Ophthalmology in Space: Mars Mission in Sight?

A far cry from the first spaceflight undergone by the USSR in 1961, which took a total of 108 minutes to orbit Earth, today’s space missions can last for hundreds of days at a time. In 2017, Peggy Whitson set the NASA record for the most cumulative days living and working in space at 665 days. For a single mission aboard the International Space Station (ISS), NASA astronaut Scott Kelly holds the record at 340 days. He, and seven other astronauts, have spent more than 200 days in space during a single spaceflight.

Within two weeks after being on the ISS, some astronauts were noticing blurred vision

Although these achievements are impressive, as the longevity of space missions increase, so too do concerns about the health of those aboard the ISS. Ocular complications, for example, are often experienced while in spaceflight and after returning from the station.

Referred to as Space-Associated Neuro- Ocular Syndrome (SANS), astronauts involved in longer duration spaceflight are presenting with unusual physiologic and pathologic neuro-ophthalmic findings associated with prolonged exposure to microgravity – where gravity in space is weaker than that on Earth. The signs of SANS manifest as increased swelling in the blood supply layers (the choroid) behind the retina, swelling of the optic nerve as it enters the eye, and refractive error change.

“Within two weeks after being on the ISS, some astronauts were noticing blurred vision. NASA confirmed that the astronauts were more hyperopic when they returned to Earth,” said Steve Thomas, Clinical Market Development Manager for Heidelberg Engineering in the U.S.

During their meeting at the AAO in 2012, NASA told Mr Thomas that these complaints had been presenting from as early as the Apollo Missions in the 1960s and the Space Shuttle Missions beginning in 1981. While the negative effects of microgravity on bone growth and muscular development had long been known, the state of ocular health was now on NASA’s radar too.

“Aboard the ISS, missions can actually be up to six months in length and that’s when NASA really started to understand that they had recurrent manifestations on different crew members. As a result, they wanted a way to solve this problem.”

NASA’s ability to study vision changes in relatively short duration flights has proven crucial to the viability of a Mars mission, which could be as long as three or more years. While there is evidence of ocular issues associated with the average mission length of six months, getting to and from Mars is predicted to take up to 20 months in itself.

The planned Mars trip also involves astronauts encountering three different gravity fields. When in microgravity, the fluids in the body shift upward to the head, causing pressure on the eyes that can result in vision problems. In other words, the longer the duration, and the more complex the gravity changes, the more challenging the potential ocular issues become.

In addition, Mr Thomas comments that, upon the presentation of ocular issues in returning astronauts, “The eye has become high on NASA’s list of trying to get a resolution or some kind of mitigation techniques so that Mars missions can proceed in a way that would be beneficial and safe for everyone.”

HEIDELBERG’S SOLUTION

Heidelberg Engineering could help to solve NASA’s problem. Researching the effects of microgravity on vision would require a range of diagnostic tools including fundus photography, visual fields, cardiac blood flow and echography – and optical coherence tomography (OCT) – a task they bestowed upon their ophthalmic imaging platform, the Spectralis.

Compared to other devices, Heidelberg Engineering says the Spectralis had an extremely small form factor, was light weight, had high imaging capability, more imaging modes, and was the only system of its kind with a sophisticated tracking mechanism which, Mr Thomas explains, “enabled a very, very high degree of reproducibility that actually put us well above the competition for being able to monitor and diagnose extremely small shifts in any changes in the ocular health of the crew members”.

In an average mission of six crew members, they must all image each other’s eyes on a fortnightly basis to obtain the vital information required by NASA

In 2013, clearance was given to launch the Spectralis into space with the aim to study the effects of microgravity on posterior ocular structures.

“We did extensive testing regarding the device’s suitability for use in microgravity, but, in the end, it was effectively a regular device that was sent to the ISS,” said Dr Tilman Otto, Head of Technology Management Ophthalmic Devices at Heidelberg Engineering.

“On 5 June 2013, we organised a small party on the occasion of the launch of the Spectralis and watched, together with Gerhard, the live transmission of the launch of the Albert Einstein Automated Transfer Vehicle (ATV) on an Ariane 5 rocket from Kourou, French Guiana.”

The late Gerhard Zinser, PhD, Heidelberg Engineering Co-Founder – remembered as a pioneer, inventor and driving force behind many of Heidelberg Engineering’s groundbreaking technologies and products – played a particularly personal role in the project and collaboration with NASA. His lifelong passion for astronomy began as a child and developed into his physics degree, where he attended lectures in astrophysics and studied astronomy journals.

“Already as a 10-year-old boy, Gerhard observed the planets and stars with a small telescope that his grandmother had given to him. In his youth, he made black and white photographs of solar spots, protuberances and lunar craters, and developed the films and pictures himself,” Dr Otto told mivision.

“His interest in space travel was awakened by the first moon landing in 1969, which he followed very closely at the age of 15.

“The project to send a Spectralis OCT to the International Space Station was a top priority for Gerhard and he enthusiastically followed the progress of the project.”

