Eat Your Carrots! The Chemistry of Vision


18th-century hand-colored etching of woman pushing wheelbarrow full of carrots.

“Sandwich Carrots-Dainty Sandwich Carrots.” Hand-colored etching. Gillray, James, 1756-1815, engraver. Published by H. Humphrey, 1796 Dec 3d, London.
Image courtesy of Library of Congress.

You’ve probably heard the old adage about eating carrots for good vision. Well, there is some truth to it. Carrots contain a high concentration of β-carotene which gets broken down in the intestines to form the aldehyde (hydrocarbon) form of vitamin A, cis-retinal. Vision deteriorates in the absence of vitamin A because cis-retinal is trafficked along the protein, opsin, to produce electrochemical signals from light.

Our retinas perceive light in tiny particles called photons. As soon as these photons hit the retina, they isomerize cis-retinal to trans-retinal.  Trans-retinal then bonds to opsin to form rhodopsin. Rhodopsin is a purple pigment in the photoreceptor cells of the retina that reads blue-green light. This is the first step of the phototransduction cycle where photon energy is transferred to a series of signaling and diffusing protein complexes.

Retinal isomerism drawn with ChemDraw

Mutated forms of rhodopsin will be folded and transported differently and could lead to deteriorated vision or blindness. In more rare cases, mutations can cause rhodopsin to be constantly activated, even in the absence of light. Hypersensitivity, autoimmune disorders, and mutations can all cause rod cells in the retina to undergo apoptosis or cellular self-destruction. This sort of degradation of the retina will ultimately lead to deteriorated vision and eventually blindness.

The absorbance of cis-retinal is optimized at approximately 100 nanometers less than rhodopsin and it is a very rigid molecule because of the arrangement of its double bonds. Thanks to isomerism, we can see in color as opposed to ultraviolet! As all of the above demonstrates, our ability to see involves a series of complicated and precisely regulated bio-chemical processes, and carrots play their role.

We will be exploring more about vision loss and blindness in the upcoming GLIMPSE issue 10, Blindness. In the meantime, let us know your thoughts, research, questions, or experiences related to the topic.

If you’re interested in the chemistry of vision and why we perceive the section of the electromagnetic spectrum that we do, you might also be interested in GLIMPSE, issue 4, Color, and the article on “Human Potential for Tetrachromacy” by Kimberley A. Jameson and the online supplementary article.


Myya McGregory is the GLIMPSE 2012 Science Writing Intern. She is a junior double-majoring in chemistry and economics at Williams College. She enjoys music, dance, and literature.

Newly discovered! The earliest color motion pictures

Lying dormant in the archive of Britain’s National Media Museum for decades, what everyone thought were black and white films, turned out to be the first color motion pictures ever made. British photographer Edward Turner made the films using his 1899 patented color film process in about 1903, shortly before his untimely death:

A complicated process, it involved photographing successive frames of black-and-white film through blue, green and red filters. Using a special projector…these were combined on a screen to produce full-colour images.

Highlights of these never-before-shared test films can now be seen on YouTube via our 21st-century RGB screens, and of course, at the museum itself, where the specially-formatted projector can be viewed as well.

Thanks to GLIMPSE subscriber, Francis H., for sharing this with GLIMPSE readers! A very well-timed discovery with our Cinema issue.

Che Guevara: Life after Death Part 1

Che Guevara mural in Havana from Library of Congress Archives

by Myya McGregory

Chevolution” is a documentary on Che Guevara and the journey of his iconic image. The film makes the case that Che was not only an important figure in the history of Cuba and revolution but also in the history of photography and art.

Che was an Argentine doctor who left his middle class life to join the fight against poverty and corruption being waged by guerilla regiments across South and Central America. Scholars say he was strongly motivated by the rampant poverty he witnessed in his travels. With his interest in Marxism it was no surprise that Che would end up joining Fidel Castro’s “Movimiento 26 de Julio” to take down the long reigning Batista regime in Cuba.

