Contact lenses of the future

Systemic disease detection

Contact lenses can assist in detecting biomarkers in the tear film that may indicate systemic disease. For example, patients with Alzheimer disease can have increased levels of dermcidin and lacritin, whereas patients with thyroid eye disease may have increased levels of IL-6, IL-17, and IL-7. Cancer biomarkers can also be detected in tear samples, specifically with increased levels of lacryglobin, a tear film protein of patients with colon, lung, breast, and prostate cancer as well as patients with a family history of cancer. A particular area of interest has also been glucose monitoring for patients with diabetes, as the contact lenses provide a noninvasive method of detecting blood sugar levels, whereas invasive finger-prick testing is currently considered the gold standard.¹

Ocular disease detection/management

Of particular interest to eye care providers, contact lens sensors can be used to monitor IOP. A commercially available, FDA-approved silicone soft contact lens device that permits extended monitoring of IOP is available and known as the Triggerfish contact lens sensor (Sensimed). Although the device does not directly measure IOP, it is able to sense dimensional changes in corneal shape, which correspond to changes in ocular biomechanics properties and volume as well as IOP.¹ The device is meant to stay on the ocular surface for 24 hours and contains 2 strain gauges, a microprocessor, and an antenna.² The strain gauge transfers information to an adhesive antenna that is attached to the orbit of the patient. The antenna then transfers information to a portable recorder worn by the patient. Findings from clinical studies have demonstrated successful tolerability in both patients with glaucoma and those without. Findings from a number of clinical studies investigating the Triggerfish contact lens have shown the most frequent complications to be transient blurred vision, conjunctival hyperemia, and superficial punctate keratitis.²

An additional application of contact lenses to monitor ocular conditions lies in the field of dry eye syndrome (DES). A prototype contact lens has been designed to evaluate tear osmolarity, tear evaporation rate, and ocular surface temperature. Cytokine/chemokine detection in the tear film is also being studied, which would allow point-of-care diagnostics in aiding the diagnosis and management of DES. Contact lenses can also be used as a portable reader to detect lysozyme levels, which are traditionally low in patients with Sjogren syndrome, a known culprit in DES. A contact lens blink-monitoring system has also been described. Although conceptual in nature, this system relies on transient reductions in light falling on an integrated photosensor, which would allow monitoring of the completeness and frequency of eyelid blinking.¹ Ocular surface temperature has also been studied in relation to DES, as an unstable tear film can cause increased tear film evaporation and therefore cooling of the ocular surface. This can be studied with an optical temperature sensor, whereas temperature-sensitive liquid crystals exhibited a color change. In cases where lacrimal gland stimulation is needed to produce more tears, there is a patent for an electronic stimulator in a contact lens, which delivers intranasal electrical stimulation to stimulate tearing and promote goblet cell secretion.¹

A major implication of contact lenses lies in diabetic retinopathy, the most common cause of blindness in the working population. Oxygen consumption of the rod photoreceptors is greatest during dark adaptation, potentially causing hypoxia in the diabetic retina and driving further disease progression. Researchers have proposed various methods to deliver light to the retina during eye closure to minimize hypoxia during sleep. A silicone elastomer contact lens has been developed that incorporates 24 radioluminescent gaseous tritium light sources arranged in a radial pattern, with a clear central 3-mm aperture. Another application of contact lenses is in patients with color vision deficiency, where management has been mostly limited to using color filters, such as the X-Chrom lens. A large-scale plasmonic surface was developed and embedded on a rigid contact lens to address deuteranomaly, the most common class of color vision deficiency.¹

Antimicrobial contact lenses

Although contact lenses for refractive purposes provide many therapeutic and cosmetic benefits for patients, they have been linked to multiple contact lens–related diseases, many due to pathogens on the ocular surface. Contact lens usage can lead to favorable conditions for microorganisms to multiply, due to compromise of the epithelium from lens-cornea contact as well as corneal hypoxia. Manufacturing microbicidal contact lenses and contact lens cases against various pathogens, such as viruses, bacteria, and fungi, has been known to occur by 4 processes: 1) direct penetration of microbial cells, 2) modification of microbial-substrate interfaces, 3) interference with the quorum-sensing mechanism of microbial cells, and 4) generation of reactive oxygen species. Silver is known for its antimicrobial potential against a broad spectrum of microorganisms, including gram-negative bacteria, gram-positive bacteria, fungi, and protozoa. Since 2004, silver-impregnated polymers have been used to synthesize commercial antimicrobial lens cases. This releases silver ion concentrations of 10 μg/L into the case for 1 month. Additionally, the contact lens itself can be bound with silver nanoparticles that show promise in antibiofilm and antimicrobial potential. Organoselenium has also been applied to antimicrobial contact lens cases and has the added benefit of being less harmful to the corneal-epithelial cells.³

Drug delivery contact lenses

Ophthalmic drug delivery systems are usually inadequate, with eye drops allowing approximately 95% of the active substance to be lost by tear drainage. Contact lenses can release the medication onto both sides of the ocular surface, limiting the drug loss and extending time on the ocular surface. Drugs released from soft contact lenses can stay on the ocular surface for at least 30 minutes, approximately 15 times longer compared with regular eye drops. Prolonged contact time of the drug with the cornea can increase its bioavailability up to 50% compared with 1% to 5% of eye drops. Soft contact lenses, in particular, are the material of choice for this purpose compared with rigid contact lenses due to their hydrophilic properties, biocompatibility, and comfort of use. Soaking soft contact lenses in a drug solution is the simplest method of applying them to the ocular surface.⁴ Incorporating vitamin E into the contact lenses can significantly increase drug release duration from a few hours to several days.⁵

References

1. Jones L, Hui A, Phan CM, et al. CLEAR - contact lens technologies of the future. Cont Lens Anterior Eye. 2021;44(2):398-430. doi:10.1016/j.clae.2021.02.007

2. Dunbar GE, Shen BY, Aref AA. The Sensimed Triggerfish contact lens sensor: efficacy, safety, and patient perspectives. Clin Ophthalmol. 2017;11:875-882. doi:10.2147/OPTH.S109708

3. Khan SA, Lee CS. Recent progress and strategies to develop antimicrobial contact lenses and lens cases for different types of microbial keratitis. Acta Biomater. 2020;113:101-118. doi:10.1016/j.actbio.2020.06.039

4. Rykowska I, Nowak I, Nowak R. Soft contact lenses as drug delivery systems: a review. Molecules. 2021;26(18):5577. doi:10.3390/molecules26185577

5. Peng CC, Burke MT, Carbia BE, Plummer C, Chauhan A. Extended drug delivery by contact lenses for glaucoma therapy. J Control Release. 2012;162(1):152-158. doi:10.1016/j.jconrel.2012.06.017