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Your Prion Eyes

BioPhotonics
Oct 2010
Lynn Savage, Features Editor, lynn.savage@photonics.com

When you gaze into someone’s eyes, you can tell much about their character. It just so happens that you also might be able to tell whether they have a neurological disease.

Jacob W. Petrich and his colleagues at Iowa State University in Ames have shown that basic noninvasive fluorescence spectroscopy can show whether animals have been infected with a form of transmissible spongiform encephalopathy (TSE). Experienced by cows as bovine spongiform encephalopathy (BSE, aka “mad cow disease”) and by sheep and goats as scrapie, TSE is a neurodegenerative disease that slowly destroys the brain via the growth and aggregation of protein-laden structures called prions.


Hyperspectral fluorescence images can reveal whether an animal has a form of transmissible spongiform encephalopathy. Shown are the retinas of sheep that are scrapie-free (A) and those that have scrapie (B). Courtesy of the American Chemical Society.

An incurable malady related to Creutzfeldt-Jakob disease, BSE can be transmitted from cattle to people, especially if infected cow brains and spines are allowed to mix into the human food supply.

Using spectrofluorometry and hyperspectral fluorescence imaging microscopy, Petrich’s team examined the eyeballs of several dozen sheep, looking for evidence of scrapie in both infected and noninfected beasts. After observing the spectra emitted from the various parts of each eyeball, the researchers found that both the retina and the sclera (the protective tissue that covers most of the eye) showed large differences in fluorescence intensity and other spectral features between healthy and nonhealthy tissue.

The group’s members do not yet know the precise cause of these differences, but they suspect that the prions cause an increase in a lipid-rich material called lipofuscin, which allows the eyes to become a window to neurological well-being.


GLOSSARY
fluorescence
The emission of light or other electromagnetic radiation of longer wavelengths by a substance as a result of the absorption of some other radiation of shorter wavelengths, provided the emission continues only as long as the stimulus producing it is maintained. In other words, fluorescence is the luminescence that persists for less than about 10-8 s after excitation.
retina
1. The photosensitive membrane on the inside of the human eye. 2. A scanning mechanism in optical character generation.
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