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.
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 andother
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
andaphakic 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 June 11, 2009
return to Stark home page
