Glaucoma microsensors

Injectable devices that can monitor IOP and adjust therapy 24/7 are on the horizon

Howard Larkin

Posted: Monday, July 22, 2019

Marlene Moster MD

Microelectronics now in development may soon solve one of the biggest problems in managing glaucoma – detecting and responding to fluctuations in intraocular pressure (IOP).

An IOP microsensor small enough for a mouse eye already exists, and a prototype 3mm x 6mm implantable device combining an IOP sensor with a drug reservoir designed to respond to IOP spikes is not far off, Marlene Moster MD told the Glaucoma Subspecialty Day at the 2018 American Academy of Ophthalmology Annual Meeting in Chicago.

Further miniaturisation and integration will greatly improve the usability, reliability and affordability of such devices over existing 24-hour IOP monitoring devices, making them practical for widespread clinical use, she added.

“Eventually, a series of ultra-miniature tools that communicate with each other will have the potential to transform not only our monitoring of pressure, but will enable more effective treatment of glaucoma in real time. In several years the sensors will be delivered through a needle at the slit lamp in your office,” said Dr Moster, of Wills Eye Hospital, Philadelphia, USA.

The value of continuously measuring IOP is well established, Dr Moster said. Studies going back more than 15 years show that IOP is generally higher at night than day, and when lying down rather than sitting (Liu, Zhang, Kripke, Weinreb. Invest Ophthalmol Vis Sci 2003; 44:1586-1590).

More recently, contact lens sensor studies found patients with normal tension glaucoma have a wider range of IOP fluctuation than non-glaucoma patients (Tojo N et al. J Glaucoma 2017; 26(3): 195–200); that sleep position affects IOP and may contribute to progression (Beltran-Argullo et al. Br J Ophthalmol 2017;101(10):1323-1328); and that larger IOP fluctuations may help identify patients at higher risk of visual field loss (De Moraes CG et al. JAMA Ophthalmol 2018; 136(7):779-785).

However, while promising, current continuous IOP sensors have significant drawbacks, Dr Moster noted. Contact lens-based sensors are expensive – about €500 per single-use disposable lens plus €6,000 for a handheld reader/charger – and cumbersome, requiring an antenna mask to download data. Long-term accuracy issues also have emerged in tests.

Implantable monitors address the accuracy issue and eliminate expensive consumables, making them much easier to use, Dr Moster said. The current model of the Eyemate-IO (Implandata Ophthalmic Products, Hanover, Germany), which received the CE mark in 2017, has been implanted in the ciliary sulcus through a 3.2mm incision in 44 patients to date, with a planned reduction to 2.5mm in a future version.

According to unpublished data, the current Eyemate-IO design has produced no instances of sterile inflammation, or angle narrowing, pigment dispersion or pupillary distortion seen in a trial of a bulkier early version tested in six patients in the ARGOS-01 study (Koutsonos A et al. Invest Ophthalmol Vis Sci 2015; 56(2):1063-9). The device has documented differences in the range of IOP fluctuation using different medications, which may help customise therapy. Versions in preclinical tests will allow standalone insertion into the suprachoroidal space or vitreous body.

Similarly, the QSmart IOP pressure system (Qura Inc), in preclinical development, is incorporated into a posterior chamber IOL for insertion in dog eyes and may be attached to a capsular tension ring for humans. It communicates directly with devices or tablets and can issue real-time warnings of IOP spikes through wireless networks.

A device measuring less than 1.0 cubic mm has been tested in mouse eyes (Ha D, et al. Biomed Microdevices 2012;14:207–215. Bhamra H, et al. IEEE Trans Biomed Circuits Syst. 2017 Dec;11(6):1204-1215). Combining microsensors with micro-delivery devices could create system capable of detecting and immediately responding to IOP spikes, Dr Moster said. A 1mm x 2mm device with a 100-micron micropump is the wave of the future.

Other developments that will make implanted sensors practical include eliminating handheld devices to recharge and read data, and improved battery life, which currently could reach 20 years. “The future is now,” Dr Moster concluded.