The concept of using contact lenses (CLs) to assist in the diagnosis of ocular disease goes back over a decade, with the development and commercialization of an “electronic contact lens” to monitor intraocular pressure (IOP) throughout the day (Mansouri and Shaarawy, 2011; Mansouri and Weinreb, 2012; Mansouri et al, 2015). This is helpful to account for circadian variations, which cannot be easily measured overnight, and also acute variations in IOP between supine (during sleep) and upright stance. It is suggested that IOP spikes have a direct impact on glaucomatous progression (Sit, 2009), and thus, continuous monitoring over 24-hour periods through CL sensors can prove helpful in monitoring progression and in altering treatments, if necessary.

This device was the first to contain a variety of components (battery, antenna, and other miniaturized electronics) that permit on-eye sensing and off-boarding of information to a recording device.

Other Applications

While this remains the only commercial electronic CL device to date, there are many other opportunities for which such devices could prove valuable, especially with respect to the tear film. The Tear Film and Ocular Surface Society (TFOS) Dry Eye Workshop II (DEWS II) report has outlined diagnostic criteria for dry eye disease (DED) (Wolffsohn et al, 2017). Because CLs are placed on the ocular surface, they can be utilized to measure some of these diagnostic signs, and prototype CLs have been used to measure tear osmolarity, tear evaporation rate, and ocular surface temperature (Chiou, 2019). These could be utilized in clinical settings to aid the diagnosis and continuous monitoring of DED management.

An alternative approach is to use fluorescent dyes integrated into the CL material. There are prototypes of both scleral (Yetisen et al, 2020) and silicone hydrogel (Badugu et al, 2018) lenses that have embedded sensors and fluorescent dyes, and quantitative measurements of the tear film could be collected with a fluorescence imaging device.

Another novel prototype uses holographic grating sensors embedded into the CL. When the lens is immersed into the tear film, the polymer material within the sensor grows or shrinks, causing a change in color of the hologram. The color changes are related to the concentration of various tear components (Alexeev et al, 2004). Inflammatory cytokines in the tear film are another diagnostic sign of DED (Roy et al, 2017). Currently, there are no CL-integrated cytokine sensors; but, this concept is feasible, as a study has reported on the activity of a tear film protein (lysozyme) after its collection by a CL worn for 15 minutes (Ballard et al, 2020).

Made You Blink

Blink frequency and completeness are also important factors in the diagnosis and management of DED. Blink sensors could be integrated into the CL material to monitor this continuously throughout the day (Pugh et al, 2015). It is also possible to use colored CLs with sensors; the degree of dehydration and pressure changes on the lens can alter its color (Wang et al, 2020). For example, changes in ocular surface temperature, such as cooling when the tear film evaporates, will cause the color within the material to change.

It could also be possible to monitor the body’s vascular system through the blood vessels of the retina and conjunctiva. One patent describes annular rings in the CL that send ultrasonic pulses toward the retina and reflect off of it (Pugh, 2018). The reflected pulse provides vascular pulsation data and imaging of the retinal blood vessels. This technology could help patients monitor their general vascular health and notify them if there are emergent changes.

Another patent uses an optical sensor within the CL to measure the pulse rate and blood oxygen levels through the conjunctiva as an indicator of general vascular health (Ho and Amirparviz, 2015). This technology can also be used to monitor other anterior segment ocular disease associated with hyperemia, such as allergic conjunctivitis, DED, uveitis, etc. CLS

For references, please visit www.clspectrum.com/references and click on document #316.