric IOP measurements are able to monitor IOP during the day and night, and are location-independent. Six telemetric episcleral IOP sensors were investigated after minimally invasive subconjunctival implantation in 6 eyes of 6 New-Zealand-White rabbits. Three of the 4 edges of the implant were fixated intrasclerally with non-absorbable sutures. The sutures were stitched into the edges of the implants' silicone rubber encasements. Telemetric IOP measurements were validated 1 week, 4 weeks, 8 weeks, 12 weeks and 30 weeks after implantation. For each validation the anterior chamber was cannulated and connected to a height-adjustable water column. Different intracameral pressure levels (10–45 mmHg) were generated by height adjustment of the water column. Measurement reliability and concordance between telemetric and intracameral IOP was validated using Bland-Altman analysis. Overall comparison (10–45 mmHg) between telemetric and intracameral pressure revealed a standard deviation of ±1.0 mmHg. A comparison of pressure values in the range between 10 and 30 mmHg revealed a standard deviation of ±0.8 mmHg. Device deficiency was related to follow-up length: 4 weeks after implantation, 3 of the 6 sensors showed malfunction, with all sensors having failed 30 weeks after implantation. The most likely reason for the sensor malfunction is the loss of hermeticity as a result of penetration of the encasement during the episcleral fixation, resulting from the lack of preformed suture holes at the implants encasement. However, no clinical signs of injury or inflammation of the conjunctiva, sclera, implantation site or any other involved structures were observed, except for an expected mild short-term irritation postoperatively. The episcleral pressure transducer for telemetric IOP monitoring is able to assess IOP without the need for invasive intraocular surgery. Episcleral implantation is an easy and safe procedure and can be undone very easily, so even temporary implantation and IOP measurements could be possible in the future. Sensor malfunction over time is a problem that needs to be addressed. Improvements in sensor encapsulation and especially preformed suture holes could significantly decrease the failure rate and increase durability.