The Interfacial Dewetting and Drainage Optical Platform (i-DDrOP) machine recently developed at Stanford is promising to make contact lenses more comfortable. The i-DDrOP, which enables scientists to closely study the eye’s protective tear film, was described in a report published in the March issue of Investigative Ophthalmology and Visual Science.
Researchers at the Fuller Lab in the Stanford Department of Chemical Engineering developed i-DDrOP to examine the properties of the meibum layer, a thin layer of lipid overlying the tear film. The scientists found that the viscoelastic properties of the meibum layer maintain the structure of the tear film and may also play a role in preventing the tear film from evaporating.
The study was co-authored by Saad Bhamla Ph.D. ’15, MIT undergraduate Chew Chai, chemical engineering Ph.D. candidate Noelle Rabiah, postdoctoral researcher John Frostad and Professor of Chemical Engineering Gerald Fuller.
According to Bhamla, who conducted the work as a graduate student, pressing a contact lens on top of the meibum layer can cause the tear film to dissipate in a process known as dewetting, which leads to painful symptoms such as dry eye.
“Imagine the eyelids rubbing against a dry surface versus a lubricated surface,” Bhamla said, referring to the problematic nature of previous lenses.
Due to water’s strong surface tension, the aqueous tear film would rapidly withdraw to form more compact surfaces if left alone. The meibum layer keeps the surface of your eye protected by forming a monolayer that maintains the integrity of the tear film.
i-DDrOP simulates both the tear film and meibum layer, allowing contact lens manufacturers to test prototype lenses on an artificial system before beginning clinical trials. Bhamla anticipates that lens testing using a device instead of a patient will eliminate a major bottleneck in contact lens innovation.
“Clinical trials take tens of years,” Bhamla said. “[Contact lens manufacturers] don’t ship out new contact lenses every month because of this.”
Contact lenses today are evaluated for metrics such as strength, oxygen permeability and contact angle, but not wetting capability. According to Fuller, who is the principal investigator, the project originated in response to industry concerns.
“This company was producing solutions for [dry eye] and asked us to look at a particular component of the tear film to see if there was anything in it mechanically that was important for tear film stability,” Fuller said.
i-DDrOP parameters have substantial flexibility when it comes to testing contact lenses. Previous artificial systems were bogged down by constraints, including only being operable at room temperature. According to Fuller, testing can now be done at different temperatures and humidities, which more realistically matches the experience of contact lens wearers.
i-DDrOP is now being used by multiple contact lens manufacturers for research, perhaps heralding rapid advances in contact lens comfort in the near future.
“How can you not study such a problem?” Bhamla said. “It’s right in front of your eyes.”
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