NASA astronaut Michael Lopez-Alegria flew to space four times for the space agency between 1995 and 2007.

While in space, his eyesight deteriorated, a well-documented medical issue NASA's known about for years, and one that many astronauts have experienced first-hand. For many astronauts, their eyesight readjusts once they get back to Earth.

That wasn’t the case for Lopez-Alegria, though. His eyesight got significantly worse during his time in orbit, and NASA isn't paying for his contacts or doctor visits today, years after his retirement from the agency.

However, he still travels to Houston, Texas once per year to allow the agency to gather data about his health, without any expectation that NASA will offer treatment for any conditions that may have developed because of his time in space.

In other words, while Lopez-Alegria's eyesight deteriorates, NASA benefits from the data he provides to the American space program, without medical recompense to him today.

The lack of health care for former astronauts has long been a sore spot at NASA, but now it threatens the agency's future. Deep space missions beyond the moon, like a mission to Mars, require a better understanding of how extended spaceflight affects the human body.

To figure that out, the agency needs as much data as it can get its hands on. But without NASA-provided health care, former astronauts have a limited incentive to keep returning to a NASA doctor for a checkup.

All that should change soon, however, with the passage of a bill that would allow NASA to provide health care for former astronauts.