Space | 15. December 2021 | posted by Jan Oliver Löfken

SANS-CM bed rest study: Detecting space eye disease while lying down

Messung der Veränderung der Augachsenlänge mittels objektive Refraktion zum Ausschluss einer Verkürzung des Augapfels
Credit: © DLR. All rights reserved
A large number of eye examinations await the test persons in the current bed rest study. The image shows the measurement of the change in eye axis length by means of the so-called objective refraction to exclude a shortening of the eyeball.

Living in space puts an enormous strain on the body. Among other things, astronauts are exposed to space radiation and experience their muscles deteriorate and body fluids shift towards the head. To protect against the radiation, international research is being conducted on protective vests, for example in the MARE mission. Effective training programmes have been developed to combat muscle atrophy, so that today astronauts hardly have any difficulties upon returning to Earth, even after spending months on the International Space Station (ISS). However, the increased pressure in the head due to the changed fluid distribution can lead to permanent problems – especially for the eyes. Time and again, space travellers report a deterioration of their eyesight, with about 70 percent experiencing eye changes, either temporarily during the stay in space or permanently.

The causes are still unclear. There are some theories but no evidence explaining why this affects some astronauts and not others, but it is clear that the eye condition is a significant risk. If we think about the future of human spaceflight with missions to the Moon and Mars, stays in weightlessness will last longer and longer. Through all of this, the health and safety of the space travellers must be maintained. Therefore, reliable prevention and countermeasures are needed.##markend##

Bed rest studies have been used for many years to better understand the changes in the eye under increased pressure conditions such as in microgravity. In the current NASA and DLR study SANS-CM, our Institute of Aerospace Medicine is conducting extensive examinations during the bed-rest phases.

Credit: ©  DLR. All rights reserved
The measurement of the intraocular pressure by means of pneumatonometry is carried out while the patient is lying down and also in the countermeasure 'sitting'
Credit: ©  DLR. All rights reserved
Examination of the retinal reaction by electroretinogram (ERG) in the supine position

The scientific-medical focus: the eye

Among other things, the intraocular pressure is measured regularly, the retina and the optic nerve are examined, and the brain is monitored using an MRI. With optical coherence tomography, NASA has developed a method with which changes in the brain can be located with micrometre precision. The cardiovascular system is also under constant observation.

A twelve-member DLR team is on duty for all the examinations and experiments. Our study participants are often quite surprised at all the things we are investigating in detail on the subject of the eye. They are very interested and motivated to support us in our work - and thus help future astronauts.

Credit: ©  DLR. All rights reserved
Optical coherence tomography in the supine position examines the changes in the optic nerve head and retina

The proportion of 'earthly space travellers' in whom changes in the eye are detected in the current as well as past bed rest studies is similar as in the real space travellers. The optic nerve head swells somewhat and the ability to see at close range deteriorates slightly. The changes are reversible in participants of the bed rest studies. A little while after the end of the study, their eyes have completely regenerated. However, this can be different for people in space. There are former astronauts who have needed to wear glasses permanently after their return to Earth.

In search of countermeasures

During the VaPER bed rest study in 2017, the swelling of the optic nerve head was detected for the first time in some participants. The subjects lay in a six-degree head-down position for 30 days, the first time without a pillow.

The follow-up study AGBRESA 2019 also detected the change in the optic nerve head. We tested a possible countermeasure with rides on the DLR short-arm centrifuge. With the current bed rest study SANS-CM, which will enter the next round in early 2022, we are again testing countermeasures on behalf of NASA. One is the negative pressure chamber LBNP (Lower Body Negative Pressure Device). In later campaigns, for example, cycling training will be used.

Glaucoma, a well-known disease in space and on Earth

SANS stands for Spaceflight Associated Neuro-ocular Syndrome, an eye condition that often affects astronauts during long stays in weightlessness. It includes problems from which earthly patients also suffer, such as changes in intraocular pressure. Glaucoma is a well-known condition that includes various pathological changes in the eye resulting from increased intraocular pressure. It is a widespread disease and one of the most common causes of blindness.

SANS, or glaucoma, occurs in space due to the lack of gravity, but also on Earth, for example, when people lie down for long periods of time. Since glaucoma is not always noticed early on by those affected and can lead to irreversible blindness, a better understanding of how the disease develops and progresses as well as the development of suitable countermeasures are particularly important  - for people in space and on Earth.

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How does microgravity affect the human body? And how can we counteract the negative effects? On Earth, bed rest studies are used to study the effects of microgravity on the human body in order to investigate reactions, effects and countermeasures. to authorpage