Shifting the Visual Spectrum: 3-dehydro retinol

Because vision is really the primary means by which we assess our environment, throughout history people have always sought ways to augment this ability. Sure, sure. We all know about binoculars and telescopes and microscopes and such... but what if we could enhance our vision without need for any device at all? What if all we needed was a pill? 

George Wald and Freshwater Fish

     American Scientist George Wald was awarded the 1967 Nobel Prize for his contributions to our understanding of the physiology of the eye. Wald and his colleagues had discovered the role of vitamin A in vision. Vitamin A is bound to a protein in our photoreceptors called opsin. Opsin is the light sensitive protein that starts the whole process of phototransduction. There are a few different types of opsin. In rod photoreceptors, we have an opsin called rhodopsin which is very sensitive to the magnitude of light. In cone photoreceptors, we have an opsin called photopsin which is great for detecting different wavelengths of light resulting in color vision. Wald measured the wavelengths of light absorbed by these different opsin proteins and found that a normal functioning human eye can detect light which falls in the spectral range of 390 to 740nm. This knowledge provides us with a greater understanding of the limits of our visual system, and potentially a way to augment it. 

George Wald

     Wald's work was not limited to humans. As a postdoctoral researcher, he worked with many other species and found that not all organisms use the same pigments. Working with fresh water fish, he discovered that their visual pigments were a dark purple color better suited to absorbing light with longer wavelengths. This is because the rods of fresh water fish use an entirely different form of Vitamin A, which he called vitamin A₂. Researchers now called this compound 3- dehydro retinol, but for simplicities sake I'll continue using the much more palatable name A₂. Wald also gave a name to the opsins these fish form with the vitamin A₂. He called it Porphyropsin, from the greek "porphyry" meaning purple.

      At first this division seemed pretty concrete. Sea dwelling fish use Vitamin A and freshwater use Vitamin A₂. But what about fish that are somewhere in the middle? It turns out that the determinant of whether a fish will use vitamin A or A₂ is where spawning occurs. Salmon for example are anadromous. So they live in the sea, but spawn in fresh water and use vitamin A₂. As a result, they have a lower visual spectrum and can see into the Infrared range. Eels on the other hand are catadromous. They breed in the sea and live in fresh water. Thus they use vitamin A and have a visual spectrum similar to ours. Amphibians are even more complex. While in the tadpole phase of life, A₂ is used, but in froggy adulthood vitamin A takes over as the co-factor of choice.

WWII Navy Augments

      During WWII, it wasn't just the Nazis that were performing human research that shuffled over the line of ethics. For example, a group of American conscientious objectors were subjected to long-term vitamin C deprivation. Daily incisions were made on their thighs and the time it took for the wounds to heal meticulously recorded. Another questionable experiment was performed on American Navy men. They were placed on diets free of vitamin A and provided a Vitamin A₂ supplement. According to the textbook "Perception:"

Normally, it is impossible to see infrared radiation because, as pointed out earlier, the wavelengths are too long for human photopigments. In order for humans to see infrared, the spectral sensitivity of some human photopigment would have to be changed. Vision scientists knew that retinal, the derivative of vitamin A, was part of every photopigment molecule and that various forms of vitamin A existed. If the retina could be encouraged to use some alternative form of vitamin A in its manufacture of photopigments, the spectral sensitivity of those photopigments would be abnormal, perhaps extending into infrared radiation. Human volunteers were fed diets rich in an alternative form of vitamin A but deficient in the usual form. Over several months, the volunteers' vision changed, giving them greater sensitivity to light of longer wavelengths. Though the experiment seemed to be working, it was aborted. (Sekuler, & Blake, 1994) 

      The idea was that by eliminating vitamin A, these men's opsin proteins would instead bind with vitamin A₂ making porphyropsin instead of rhodopsin. It appears to have worked. No information is available as to what extent these Navy men's visual spectrum shifted; however, a similar experiment performed by on rats revealed a visual spectrum shift of about 20nm (Yoshikami, Pearlman, & Crescitelli, 1969) .

So how much of a difference is 20nm? Well, since a human's visual spectrum spans about 360nm, this is a difference of only about 5%. Not too promising right? Well wait a minute. Rat's have to be given much credit as a valuable animal in terms of providing us with an understanding of how mammalian physiology works; however, rat's eyes are simply too different for us to conclude that all we can expect is a 5% change. Rat cone cells are Dichromatic, meaning that they see greens and blues pretty well, but can't see reds at all. Humans on the other hand are trichomatic allowing us to perceive green, blues and reds. Rats have even been found to have a novel opsin that gives them the ability to see into the ultraviolet range so this really is a case of comparing apples and oranges. Whereas rats have a system by which to detect UV light, human vision is specialized towards the infrared spectrum and likely far more susceptible to the effects of A₂.