It was later in 2013 that Dr Otto recalls Dr Zinser proudly announcing that the Spectralis had safely reached the ISS and the first images had been taken.

Using OCT, a non-invasive imaging test that uses light waves to take a high resolution cross-sectional picture of the retina, choroid and optic nerve head, the Spectralis quickly became a primary diagnostic tool for the early detection and monitoring of SANS.¹ 

it’s very rare for somebody to come back and have absolutely no effect from a mission…

ASTRONAUT TO OPHTHALMOLOGIST

While, for an optometrist or ophthalmologist, working with an OCT device in clinical practice is not anything out-of-this-world, when aboard the ISS, and in the hands of an astronaut, it is exactly that.

To put it into perspective, imagine you have a device like the Spectralis and you place it in the hands of somebody who has no prior knowledge of ophthalmic examination and say to them, “You need to operate this in order to get a certain kind of information from person A”.

Tricky, right?

Now imagine that there is a minor delay in the communication between these people. And, to further complicate things, it might have been months since person A last had any experience with such a device.

Well, that was, and continues to be, the reality of the astronauts working with the Spectralis on the ISS. In an average mission of six crew members, they must all image each other’s eyes on a fortnightly basis to obtain the vital information required by NASA.

While Mr Thomas says some of the astronauts are “naturally talented with any kind of technical device… and just seem to zip through the imaging session as if they were born into the device,” what really makes everything operate smoothly is the group of people, back on Earth, responsible for watching, through a live link, everything the astronauts are doing externally, and then communicating instructions remotely.

These people make up the ground guidance team and their role is to communicate from Mission Control to the ISS to ensure the crew are taking and receiving optimal information while performing OCT.

“They basically guide the astronaut as to what to do next, giving instructions such as, ‘this is how to move the device, this is how to capture the image, this is how to do this and that’,” says Mr Thomas. “Because they can see everything happening on the software, the crew members are usually able to get through a session.”

SECOND SPECTRALIS FOR THE ISS

With the ability to image the deeper layers of the choroid and optic nerve, in 2018 NASA launched a new and improved Spectralis with OCT2 Module to work alongside the original Spectralis on board the ISS. With the OCT2 Module, acquisition time of Bruch’s membrane opening, minimum rim width, and retinal nerve fibre layer scans is now less than half of the acquisition time of the previous Spectralis OCT.²  This next-generation also has the ability to capture more complex scans while considering the use of additional modalities.³ 

A study to compare the two models found that OCT2 technology can improve diagnostic imaging in glaucoma and that the reduced acquisition time makes the imaging process easier for both the patient and the examiner.² This improves clinical workflow and increases patient comfort by shortening examination times – perfect for the far from ordinary situation aboard the ISS.

BACK DOWN TO EARTH

On their return to Earth, astronauts go through a full clinical debrief – a conclusion to the initial pre-flight clinical work-up and fortnightly monitoring on the ISS. Over the years, Mr Thomas has been able to meet different crew members involved in the research. For some, he did their primary imaging before their missions and then, once they returned to Earth, visited them again to observe their changes.

Mr Thomas noted that while some of the SANS ocular findings fade, others do not.

“Everyone has been a little different, but I think it’s safe to say that within six months, a lot of crew members have returned to normal. There’s only been a really small number of cases where findings are significant enough to impact their visual health as a permanent situation.

“So that’s the good news, but again, we’re only talking about relatively short duration missions compared to what’s coming. The thinking is that on longer missions, not only would the ocular changes really interfere with their ability to complete their mission, but perhaps the probability of these findings becoming more permanent is higher.”

The findings so far have indicated that there is a possible genetic link to who’s susceptible to SANS and who’s not. As well as this, Mr Thomas says there appears to be more tolerance with females versus males, with older male crew members in a higher risk group.

Though not all findings are conclusive. While it is believed that diet and vitamin B12 play a role in protecting long-term eye health, the findings relative to this are only new and more research and time is required to understand them as genetic markers.

One thing is for sure, “it’s very rare for somebody to come back and have absolutely no effect from a mission, at least on ocular findings,” said Mr Thomas.

While there is still a way to go, the goal of a Mars mission is slowly coming within reach.

References 

1. Lee, A.G., Mader, T.H., Gibson, C.R. et al. Spaceflight associated neuro-ocular syndrome (SANS) and the neuroophthalmologic effects of microgravity: a review and an update. npj Microgravity 6, 7 (2020). doi.org/10.1038/ s41526-020-0097-9 
2. Bosche F, Andresen J, Li D, Holz F, Brinkmann C. Spectralis OCT1 versus OCT2: Time Efficiency and Image Quality of Retinal Nerve Fiber Layer Thickness and Bruch’s Membrane Opening Analysis for Glaucoma Patients. J Curr Glaucoma Pract. 2019;13(1):16-20. doi:10.5005/jpjournals- 10078-1244 
3. eyewire.news/articles/heidelberg-engineerings-spectralisoct2- module-headed-to-the-international-space-station