We've been working on developing a sophisticated eye model for almost 4 years now. Fortunately, we've had a ton of help from many researchers and engineers along the way. We would like to give a special thank you to the Centre for Ocular Research and Education for supporting us from the very start. This blog post will highlight some of the cool research we did using our first generation eye model, the OcuFlow!
We first wanted to developed an eye model to test drug delivery with contact lenses. At the time (in 2014), we were still using vials to test the release of drugs from contact lenses. Vials are cheap and convenient, and they can be found in almost every lab. The only problem is that they don't resemble the human eye at all. So after a few months of simple engineering, we came up with the OcuFlow (photograph below); a simple model that mimics the tear flow and tear volume of the front of the eye, as well as the mechanical rubbing and air exposure that's produced during a blink.
Typically, whenever we tested drug delivery with contact lenses in a vial, we would observe a burst release of the drug from the lens, followed by a period of non-release. This should not surprising since if you immerse a lens in a large volume of solution, you would expect that everything on the lens to unload immediately. Interestingly, when we used the OcuFlow, the drug release from the lenses started showing variations between different materials. On some lens materials, the release was gradual and slow, while on other lens types, the drug release was much faster (Reference 1-3).
At the time, we were also interested in the delivery of antifungal drugs from contact lenses. Fungal eye infections are extremely difficult to treat, and patients have to be treated with eye drops at hourly intervals for almost a month. That's a lot of eye drops! The idea was that if we could make a contact lens that could deliver fungal drugs over the course of week, it would make the treatment process a lot more bearable and increase patience's compliance. To this end, we developed novel contact lens materials that delivered antifungal drugs, but we needed a way to test if these materials would deliver enough drugs to kill the fungi.
We then thought of using the OcuFlow eyeball as a potential test model. We made the eyeballs out of agar, a substance that allows microorganisms such as fungi that cause eye infections to grow, and started growing fungi that normally infect the eye. We then placed our contact lenses infused with antifungal drugs on the infected eyeballs to see if it would kill the fungi. We found that certain antifungal drugs were more effective than others, and that certain contact lens-drug combinations did effectively kill the fungi. Interestingly though, we found certain lens types actually caused the fungi to adapt and change to a more virulent type... ugh that's bad (Reference 4)! We'll definitely have to revisit this topic in the future.
Our model worked very well for drug delivery with contact lenses, so we wanted to see if we could use it for other studies involving contact lenses. We then turned our attention to contact lens deposition, a highly debated topic that is linked to contact lens discomfort. Contact lens discomfort is a big problem for the industry, because it's one of the primary reasons that people stop wearing lenses. There is a theory that the deposition of tear film components, such as lipids and proteins, are associated with contact lens discomfort.
We used the OcuFlow to study both protein and lipid deposition with lenses collect in the lab. Traditionally, these studies would have been done using a vial, where the lenses would be submerged in a large volume of artificial tear fluid. In our studies, we found that there were significantly less proteins and lipids deposited on the contact lenses using the OcuFlow model than a vial (Reference 5,6), suggesting a more biologically representative model.
If you are interested in learning how to make the OcuFlow, check out our video paper publication (Reference 7). Feel free to use it in your research, but please do credit us when you publish.
References
1. Bajgrowicz M, Phan CM, Subbaraman LN, Jones L. Release of ciprofloxacin and moxifloxacin from daily disposable contact lenses using an in vitro eye model. Investigative ophthalmology and visual science. 2015; 56 (4): 2234-42
2. Phan CM, Bajgrowicz M, Gao H, Subbaraman LN, Jones L. Uptake and release of fluconazole from daily disposable contact lenses using a novel in vitro eye model. Optometry and Vision Science. 2015; 93(4): 387-94.
3. Phan CM, Bajgrowicz-Cieslak M, Subbaraman LN, Jones L. Release of moxifloxacin from contact lenses using an in vitro eye model: Impact of artificial tear fluid composition and mechanical rubbing. Translational Vision Science & Technology. 2016; 5 (6):3.
4. Phan CM, Bajgrowicz M, Subbaraman LN, Jones L. Effects of antifungal soaked silicone hydrogel contact lenses on Candida albicans in an agar eye model. Eye & contact lens. 2015; 42(5): 313-7.
5. Walther H, Phan CM, Subbaraman LN, Jones L. Differential deposition of fluorescently tagged cholesterol on commercial contact lenses using a novel in vitro eye model. Translational Vision Science & Technology. 2018; 7 (2): 18.
6. Qiao H, Phan CM, Walther H, Subbaraman LN, Jones L. Depth profile assessment of the early phase of lysozyme on soft contact lens materials using a novel in vitro eye model. Eye & Contact Lens. 2017; (4) 2: 11-18
7. Phan CM, Walther H, Gao H, Rossy J, Subbaraman LN, Jones L. Development of an in vitro platform to test contact lenses. Journal of Visualized Experiments. 2016; (110): e53907.