Che was a very well liked figure. He was charismatic, skilled in combat, intelligent, he led by example, and he was the type of activist that Cuba needed at the time.

While aiding in a Bolivian rebellion against Rene Barrientos Ortuño in 1967, Che was killed  by a group of CIA trained guerilla fighters.

Che’s life was profoundly influential in Latin American politics, and his legacy in the arts also continues to intrigue.

A lover of  photography himself, Che insisted on documenting every step of the revolution. When he attended a mass memorial for victims of a terrorist attack at the Plaza de Revolución, Alberto Korda, fashion photographer extraordinaire, snapped the iconic image that would travel around the world inciting revolution in ways that Che could have only imagined.

At the time the Leica M2 was one of the best cameras on the market. Made by a German optics company, the Leica M2 used regular 35 mm film, groundbreaking parallax compensation, and focal-plane shutter.

Leica M2 from Flickr by Shane Lin

Using celluloid film (which had been around for almost a century at that point) and homemade developing solution, Korda and the other photographers traveling with Che would develop, enlarge, and print their own images.

Che came along in a time when photography was becoming more public. Nitrate based celluloid film was no longer commercailly available by the early 1950s because it was highly flammable and toxic. In fact the Northeast Document Conservation Center points out that because cellulose nitrate was so unstable, many of the images taken on this film have deteriorated drastically. It is more likely that Korda took his iconic photo using 35mm acetate based celluloid film. Cellulose acetate was considerably less toxic that cellulose nitrate however its decomposition was equally as autocatalytic and just as caustic (it would produce vinegar as a byproduct in decomposition). Luckily for Korda, copying negatives of photos was a relatively simple process and creating an interpositive could lessen the risk of diluting the image quality along the way. It seems that Che  lived at just the right time in photographic history.

How would history would have changed if Che arrived in different place along the photographic history timeline? What about other leaders and cultural/historical icons?

Movement, Orientation, and the Brain

The Mental Mechanics of Motion

Suzanne Farrell and George Balanchine in Don Quixote from the Library of Congress Archives

by Myya McGregory

George Balanchine, New York City Ballet master choreographer, once said, “see the music, hear the dance,” implying that dance is felt. Anyone who has ever attempted any type of movement that could be considered dance has probably been told to “feel the music” or perhaps “stop thinking and just move,” which can be frustrating, since in order to disconnect one’s brain, it must first be engaged. Learning new movements is not necessarily an easy task. Those who do it well make it look easy, but everyone goes through the same mental mechanics.

Here is where the production of γ-aminobutyric acid or GABA comes in. GABA is a neurotransmitter that is produced from the decarboxylation of glutamate in the brain.

GABA from the NIST database

Levels of GABA in the motor cortex play a large role in the development of our motor function and how we learn movement sequences. Studies in Current Biology by Stagg, Bachtiar and Berg have shown that the degree of motor learning and a decrease in the the magnitude of GABA are positively correlated. That means that the degree of short-term motor learning increases as GABA levels decrease in the motor cortex. As we try to learn motor functions, we engage the cerebellum which produces the enzyme catalyst that helps turn glutamate, the neurotransmitter that excites our neurons and helps us learn, into GABA which in turn inhibits neural activity.

Streeter et al. conducted a subsequent study that pinpoints what type of activity can increase our GABA levels. His team used magnetic resonance spectroscopy to monitor the levels of GABA in two different participant groups. One group was actively engaged in walking for sixty minutes three times a week for twelve weeks. The other group dedicated that same time to yoga. They found that subjects who participated in yoga had higher levels of GABA in the thalamic system overall. Yoga experts experienced a GABA increase of 26%. Those that were yoga beginners experienced a 13% increase. As you try harder to learn, your brain works to help mitigate GABA, but it’s these increased levels of GABA early on that make the initial learning curve the steepest.

