It's no secret that contact lenses can be really uncomfortable — ask anyone who's ever worn a pair. Roughly half of contact wearers switch back to glasses in order to protect themselves from irritating side effects, like dry eyes. Researchers are trying to come up with ways to make lenses more-friendly to the human eye, but it isn’t an easy thing to measure. A new device invented by researchers from Stanford University, however, may have the answer.

The device was inspired by one student's personal experience with the condition. "As a student, I had to stop wearing contact lenses due to the increased discomfort," said Saad Bhamla, a Stanford University postdoctoral scholar in bioengineering, in a press release. "Focusing my...thesis to understand this problem was both a personal and professional goal."

Bhamla suspected most of the problems with contact lenses were rooted in the break up of the tear film, a wet coating on the eye. The film is protected by the lipid layer, an oily coating right on the surface. Bhamla said this protective layer is like a swimming pool cover: Since you can’t run on open water, a thin tarp can provide enough strength to support a person’s weight.

If researchers could figure out how to mimic this effect in contact lens, perhaps people could avoid discomfort.

"You will sometimes see the guards at Stanford Avery pool run over the surface of the covered pool," Bhamla said. "The mechanical structure is very thin, but it protects the whole bulk of the liquid. If the swimming pool is shrunk to 1/100th the width of a hair, it is a good representation of the tear film with a lipid layer replacing the tarp."

The lipid layer also protects the tear film from evaporating. Eyes are usually a little warmer than the surrounding air, and like any liquid on a hot surface, the eye is constantly losing moisture.

"We recognized early-on that the fluid mechanical responses of the lipid layer were just as important as the conventional view that its role was to control evaporative loss," explained Gerard Fuller, who runs the chemical engineering lab Bhamla studies in. "It’s been gratifying to realize that the combined role of these two forces is now accepted."

Bhamla said that currently, many researchers are studying contact lenses by holding them up to light and dipping them in water, then checking to see if the tear film breaks up. He felt he could do better.

The scientists decided to build a device that mimics the surface of the eye, called the Interfacial Dewetting and Drainage Optical Platform or i-DDrOP. The machine reproduces the tear film on the surface of a contact lens, and allows scientists and manufacturers to examine all the variables that affect the film: temperature, humidity, different substances, and gravity.

With the ability to measure these factors, manufacturers may be able to develop truly comfortable contact lenses.

Source: Bhamla S, Chai C, Rabiah N, Frostad J, Fuller G. Instability and Breakup of Model Tear Films. Investigation ophthalmology and visual science. 2016.