Long-term space missions may jeopardize astronauts' eyesight, warns study
That's what Université de Montréal opthalmology Santiago Costantino found in a study published last fall in the Journal of Engineering in Medicine and Biology.
At least 70 per cent of astronauts on the ISS have been affected by spaceflight-associated neuro-ocular syndrome, or SANS.
The researchers analyzed data from 13 astronauts, aged 48 on average, who spent 157 to 186 days on the ISS. The group included astronauts from the US, Europe, Japan, and Canada; 31% were women, and eight were on their first mission.
During the research, ophthalmologist Santiago Costantino from the Universite de Montreal discovered that over 70% of astronauts on the ISS experience spaceflight-associated neuro-ocular syndrome (SANS).
To study the effects of space travel, the researchers analyzed three eye-related factors: ocular rigidity, intraocular pressure, and ocular pulse amplitude. They measured ocular rigidity using optical coherence tomography with a customized video module to enhance choroid imaging, while tonometry was used to assess intraocular pressure and ocular pulse amplitude.
Significant changes were observed in the biomechanical properties of astronauts' eyes, with a 33% decline in ocular rigidity, an 11% drop in intraocular pressure, and a 25% decrease in ocular pulse amplitude. These alterations were associated with symptoms like reduced eye size, changes in focal field, and, in some cases, optic nerve swelling and retinal folds.
The researchers also found that five astronauts had a choroidal thickness greater than 400 micrometers, with no correlation to age, gender, or prior space experience. They suggest that weightlessness alters blood distribution in the body, increasing blood flow to the head and slowing venous circulation in the eye, which likely causes the choroid, the vascular layer nourishing the retina, to expand.
The researchers suggest that the choroid's expansion in weightlessness may stretch the collagen in the sclera, causing lasting changes to the eye's mechanical properties. Results have also shown that blood pulsations in microgravity could create a water-hammer effect, where sudden pressure changes in blood flow cause mechanical shock to the eye, leading to significant tissue changes.
The researchers found that these eye changes are typically not a major concern for missions lasting six to twelve months. While 80% of astronauts experienced at least one symptom, their eyes returned to normal after returning to Earth. In most cases, corrective eyeglasses were enough to address the symptoms developed aboard the ISS.
Space agencies and the research community remain cautious about the potential risks of longer missions, such as a Mars trip. The effects of prolonged microgravity exposure on eye health are still unclear, and no preventive or treatment measures are currently available.
Costantino and his team are waiting for more NASA data to further their research, and as the scientist pointed out, the changes in the eye's mechanical properties could help predict the development of spaceflight-associated neuro-ocular syndrome.
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