Medical Applications of Contact Lenses

Contact lenses have been a popular option for correcting refractive error for many years, and manufacturers continue advancing the technology to produce new lenses that benefit our patients. We’ve seen developments in soft lens technology such as higher oxygen transmissibility through silicone hydrogel materials, reduced complication and infection rates with daily disposable lenses, improved toric lens stability, and parameter availability for high refractive errors.

This article focuses on the growing medical uses of contact lenses, including disease monitoring, drug delivery, optical enhancements, and more (Table).¹

DISEASE MONITORING

Systemic Disease

The tear film was previously thought to be a biomarker only for ocular disease detection, but its immune properties can also assist in diagnosing various systemic conditions. For example, Alzheimer disease presents with increased levels of dermcidin, lacritin, lipocalin-1, and lysozyme-C in the patient’s tear film.

Diabetes

The tear film of a patient with diabetes will have elevated glucose, advanced glycation end proteins, and cytokine changes. Blood glucose is typically monitored by the finger-prick method, a procedure that uses a lancet to acquire a blood sample. Two potential noninvasive means of glucose monitoring using contact lenses are being researched: the optical detection method² and the electrochemical method.³ Optical detection relies on glucose binding to sensors, resulting in fluorescent change and interpretation by a photodetector or smartphone. The electrochemical method relies on more complex components and chemical reactions to produce an electrical current proportional to glucose within the tear film. The electrochemical method is more accurate, although more cumbersome compared with the optical detection method. The main drawback in glucose monitoring via tear film is the 20-minute lag between changes in blood glucose levels and changes in tear glucose levels. This time period can be critical for patients who experience a severe hypo- or hyperglycemic crisis.

Cancer

Cancer detection by tear film biomarkers is another area of research in the contact lens space. A tear film protein called lacryglobin is elevated in patients with lung, breast, colon, and prostate cancer, and in those with a family history of cancer. Contact lenses may be useful in acquiring direct measurement with biosensors or indirect measurement of accumulation of tear properties on the lens and after removal.

Ocular Disease

Glaucoma

IOP readings, specifically dynamic measurements that account for circadian changes and short-term fluctuations, are critical in the management of patients with glaucoma, especially those with end-stage or progressive disease. In-office IOP readings are limited because they provide only a static IOP reading (ie, at one point in time). Contact lens technology can provide accurate readings over a length of time. An IOP change of 1 mm Hg produces a 3 mm change in corneal curvature in an average-sized cornea, and devices have been developed to detect such changes.

The Sensimed Triggerfish (Sensimed) continuous ocular monitoring system is FDA approved for the 24-hour measurement of IOP.⁴ It uses an 11.5 mm–wide circular gauge that corresponds to the corneo-scleral junction and location of highest deformation due to IOP changes. The device provides 288 IOP data points throughout a 24-hour period, is available in three base curves, and has an oxygen transmissibility of 119 Dk/t. The most common side effects are transient blur, conjunctival hyperemia, and punctate keratitis, which have been reported to resolve within 24 to 48 hours.³

One limitation of this lens is potential discomfort due to its thickness (two to three times that of a traditional soft lens, and/or its stiff modulus). Another limitation is the indirect IOP measurement by corneal curvature compared with in-office applanation tonometry measurements, potentially making it difficult for the clinician to compare and determine next steps for clinical management.

Dry Eye Disease

Contact lenses may also aid in the diagnosis of dry eye disease by measuring tear film osmolarity, inflammatory cytokines, and blink rate. It is well known that blink rate is reduced during near activities, such as computer use and reading.⁵ A contact lens with a biosensor may be useful for monitoring both rate and completeness of an individual’s blink.¹

Contact lenses are also being evaluated for the treatment of dry eye disease with dehydration-resistant materials and lacrimal gland stimulation.¹ Prevention of ocular surface dryness with dehydration-resistant materials using electro-osmotic flow can be achieved via an ionic contact lens material with arcuate anodes and cathodes to the lens surface, which promotes an upward tear flow within the contact lens. The electrical current is supplied by a biocompatible battery or wireless induction.

In addition, a patent for a stimulator chip on a contact lens surface was recently filed with the goal of stimulating tear production and, therefore, goblet cell secretion by electric stimuli.¹ No clinical studies have been released on the safety or efficacy of the device at this time.

Color Blindness

The use of color filters in contact lenses has been helpful for patients with color vision deficiency. The X-Chrom contact lens (ReVision Optometry) is a red contact lens placed on one eye to darken yellow-green objects and make orange objects look more red. ChromaGen contact lenses (Chromagen) are soft lenses with seven hues and light, medium, and dark densities.

DRUG DELIVERY

There is a great deal of promise in the use of contact lenses for ocular drug delivery. Contact lenses have the potential to overcome limitations related to patient adherence and bioavailability with traditional eye drop methods. However, there is still much to be discovered with contact lens delivery for individual drugs because specific drug and contact lens material combinations must allow for appropriate uptake and release in order for the medication to be effective. The medication used with a specific contact lens material and shape must be able to sustain the full amount of treatment time.

Medications currently being studied for delivery by contact lens include lubricant-releasing drugs, cyclosporine, corticosteroids, glaucoma drugs, and anti-allergy medications.¹ Notably, Acuvue Theravision with Ketotifen (Johnson & Johnson Vision Care) was recently approved by the FDA for the prevention of ocular itch due to allergic conjunctivitis. It also corrects myopia and hyperopia in patients with less than 1.00 D of astigmatism.⁶ Ketotifen is reported to provide fast-acting and long-lasting relief for up to 12 hours.

Myopia Management

In 2019, MiSight 1 day contact lenses (CooperVision) were FDA approved for use in slowing myopia progression in children.⁷ One limitation of the MiSight lens is the need for astigmatic correction, which is not available in a toric design. Orthokeratology is another known method of reducing myopia by contact lens.

OPTICAL ENHANCEMENTS

Contact lens technology is continuously aiming to provide enhanced optics. Specifically, new techniques and data are being studied to reduce higher-order aberrations, especially for those with keratoconus and/or corneal irregularity.¹ Accommodating contact lenses for presbyopia are also being studied by both mechanical and electric methods.¹ The mechanical method relies on the eyelids to apply pressure to the contact lens to change its shape and dioptric power while a person performs near work, such as reading.

MORE TO COME

This review of contact lenses used beyond the correction of refractive error is a good starting point for getting familiar with their many applications but is only a partial insight into the future of contact lens practice. There are many exciting developments in the contact lens pipeline to keep an eye out for and potentially integrate in your practice.