Eyes Flatten in Space: How NASA Came to Allow Contact Lenses
1959.
NASA asked the military for names to fill its first astronaut class.
The requirements: jet flight experience and engineering training.
And a height of no more than 5 feet 11 inches, about 180 cm.
Not because of the spacecraft. Because of the seat inside it.
Five hundred candidates. Seven remained.
All seven were military pilots.
So none of them had bad eyes.
For decades afterwards, the impression stuck: an astronaut must have perfect eyesight.
Read today's NASA rules, though, and the story is different.
Today's standard: correctable to 20/20
NASA publishes the physical requirements for astronaut candidates.
The vision line is one sentence.
"Distant and near visual acuity must be correctable to 20/20 in each eye."
Correctable.
Glasses or contact lenses — if you see 20/20 with them on, you pass.
The same document lists the other conditions: blood pressure no higher than 140/90 seated, standing height between 62 and 75 inches (about 157–190 cm).
The height rule looks stricter than the eye rule.
Refractive surgery such as LASIK and PRK is also permitted, on NASA's guidance that at least a year has passed with no lasting side effects.
In other words, there are astronauts who wear glasses, and astronauts who wear contact lenses.
Contact lens materials were tested on the Space Shuttle
NASA's relationship with contact lenses did not stop at "permitted."
Between 1993 and 1996, the Space Shuttle carried a contact lens experiment three times.
STS-57 Endeavour, STS-63 Discovery, STS-77 Endeavour.
It was a joint project between an Arizona lens company, Paragon Vision Sciences, and NASA's Langley Research Center.
The subject: oxygen-permeable polymers — the material of rigid lenses.
When you synthesise a polymer on Earth, convection keeps the chains from growing evenly.
In microgravity there is no convection.
So researchers could see clearly "which ingredients make the material uneven and reduce oxygen permeability."
That result came back down to the factory floor.
Two products followed.
One was a rigid lens material with high oxygen permeability, called HDS.
The other was CRT, a lens you wear overnight so that myopia is temporarily reduced during the day — the first lens of that kind (corneal refractive therapy) to receive FDA approval. NASA records that nearly 70% of trial subjects reached 20/20 or better.
A space experiment became a lens on Earth.
But stay in space long enough, and the eyes change
Here is the heart of this story.
In 2011, a paper appeared in the journal Ophthalmology.
A team led by Thomas Mader compared the eyes of seven astronauts before and after long-duration missions.
Three findings.
The back of the eyeball flattens.
The optic nerve head swells.
The prescription shifts toward farsightedness — by +0.50 to +1.75 dioptres.
The condition was given a name.
SANS: spaceflight-associated neuro-ocular syndrome.
The leading explanation is fluid shift.
On Earth, gravity pulls blood and fluid toward the legs.
In microgravity, that fluid rises toward the head.
Pressure inside the skull redistributes, and it presses on the back of the eye.
An eyeball that gets shorter front-to-back pushes the focal point behind the retina.
That is a shift toward farsightedness.
How common, and does it go back
Among long-duration astronauts, about 15% show clinically significant swelling of the optic nerve head.
With precise imaging (OCT), some degree of change shows up in nearly all of them.
The good news: no permanent vision loss has been reported so far.
Every affected astronaut could still be corrected to 20/20.
Some, however, carried prescription changes for several years after returning.
NASA classifies this as a major risk for long missions such as Mars.
So the space station carries "glasses made in advance"
There is no treatment yet.
There is a precaution.
Before launch, astronauts pack "space anticipation glasses."
Reading-type glasses made in advance, calculated for the expected farsighted shift.
It is the same principle as the ADD line that appears on your prescription when presbyopia arrives in your forties. On Earth, age pushes the focal point; in space, microgravity does.
Presbyopia and ADD are covered in At 43, the Restaurant Menu Suddenly Moved Away.
In the end, the answer is the same
In space and on the ground, the conclusion fits in one line.
If the eyes change, correct them.
NASA does not require perfect eyes.
It requires correctable eyes.
And when it knows the eyes will change, it packs the glasses first.
Not so different from putting a spare box of lenses in your travel bag.
References
- NASA, Astronaut Selection and Training (NASA Facts) — vision, blood pressure and height standards; the 1959 selection
- NASA Spinoff 2004, 'Contact' in Space Leads to New Lenses — STS-57/63/77 experiments, HDS and CRT
- Lee AG et al., Spaceflight associated neuro-ocular syndrome (SANS) and the neuro-ophthalmologic effects of microgravity, npj Microgravity 2020 — the 2011 report, dioptre range, the 15% figure
- NASA Glenn, Spaceflight Associated Neuro-Ocular Syndrome
- Eye (Nature) 2024, Refractive shifts in astronauts during spaceflight — space anticipation glasses
This article provides general information. NASA updates its astronaut selection criteria from time to time; the figures here are as of the referenced publications. If you notice a change in your vision, seek an eye examination regardless of the cause.