Washington ? Space shuttle science may soon come to an eye doctor near you: Researchers are using a NASA gadget to finally tell if a cataract is brewing before someone’s vision clouds over.

It’s a story of shot-in-the-dark science that paid off with a noninvasive test that tells when eyes are losing the natural compound that keeps cataracts at bay.

That brings the potential to fight the world’s leading cause of vision loss. Knowing their eyes are vulnerable could spur people to take common-sense steps to reduce that risk, like avoiding cigarette smoke, wearing sunglasses and improving diet.

More intriguing, the device allows easier testing of whether certain medications might prevent or slow cataract formation. Studies involving astronauts — whose space flights put them at extra risk — and civilians could begin later this year.

Don’t call the eye clinic yet: The government has only a few prototypes of the device and no commercial manufacturer lined up. But already, doctors at Baltimore’s Johns Hopkins University have begun experimental use to see how the exam might fit into the care of a variety of eye patients.