**A Missile in Your Eye**

by Patrick L. Barry

Satellite technology designed to catch ballistic missile launches may
soon help doctors monitor the health of people\'s eyes.

For the last 15 years, Greg Bearman and his colleagues at JPL have been
working on a novel design for a spectrometer, a special kind of camera
often used on satellites and spacecraft. Rather than snapping a simple
picture, spectrometers measure the spectrum of wavelengths in the light
coming from a scene. From that information, scientists can learn things
about the physical properties of objects in the photo, be they stars or
distant planets or vegetation on Earth\'s surface.

In this case, however, the challenge was to capture snapshots of
short-lived events---like missile launches! The team of JPL scientists
designed the new spectrometer, called a computed tomographic imaging
spectrometer (CTIS), in collaboration with the Ballistic Missile Defense
Organization as a way to detect missiles by the spectral signatures of
their exhaust.

But now the scientists are pointing CTIS at another fast-moving scene:
the retina of an eye.

Blood flowing through the retina has a different spectral signature when
it is rich in oxygen than when it is oxygen deprived. So eye doctors can
use a spectrometer to look for low oxygen in the retina---an indicator
of disease. However, because the eye is constantly moving, images
produced by conventional spectrometers would have motion blurring that
is difficult to correct.

The spectrometer that Bearman helped to develop is different: It can
capture the whole retina and its spectral information in a single
snapshot as quick as 3 milliseconds. \"We needed something fast,\" says
Bearman, and this spectrometer is \"missile-quick.\"

CTIS is even relatively cheap to build, consisting of standard camera
lenses and a custom, etched, transparent sheet called a grating. "With
the exception of the grating, we bought everything on Amazon," he says.

The grating was custom-designed at JPL. It has a pattern of microscopic
steps on its surface that split incoming light into 25 separate images
arranged in a 5 by 5 grid. The center image in the grid shows the scene
undistorted, but colors in the surrounding images are slightly "smeared"
apart, as if the light had passed through a prism. This separation of
colors reveals the light\'s spectrum for each pixel in the image.

"We\'re conducting clinical trials now," says Bearman. If all goes well,
anti-missile technology may soon be catching eye problems before they
have a chance to get off the ground.

Information about other NASA-developed technologies with spin-off
applications can be found at <http://www.sti.nasa.gov/tto> .

This article was provided by the Jet Propulsion Laboratory, California
Institute of Technology, under a contract with the National Aeronautics
and Space Administration.

![](media/image1.jpeg){width="6.0in" height="3.7354166666666666in"}

Caption:

*This three-color composite image from the computed tomographic imaging
spectrometer shows the oxygenation of the blood in the arteries and
veins of a human retina. (Arteries appear red, veins appear yellow.)*

*Note to editors: this image may be found at
<http://spaceplace.nasa.gov/news_images/retinal_oximetry.jpg> .*