GABA, however, is not completely bad, since it also boosts our mood and helps relieve stress. Therefore, the more you know, the more you can relax and in this case enjoy the calming benefits of yoga.

So next time you’re struggling in a dance class (or a yoga or zumba class, or struggling with any movement based activity for that matter), know that it gets better if you just stick with it — the secret’s in the GABA.

Pioneers of Color Photography

The history of color photography features many key players and pioneers. In anticipation of the Cinema Issue, GLIMPSE is taking a brief look at some of them, and their contributions to the world of photography.

Paris, France 1864

Louis Ducos du Hauron, a French physicist, developed a motin picture device in 1864. In 1869, he patented a series of practical methods of color printing based on the tri-color theory and the heliochrome system. Using a series of filters, he was able to print color photographs by printing the negatives on sheets of bichromated gelatin that were complementary colors of the negatives themselves. When the positive images were superimposed over the negatives, the resulting image was in color.

Meanwhile, Charles Crocs, another French physicist, developed the similar process in his physics lab. Unfortunately he published his findings 48 hours after de Hauron patented his.

London, England 1861

James Clerk Maxwell, prominent physicist and mathematician, projected a color photograph through a series of filters to show a photograph of the original image in its original color.

West Kill, New York 1851

Levi Hill, an American minister, claimed to be the father if color photography. He presented what he claimed was the first color photograph while experimenting in an early photographic process known as the “daguerreotype.” Hill failed to patent his eponymous “Hillotype” process but did not give up on what he discovered, making a series of Hillotype photographs in color.  Over 160 years later, the Smithsonian Institution now boasts a collection of 62 Hillotypes that have been under severe scrutiny. Using spectroscopy the Smithsonian Institution has finally given substance to the myth. It was found that though Levi Hill enriched his photographs with a series of chemical pigments, the photographs the he produced were in fact faint color photographs.

How about it, all you photographers/photo-appreciators? Who are your favorite historical heros of color photography?

40,000-Year-Old Art is Alive and Well

Photograph courtesy of member Paul Mannix

Researchers have made an interesting discovery about ancient rock art in Western Australia: it’s alive. While most rock art fades over time, the colors on these caves have remained bright and vibrant after an astonishing 40,000 years. How did this happen? ‘Living pigments,’ the term dubbed by the researchers to explain this phenomenon. The pigments of the original painting were eventually replaced by pigmented microorganisms. These microorganisms have replenished themselves countless times over the years, resulting in the artwork’s brightness. Whether or not the artists knew their pigments would survive is unclear, but in a world where the passage of time generally decays, breaks down, and rusts relics of the past, it’s fascinating (and refreshing) to see that every so often, time is on our side.

Allison Nonko

Mama Don’t Take My Polaroid Away

Much like the American singer/songwriter Paul Simon who crooned nostalgic over visual technology in his 1970s hit “Kodachrome,” Austrian entrepreneur Florian Kaps is making his own case for keeping the Polaroid camera alive in today’s visual market.

Wall Street Journal writer Eric Felten in “It’s Baaaaack! But Polaroid Film Was Just Lucky” describes Kaps’ tenacious journey to save the Polaroid from utter oblivion—from begging the junk men not to destroy the last functioning Polaroid factory machines outside of Amsterdam while he vigorously raised money to save them, to putting together a team of scientists to come up with a new sepia-toned black-and-white film that could be used in standard Polaroid cameras (the arcane chemicals originally used to run in the machines could no longer be produced).

What’s resulted from Kaps’ valiant efforts to preserve a medium that we often associate with the psychedelic, saturated ’60s (although it was invented in 1929) is The Impossible Project. It’s a website that allows individuals around the world to peruse and purchase classic Polaroid cameras with modern twists, and also a wide variety of analog instant film.

The Glimpse team gives kudos to Kaps for preserving a nearly extinct perspective, and for keeping the dialogue between new and old visual technology alive and well.

Above image titled “Enschede5.” ©The Impossible Project