University of Otago department of medicine ophthalmologist researcher Dr Francesc March has spent much of the past two years flying in a plane to great heights above France, and then flying down again at such a rate of descent that everyone on board is exposed to zero gravity.
It is used by astronauts for zero-gravity training and is often referred to as "the vomit comet".
But Dr March has been using the flights to study how human eyes are affected by microgravity — particularly dry-eye disease (DED) in space-like conditions.
It is the first research of its kind.
"We use parabolic flights, which create short periods of microgravity through precise flight patterns, as a precursor to orbit-based research."
He said DED was a significant ocular issue which caused eye irritation, strain and blurred vision.
"It impacts the layers of tears that cover your cornea and occurs when you either don't have enough tears or when they evaporate too quickly."
He said it affected about 15% of the population. There was a higher prevalence in women and older people, but it was also related to daily activities such as eye strain from computer use.
Astronauts were particularly afflicted, with about 30% of them experiencing symptoms during long-term space missions.
Dr March said the zero-gravity environment and the dry, enclosed cabin atmosphere, contributed to the development of DED in space.
Several factors were likely involved in the occurrence of DED, including tear-film instability and ocular surface inflammation in microgravity.
The tear film is challenged to remain stable and evenly spread due to altered fluid dynamics.
He said the space environment also exposed the eyes to floating dust, artificial lighting and prolonged screen use, which presented further risk of damage to the ocular surface.
Fluid shifts within zero gravity caused eyelid swelling and disrupted tear drainage, likely leading to tear retention and the build-up of irritants within the eye.
"Understanding DED in space will help protect astronauts' eye health, but also offer insights into the mechanisms of DED on Earth, and could lead to the development of innovative diagnostic and therapeutic solutions for it," he said.
These could include diagnostic technologies such as infrared imaging to provide non-invasive, portable methods to assess the tear film in real-time, while therapeutic devices such as ocular neurostimulators could stimulate tear production and alleviate DED symptoms at the push of a button.
"These advancements have significant implications for improving eyecare on Earth, particularly in remote or resource-limited settings such as rural areas, as well as in space."
The study team was made up of engineers, medical doctors, researchers from Western Sydney University and the University of Auckland, in collaboration with the German Aerospace Center (DLR).
Dr March said more research was planned, focusing on other eye conditions in a bid to contribute to the overall improvement of ocular health in space and on Earth.
