Nanotech Makes Your Brown Eyes Blue

ACS MEETING NEWS

Beauty is in the eye of the beholder, they say, but what if the beholder wants more beautiful eyes? Colored contact lenses have been steadily gaining popularity among those who want to add a little more pizzazz to their peepers. And these days, colored contacts arent just for making eyes more dazzling. Vision care companies are making colored contacts that give athletes an edge and improve the appearance of disfigured eyes.

Chemists from Ciba Vision and Bausch & Lomb told attendees of the American Chemical Societys recent national meeting in Washington, D.C., about the chemistry behind their companies colored contact lenses. The talks were part of the Cosmetic Nanotechnology: Polymers and Colloids in Personal Care symposium, sponsored by the Division of Polymer Chemistry and cosponsored by the Society of Cosmetic Chemists, the Division of Colloid & Surface Chemistry, and the Women Chemists Committee.

Walt Bassett, global head of R&D for fashion wear at Ciba Vision, in Duluth, Ga., said that contact lens makers first started adding color to contacts in the 1970s to make the lenses easier to see. Thats called handling tint, and its put in so that you can see the contact lens when you drop it, Bassett explained. The amount of pigment used to create a handling tint is so slight that it has essentially no effect on how the lens looks on the eye.

By the 1980s, Bassett said, more and more customers were looking for products that enhance the appearance of the eyes as well as vision, and iris-altering contacts were born. Ciba Vision currently makes a dozen different styles of colored contact lenses. Some offer subtle changes, such as lenses that make blue eyes look bluer. Other, novelty lenses can change the eyes appearance dramatically—turning the iris a blood-red color, for instance, or making it look like a cats eye.

The simplest colored lenses are enhancing lenses, which look like a regular contact lens with an iris-sized circle of transparent color. These lenses arent meant to hide the iriss natural color, but rather to augment it. As Bassett put it, its not meant to make a brown eye blue, but to make a blue eye bluer. Ciba Vision creates the color by covalently attaching organic azo dyes to the contact lens polymer.

Ciba Vision makes its sports lenses for athletes in the same way. The dyes used in these lenses, though, are chosen because they absorb certain frequencies of light, enhancing the contrast between a yellow tennis ball and the blue sky, for example, so its easier to keep your eye on the ball, so to speak.

Bassett likened these sports lenses to a filter on a camera. The lenses filter out certain frequencies and let others in preferentially, he said.

Making a more substantial change to the iriss natural color—like making a brown eye look blue—calls for opaque pigments, Bassett said. The unusual and obviously fake look of early colored contact lenses turned off a lot of customers. If you just try to paint over the iris, it looks false, Bassett remarked.

Colored contact makers have gotten better at making dramatic yet realistic-looking changes to the appearance of the iris. Ciba Vision uses sophisticated designs of opaque inorganic pigments to create this type of lens. Bassett also noted that this type of lens isnt just for the fashion conscious. He said Ciba Vision makes custom prosthetic lenses for injured and disfigured eyes.

According to Bassett, the iris designs that Ciba Vision currently uses came from work done at Wesley Jessen, a colored contact lens company now owned by Ciba Vision. Researchers at Wesley Jessen pored over pictures of eyes to identify the features that are common to beautiful eyes. They found that the irises considered most beautiful usually have a dark outer ring, an inner band of color, and a small golden starburst near the pupil.

Ciba Visions FreshLook ColorBlends lenses combine these three features but also have small, uncolored spaces where the iriss natural color shows through. This, Bassett said, gives the lens a more natural appearance.

Nano- and microscale particles of inorganic pigments such as titanium dioxide, iron oxide, and barium sulfate are typically used to achieve the opaque color in these lenses. For certain brands, Ciba Vision adds mica to achieve a pearlescent look. The Food & Drug Administration has approved a very small number of pigments for use in contact lenses, Bassett added.

Although he and his coworkers dont think of themselves as nanotechnologists, Bassett noted that they frequently use nanoscale particles to create colored lenses. When we use pigments, especially inorganic pigments, we need to grind up our particles so that they are small enough not to affect the physical properties of the lens but large enough to reflect color, he said. Bassett pointed out that smaller particles also have less of an effect on the morphology and overall mechanical properties of the lens.

According to Bassett, Ciba Vision employs several techniques to make these opaque lenses. For some lenses, inks are printed directly onto the lens and then covalently fixed onto the polymer surface. Other colored contact lenses are made by putting the inks into a mold and polymerizing the lens around these pigments, encapsulating the color within the contact.

Incorporating pigments into or onto a contact lens may be the most intuitive way to create a colored contact, but it isnt the only way. Dharmendra Jani, a senior engineer in the polymer and surface science group of Rochester, N.Y.-based Bausch & Lomb, spoke about manipulating light to give contacts color.

You would be amazed at how many colors you see around yourself that come from reflected light rather than pigments, Jani said. For example, the vibrant colors of a butterflys wings dont come from pigments, he explained. Rather, they arise from the way light is reflected off the wings surface.

Taking a cue from the butterfly, thin-film specialists at Bausch & Lomb figured they could create films for contact lenses that reflect certain colors of light, thereby changing the apparent color of the iris. The lenses are made by stacking layers of dielectric films of alternating low and high refractive index. This, in combination with the films precise nanoscale thickness, allows the scientists to tailor the lenss reflective properties and therefore its color.

The layers of dielectric film create color through the phenomenon of constructive interference, which works like this: When light strikes something transparent, some light passes through the material and some light is reflected off its surface. If theres a film on that surface, light will reflect off the films surface as well as from the interface where the film and the transparent substance meet. Depending upon the films thickness, a particular wavelength or color will be reflected in phase off both surfaces. The two reflections reinforce one another, amplifying the wavelength so that the surface appears to have a certain color. Other colors are reflected out of phase—this is known as destructive interference—so that all other reflected colors are diminished.

The Bausch & Lomb lenses typically have five layers of thin films with constructive and destructive interference taking place at each interface. This is one application of nanotechnology where, simply by creating thin films, you can create colors where otherwise there wouldnt be color, Jani said.

The films can be made from more than a dozen different compounds, primarily metal oxides, metal sulfides, polymers, and metal halides. Jani noted that the nanoscale films need to be made precisely to ensure that the color is uniform throughout an entire product line. The Bausch & Lomb scientists apply the thin films to the lens using plasma-enhanced chemical vapor deposition or ion-assisted deposition. The process, Jani pointed out, creates a smooth surface on the lens thats imperceptible to the wearer.

Because the lenses are designed to reflect color from incident light coming through the lens from only one side, the contacts color is perceptible only when its on the eye or placed on a dark background. When you hold it in your hand, you see a silver, translucent appearance, Jani said. He also noted that films look transparent on the eye, so the iriss variegated pattern shows through the lens for a natural look.

While colored contact lens makers will undoubtedly continue to use chemistry, physics, and nanoscience to improve their products, Ciba Visions Bassett said that they really hope to make strides in consumer psychology. Right now, we are where hair color was in the 1950s. Lens makers hope that the more natural-looking lenses will make consumers as comfortable with changing their eye color as they are with changing their hair color.

Perhaps the old adage should be revised: Beauty is in the eye of the consumer.