2.2.5. Sensimed Triggerfish® Contact Lens (Sensimed; Lausanne, Switzerland)

This soft contact lens, approved by the United States Food and Drug Administration (FDA), has a sensor that takes automated recordings for 24 h of the corneoscleral junction's dimensional changes, which are thought to correlate with changes in IOP. The lens is composed of silicone and has a high oxygen transmissibility to prevent hypoxia of the cornea. The sensor transmits data wirelessly to a circular antenna taped to the periorbital region. The antenna then sends the data via a cable to a recorder that the user wears hanging from the neck. The contact lens has been shown to be safe and well-tolerated, with a fair amount of reproducibility in diurnal IOP patterns [34]. A clinical trial [35] of 33 patients compared the slope of IOP increase from wake to sleep position measured by the contact lens sensor in one eye versus that of which was measured by the pneumatonometer in the contralateral eye; there was a high correlation coefficient of 0.914, suggesting that the contact lens sensor is accurate in detecting IOP changes.

A unique advantage of using a contact lens is it allows for the generation of a diurnal curve, even when the user is sleeping. This device can detect IOP elevations outside of clinic hours that may provide clues as to why a patient's glaucoma is progressing despite normal IOPs measured in clinic. In fact, a multicenter study that included 445 patients showed that certain variables measured by the contact lens, such as the night bursts ocular pulse frequency standard deviation and night bursts ocular pulse amplitude standard deviation correlated with prior rates of visual field progression [36].

#### 2.2.6. Other Contact Lenses in Development

Researchers in South Korea developed a soft contact lens that measures IOP using a strain sensor [37]. The contact lens was tested on rabbit and human eyes, and it demonstrated reliable and accurate IOP measurements. Different from Triggerfish®, this contact lens sends data wirelessly to a smartphone; thus, allowing for the real-time monitoring of IOP and eliminating the need to carry a bulky recording device.
