Blurred vision in space: 70% of astronauts face eyesight problems due to space travel, says NASA

NASA astronaut Sunita Williams performs an eye exam while wearing a cuff on her left leg. (Image: NASA)

For most people, a long journey brings tired eyes. But for astronauts, space travel can bring lasting vision changes—and scientists are now trying to figure out why.

Sight Shift in Space

NASA has found that almost 70 percent of astronauts on long missions report changes in their eyesight. The issue doesn’t just vanish after landing. Some effects can last for years.

Dr. Sarah Johnson first noticed the problem after her six-month stay on the International Space Station. Text that was once sharp had become hard to read. Other crew members have reported similar problems—blurred distance vision, trouble focusing, and pressure behind the eyes.

NASA now calls this condition Spaceflight Associated Neuro-ocular Syndrome, or SANS. Unlike motion sickness or weak muscles, this problem doesn't always improve once back on Earth. That has made it one of NASA’s most serious health concerns for deep space travel.

Pressure Where It Shouldn’t Be

Scientists believe the real cause lies in weightlessness. On Earth, gravity pulls body fluids downward. But in space, those fluids shift upwards, leading to puffier faces and extra pressure in the skull.

This pressure can push on the back of the eyeball. It may also swell the optic nerve, altering how astronauts see. These changes could become a serious risk on future Mars trips, which may last up to three years.

Dr. Michael Roberts, who leads NASA’s vision research, says the stakes are high. “If eyesight keeps worsening in space, a mission could fail.”

Testing Ways to Help

NASA is now testing solutions to protect astronauts’ eyes. That includes special contact lenses, medicine to reduce fluid buildup, and fitness plans that support blood flow.

One new tool is the VIIP chamber. It creates Earth-like pressure around the head, which might help ease the stress on the eyes.

Though the problem starts in space, this work could help many on Earth too. The findings may improve treatment for glaucoma and other pressure-related eye issues.

As astronauts reach farther into space, vision may remain one of the biggest hurdles. But NASA hopes their eyes will adjust in time to clearly see Mars—and beyond.