Written by Jamie Saito ‘25
Edited by Surya Khatri '24
45 million people in the United States rely on contact lenses to correct their vision [1]. Unfortunately, about 50% of contact lens wearers experience dry eye symptoms, which leads to decreased wear time or the use of rewetting drops [2]. The eye produces a tear film to cover its surface. This 3 to 10 microliter volume layer protects, lubricates, and smooths the surface of the eye [3]. However, wearing contact lens interferes with the normal tear film, splitting it into two layers. Because these layers are thinner, the tear film eventually evaporates, causing discomfort, itching, dryness, and irritation [2]. For this reason, scientists have focused on preventing Contact Lense Induced Dry Eye (CLIDE) but altering the design of a normal contact lens.
Scientists at the Terasaki Institute for Biomedical Innovation have developed a contact lens that may tackle this issue. This prototype includes microchannels within the lens, which prevents the tear film from being split into two layers [4]. Further, to ensure that the tears do not remain stagnant, these contacts are designed to optimize flow between the two layers. To achieve this, scientists studied how eyelid pressure and motion during a blink affects the contact lens and optimized their design so that the tear film will cycle between the microchannels [4].
For the lens itself, researchers used a poly(HEMA) hydrogel, which is a commonly used material for soft contact lenses. Poly(HEMA) is thus a biocompatible polymer that would cause adverse effects to the eye. To develop this prototype, the researchers sought to optimize how they would fabricate the lens itself. Since contact lenses are thin and the microchannels needed to be precise, they had to experiment with the fabrication process of their poly(HEMA) contact lenses.
Researchers started with a 3-D printed resin mold but found that this required too much time and repetition to create precise microchannels. They therefore used a silicone polymer mixture, which could easily be removed when the hydrogel was set while maintaining the integrity of the microchannels [4]. This created smooth, consistent, and high-quality microchannels that could be as thin as 30 μm, 30 times smaller than previous poly(HEMA) hydrogels [2]. To test the integrity of these microchannels, the researchers immersed the hydrogels in a dye solution for 10 hours, the average wear time for contact lenses [2]. They found no leakage of dye and verified the stability of microchannels under an optical microscope. These findings suggest that the fabrication method of these lenses create effective microchannels to promote the adequate tear flow.
To study the flow rate of these poly(HEMA) contact lenses, the researchers designed a system that could mimic the pressure and motion of an eyelid. They used a fluorescent solution to visualize the flow of tears. In their simulation condition, the ideal prototype lens had microchannels with square cross sections arranged in an circular, arc-like shape [2]. This design retained the functionality of contact lens while also maintaining optical transparency and biocompatibility [2]. The tears were able to flow from the outer layer of the tear film on the lens surface to the bottom layer beneath the contact lens [4]. This exchange in liquid should prevent CLIDE because the layers are not stagnant and thus will not evaporate.
While this prototype is a promising step toward a new age of contact lenses, researchers hope that they can explore other polymer materials to make the contact lens. While Poly(HEMA) is biocompatible, it has low oxygen permeability, which may cause hypoxia in the eye [5]. Future iterations of these designs may include polymer materials with a higher oxygen permeability. These researchers may also manipulate the water content of the hydrogel to see how this affects the properties of the contact lens, such as oxygen permeability and refractive index [5]. By incorporating a microfluidic channel into the contact lens, researchers have created a simple and effective solution to alleviate the discomfort and irritation associated with CLIDE. This technology may significantly impact the lives of contact lens wearers worldwide.
References
1. CDC. Contact Lens Fast Facts [Internet]. Centers for Disease Control and Prevention. 2021 [cited 2023 Apr 10]. Available from: https://www.cdc.gov/contactlenses/fast-facts.html
2. Zhu Y, Nasiri R, Davoodi E, Zhang S, Saha S, Linn M, et al. A Microfluidic Contact Lens to Address Contact Lens-Induced Dry Eye. Small. 2023;19(11):2207017.
3. Chang AY, Purt B. Biochemistry, Tear Film. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Apr 10]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK572136/
4. Contact lenses to treat dry eye syndrome [Internet]. ScienceDaily. [cited 2023 Apr 10]. Available from: https://www.sciencedaily.com/releases/2023/01/230130112431.htm
5. Gispets J, Solá R, Varón C. The influence of water content of hydrogel contact lenses when fitting patients with ‘tear film deficiency.’ Contact Lens Anterior Eye. 2000 Jan 1;23(1):16–21.
6. Fonn D. Targeting Contact Lens Induced Dryness and Discomfort: What Properties Will Make Lenses More Comfortable. Optom Vis Sci. 2007 Apr;84(4):279.
7. Image Citation: https://www.warbyparker.com/learn/can-you-shower-with-contacts