The Sony Nightshot Scandal

So let's speculate for a minute that by eating a diet with no vitamin A, and supplementing with vitamin A₂ we could cause a visual spectrum shift of 50nm, a meager 13% change. How much of a difference is this? In the 90s Sony began producing their Nightshot line of camcorders, which are capable of picking up the infrared spectrum and displaying it in a way we can see. The idea was to have a color camcorder that could be used in the dark just as easily as in the light. Users soon discovered that by running the Nightshot mode in the day, they could see through others' clothing. Sony quickly blocked the Nightshot feature from being able to be activated in high light conditions. 

     Now although human eyes are capable of detecting light waves as long as 740nm, they really aren't that sensitive to it. People looking for alternatives to the discontinued Sony trick found that by simply sticking a 720nm IR pass filter to the front of the camcorder, they once again were free to ogle away. If 720nm is a low enough spectrum light to see through clothing, then our visual spectrum shifted friends' 790nm vision would be just as capable with no apparatus needed. With the ubiquitous nature of nude women on the internet though, one would probably need a greater motivation for taking a potentially dangerous compound than getting a glimpse of their cute neighbor's nipples. Fortunately, there are. A person would be enabled to see through darkly tinted car windows, or sunglasses with ease. Although investigators generally use ultraviolet light to pick up body fluid stains, infrared works just as well. Even old faded papyrus manuscripts and otherwise illegible faded books would be an easy feat for our augmented friend. One limiting factor of how far a person can see is the amount of particulate matter in the air. Infrared light cuts through fog, haze, and dust to a degree that would enable this person to have much sharper vision at a distance than a non-augmented human. One could effortlessly see through makeup and disguises, and perhaps even have an entirely new view of artwork by being able to see the underlying brushstrokes that were later covered. Even more useful would be this person's ability to see in environments too dark for others. Consider the spectrum detected by night vision goggles. Night vision goggles are capable of detecting light wavelengths starting around where the human visual spectrum ends at 740nm and with high end products detecting light as high as 1000nm. A person who could see up to 790nm is about equal to someone wearing generation II night vision goggles. The possibilities are intriguing.

Side Effects and Implementation

     What about side effects you ask? Let me start out with the simple answer of... I don't know. Vitamin A has many other functions in the body. Vitamin A is known to play a role in the human immune system. It's possible that Vitamin A₂ would fill this role seeing as though it can replace vitamin A's role in the eye. Then again it might not, so a person might be more susceptible to infection. Vitamin A also plays a part in epithelial cell growth and repair, so skin problems could arise. Some research has shown that 3-dehydro retinol levels are much higher in patients suffering from hyperproliferative dermatoses such as psoriasis. No indication of these problems was discussed in any of the animal research, but I for one wouldn't take such a gamble without at the very minimum ameliorating the risk by instead implementing a very low vitamin A diet with vitamin A₂ supplements added. A₂ itself isn't any more risky than vitamin A, and we do get small amounts in our diet already, so as long as a person watched their doses closely toxicity is unlikely. There really isn't enough research though to draw any conclusions here. Anyone choosing to self-experiment is assuming a risk, and I'm certainly not advising anyone to give it a try.

The proper dosing for A₂ is be the same as for normal vitamin A. This value falls between 900 and 3000 ug/day for males, and 700 and 3000 ug/day for females according to RDA guidelines. As far as obtaining 3-Dehydro retinol, it can be extracted from the liver of nearly any freshwater fish. It's sold by a few biotechnology supply houses, although they seem reluctant to deal with anyone not employed by a university or biotech research establishment. Yes, I do have a source. The CAS number is 79-80-1, and it should appear as a light yellow crystaline solid. Last time I checked, 2.5mg cost around 300$. This breaks down to around 3 days worth so it's not a cheap experiment. Risks and costs aside, the prospect of extending our senses far outside their normal range is an exciting one. When a person lies, they tend to have a subtle autonomic response. With augmentation, one could perceive the moment when blood is routed to their skin. And we know from research that large regional fluctuations in body temperature occur during different phases of the sexual response cycle, but imagine being able to see these changes as the occur in your lover. For these reasons, I feel this to be augment worthy of consideration.

Works Cited:

Biographical memoirs v.78. (2000). Washington D.C.: National Academy of Sciences.

Sekuler, R, & Blake, R. (1994). Perception . McGraw-Hill Humanities/Social Sciences/Languages.

Yoshikami, , Pearlman, , & Crescitelli, . (1969). Vision Research, 9, 633-643.