New Insights Into Human Tears Could Lead to More Comfortable Contact Lenses

Stanford Researchers – Developing a Device – Improved Contact Lens

Contact lenses which tend to work well and does not seem to cause any kind of irritation after a day’s long work at the computer, gives the wearer much comfort as though they are not there on their eyes. After several hours of wear, the lenses together with the eyes seem to dry out which could cause some discomfort to the user, thereby outweighing the ease of contact lenses. Stanford researchers have been making attempts to relieve the pain by enhancing the understanding of how natural tears seem to keep our eyes comfortable and by developing a machine to design improved contact lenses.

The work had been motivated in parts by a graduate student’s dry eyes. Saad Bhamla, s Stanford postdoctoral scholar in bioengineering who had conducted the work as a graduate student in chemical engineering laboratory of Gerald Fuller, at Stanford had commented that `as a student, he had discontinued wearing lenses owing to increased discomfort. Focussing on PhD thesis to understand this issue was personal as well as a professional goal’. He is not alone but there are over 30 million Americans presently wearing contact, though around half of them have switched back to glasses due to contact lens-induced symptoms like dry eye.

Tear Film – Process Known as Dewetting

Bhamla together with Fuller doubted that most of the discomfort was the cause of break-up of the tear film, a wet coating on the surface of the eye at the time of a process known as dewetting. They observed that the lipid layer, which is an oily coating on the surface of the tear film, tends to protect the eye’s surface in two important ways, through strength and liquid retention.

By imitating the lipid layer in contact construction, millions of individuals could evade from ocular discomfort. Bhamla and his co-authors in their recent study, summarize two function of the lipid layer wherein one is to provide mechanical strength to the tear film. Lipids in this layer tend to have viscoelastic properties which enable them to stretch as well as support the watery layer below them.

Bhamla compares this protective lipid layer to that of a swimming pool cover where one cannot run on the open water though even a thin cover could offer mechanical strength in supporting the weight of the person. The lipid layer also tends to avertthe tear film from evaporating away. Eyes tend to be around 95 degrees Fahrenheit which is generally warmer than the ambient air and like any liquid on a hot surface; the eye is continually heating its liquid coating thereby losing moisture to the air.

Interfacial Dewetting& Drainage Optical Platform

Fuller had stated that they recognized early-on that the fluid mechanical responses of the lipid layer were just as important as the conventional view which its role was to control the evaporative loss. Moreover it had been gratifying to realize that the combined role of these two forces was now accepted.

The importance of developing comfortable contact lenses, involves the designing of lenses which do not tend to destabilize the tear film. Manufacturers are aware of the importance of protecting the natural tear film of the eye on a contact lens surface to reduce painful symptoms like dry eye, though it is not an easy thing to measure. To resolve this issue, Bhamla and Fuller had developed a device which resembles the surface of the eye which is known as the Interfacial Dewettingand Drainage Optical Platform or i-DDrOP.

It reproduces a tear film on the surface of a contact lens and has enabled scientist and manufacturers to systematically manage the unique array of variables which tend to affect the tear film, inclusive of temperature, various substances, humidity and the way gravity tends to act together with curved surface.