New lenses allow colorblind to see brilliant color

Writer
Graduate Division

Red/green colorblindness is a genetic, X-linked trait that affects upward of 7 percent of the male population in the U.S. While it usually does not pose serious restrictions to daily life, there has never been a way for those affected to experience red and green colors—until now.

Enchroma, a Berkeley-based company, recently unveiled a new device that uses color-blocking lenses to force the separation of red and green colors for those with red/green colorblindness. When you look at the technology behind their breakthrough, it starts to look very familiar.

Our eyes respond to the presence of light via light-sensitive proteins that activate a retina cell when they are hit by photons. The retina of the eye contains rod and cone cells, which help to see light/dark and color, respectively. Cone cells contain three different types of light-sensitive proteins, or opsins, that respond to different colors of light. Each cone cell expresses only one type of opsin, meaning that we have “red,” “green” and “blue” cones. When blue light hits the opsins of a blue cone, it initiates a signaling cascade that ultimately sends a signal to the brain that blue light was seen by that cone in that specific part of the retina.

Blue opsins respond to the highest energy wavelength of light (420–444 nanometers) and are found in short cones, green opsins respond to 534–545 nanometer light and are found in medium cones, and red opsins in long cones respond to light of 560–584 nanometers in length.  

The discovery and study of opsins, rods and cones won three scientists a Nobel Prize in 1967. In the most common form of red/green colorblindness, known as deuteranomaly, the green opsin expressed in medium cones is slightly mutated. While the protein is still expressed normally in the cell, it now responds to wavelengths of light closer to the 560–584 nanometer range. For these individuals, it becomes difficult to distinguish red and green colors because the two different types of cone cells are now responding to very similar wavelengths of light. However, while the mutated green opsin responds much more efficiently to yellow/orange light, it can still respond to green light—albeit at a much lower efficiency compared to the wild-type allele.

Enchroma’s Cx sunglasses use this information to generate a pair of lenses that force your eyes to see only tight, small ranges of wavelengths of light in the blue, green and red colors by making what are commonly referred to as “interference lenses.” Interference lenses, like regular mirrors, reflect light. However, what makes them special (not to mention expensive and hard to manufacture) is that they reflect most light, but allow a certain range of wavelengths to pass through.  

The beautiful simplicity of Enchroma’s technology is that by using interference lenses, they can force incoming light to become restricted only to the three individual ranges of wavelengths (420–444, 534–545 and 560–584) that are detected by our eyes. For those with regular color vision, Enchroma lenses do not significantly alter the appearance of color. For those with deuteranomaly, the mutated green opsin—which would normally respond to more yellow and orange wavelengths of light—can respond only to light in the truly green 534–545 nm range because the yellows and oranges have been blocked by the interference lens. What used to look green/red is now only green, resulting in a dramatic change in the visual perception of color. Colors look vibrant and there is no loss in the variety of colors you can see, because it’s the combination of red, green and blue that makes up our visible spectrum. Because the lenses restrict a significant portion of incoming light,  though, it is recommended that they be used only in bright sunlight.

Given the prevalence of interference lenses in biomedical imaging, it may be surprising to learn that not any of the founders at Enchroma began as optical biologists. It may also be surprising that it has taken this long to repurpose interference lenses as glasses. In fact, interference lenses have been incorporated into glasses before as anti-reflective coatings. The trick to Enchroma’s technology that makes it so special is the combination of thin-layer coatings that restrict three unique ranges of light (red, green and blue) without completely blocking incoming light. Similar combined “band-pass” filters for microscopy—which accept only discrete red, green, blue and UV wavelength ranges—have only recently been developed for research.

For scientists with a background in imaging or flow cytometry, interference lenses are nothing new. Early naturalists in the 1800s made dichroic mirrors by coating glass with heavy metals such as lead or cadmium. By putting the glass up to the light, scientists noticed that while some wavelengths of light were reflected (hence the glass looking like a mirror), some light would get through, leading to a colored tint to the mirror and a shadow in a specific color. These materials, however, went largely unused until the advent of fluorescent technology in the 1960s.

Flow cytometers are machines that take up samples of cells in liquid suspension and let them flow, one-by-one, past lasers that shoot a specific wavelength of light through the cell. If the cell has a dye on it that responds fluorescently to that wavelength of light, the cytometer’s detector makes a note of the response’s intensity. Cells can be treated with many different types of dyes and markers that respond with slightly different spectra of fluorescence to one laser’s wavelength. To separate these different spectra and allow a cytometer to identify many different types of markers on each cell, light that passes through each cell goes through a series of interference lenses that siphon off each range of fluorescence, one by one, until each color can be separated and quantified. Fluorescent microscopes behave in a similar way, but with usually only three or four interference lenses, allowing for the imaging of cellular fluorescence into a UV, green, red and blue channel.

Enchroma’s Cx lenses will not cure colorblindness, but the results are still breathtaking. Astonishing, too, is the simplicity of the technology behind the breakthrough. For more information on Enchroma Cx, visit www.enchroma.com