I am especially interested in human visual sensitivity to UV light. Most people do not see UV light because the lens absorbs UV. After cataract surgery, a condition called aphakia, "near" UV light (300 - 400 nm) can reach visual receptors. My interest stems in part from my own condition of being aphakic in one eye. There was surprisingly little information about human UV sensitivity though the topic was becoming increasingly relevant in view of the mounting evidence for UV damage to the vertebrate retina. Using traditional psychophysical methods, I determined the photopic (cone) spectral sensitivity into the UV portion of the spectrum and determined the UV absorption by the macular pigments, carotenoid screening pigments in front of the fovea. I compared the scotopic (rod) spectra of aphakic observers and normal subjects and deduced the UV absorbance of the lens. I used chromatic adaptation to show that individual cone types were more sensitive to UV light than expected on the basis of their resident rhodopsins. What does UV light look like? Actually, it looks a desaturated (whiteish) blue. My demonstration of this is a Blak-Ray (UVL-56) lamp where I have replaced the filter with Corning filters #5840 (7-60) [UV] and #5330 (I-64) [blue] -- these both look the same to my aphakic eye. I speculate that UV looks whitish blue because all three cones are sensitive to UV light but that the blue cone is especially UV sensitive.
The
original intraocular lens implants transmitted near UV, but in about 1988, UV
blocking was used regularly. These lenses were polymethylmethacrylate.
In 2011, Alek O. Komarnitsky
contacted me with a wonderful web site
documenting his ability to see UV through Crystallens
brand implants.
On the side, I was interested in how to take photographs in the UV. Already,
there had been numerous published photographs to dramatize how different
flowers would look in the UV to their insect pollinators. When my son was in
junior high school, and I was the dad, I helped Dan with a science project to
determine feasibility. With a Corning filter for near-UV (300-400 nm) in front
of the camera, we found that the ASA (ISO) of Kodak 2415 Technical Pan film
(developed in Kodak HC110 at dilution D) is very fast (about 6400). That means
that if you have enough UV light, your camera light meter will probably work
and not be very far off if you set it at the film's nominal ASA (400). Here is a photograph I took of
the flower of Zygadenus nuttalii (UV
light on the left and white light on the right) in a
collaboration (P. Bernhardt, Chap. 9 Anther adaptation in animal
pollination, in W. G. D'Arcy & R. C. Keating, The Anther, Form Function and
Physiology, Cambridge University Press, New York, 1996). For these photographs,
I used a Nikon F camera and a Nikkor 55 mm lens. For
UV illumination, I used GE F15T8 BLB "black" lights, high in the
300-400 nm range, and a time exposure of about 30 s was necessary. These days,
virtually nobody uses film. Here
(right) is columbine in UV light. A white light photo is in the middle, and a
digital camera snap shot from my garden is on the left. Note that the yellow,
as well as the red are fairly dark to UV. Here is my rhododendron,
again with yellow being UV-dark. And here is catalpa. Methods -- A MTI CCD 72 camera
and a Fujinon TV 1:1.7/35 lens (and a flower) are
under a bank of UV lamps (right); computer and monitors are on the left; see this paper for image capture
details.
Memoirs
Because of a traumatic cataract I had when I
was 10, and surgerry when I was 12, I could see UV
light, and that proved very convenient with my interests in Drosophila UV
vision. In the 1970's, I noted that there was very little literature on human
UV vision. I met Charles White who showed me a very thorough study, a
dissertation by Karel E.W.P. Tan from Utrecht. I
wondered why it had not been published, so I called Mat Alpern
(Tan's mentor) and Dan Green at the University of Michigan. They said the work
was wholesome but that Tan had lost his "publish or perish"
motivations because he was a clinician. I contacted Tan and we agreed to
publish a comparative review of UV vision. It was later, 1982, that I met Karel in Utrecht. At the time it was published, there was
little work on vertebrate UV vision, but soon after that, the dam broke and
there was a flood of work on fish, birds and other vertebrates. Soon after I
brought De-Mao Chen from Shanghai for a brief post-doc, he worked on birds with
Tim Goldsmith at Yale. Chen later returned to my lab and worked with me for 8
years. I went up to Montreal twice to work with Charles White in preparation
for the human psychophysics work I published in the late 1980s and early 1990s.
My papers on human UV vision:
Stark, W.S. and Tan, K.E.W.P. Ultraviolet light: Photosensitivity and other
effects of the visual system. Photochemistry and
Photobiology, 1982, 36, 371-380. (Invited review to accompany American
Society for Photobiology1981 Meeting Lecture). PubMed
Stark, W.S. Photopic sensitivities to ultraviolet and
visible wavelengths and the effects of the macular pigments in human aphakic observers. Current Eye
Research, 1987, 6, 631-638. PubMed
Griswold, M. S., Stark, W. S. Scotopic spectral
sensitivity of phakic and aphakic
observers extending into the near ultraviolet. Vision
Research, 1992, 32, 1739-1743. PubMed
Stark. W. S., Wagner, R. H., Gillespie, C. M., Ultraviolet sensitivity of three
cone types in the aphakic observer determined by
chromatic adaptation. Vision
Research, 1994, 34, 1457-1459. PubMed
Two science features that relate to my interests:
Ivan Amato, Birds-eye view, Fortune, 2005, on
line
David
Hambling, Let the light shine in (you don't have to
come from another planet to see ultraviolet light), The Guardian, Thursday, May
30, 2002, on
line
The yellow
lens blocks UV vision in people. These fresh lenses from the eye bank are from
79 year old (top) and 39 year old (bottom) donors.
The lens absorbance inferred by
subtracting the scotopic (rod) spectral sensitivities
of normal from aphakic (lensless)
observers (from Griswold and Stark, 1992)
Here is a handsome 38 year
old subject participating in the psychophysical study published in 1987
Here are human aphakic cone photopic
sensitivities on fovea vs off fovea. The difference
centered around 460 nm is due to the macular pigments.
Here are scotopic
sensitivities from aphakic and normal observers. The
difference in the UV is due to the lens.
Short, middle and long
wavelength cone spectra were determined by spectral sensitivities against
chromatic background. Short and long wavelength cone spectra are much higher in
the UV than expected from a rhodopsin with a cis peak.
Why UV looks a desaturated blue. Tan's data (left)
and the color diagram (right). Violet to red traced clockwise around the
horseshoe, white inside. Wavelengths below 400 nm trace
toward the white and blue. This relates to the previous figure showing
that all three cones are UV sensitive, especially the blue cone.
Here are
Monet's water lillies at Giverney
painted before (left) and after (right) his cataract surgery
This page was last updated on August 1, 2012
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