Qualitative analysis of the presence of gaze-evoked nystagmus in astronauts after long term space flights. Results of “field test” experiment

• Published in: Acta astronautica 2024-11, Vol.224, p.82-88
• Main Authors: Tomilovskaya, Elena, Bekreneva, Maria, Rukavishnikov, Ilya, Kofman, Igor, Kitov, Vladimir, Lysova, Nataliya, Rosenberg, Marissa, Grishin, Alexey, Saveko, Alina, Fomina, Elena, Wood, Scott J., Reschke, Millard
• Format: Article
• Language: English
• Subjects: Field test; Functional performance; Nystagmus; Sensorimotor system; Space flight; Vestibular apparatus; Weightlessness
• ISSN: 0094-5765
• DOI: 10.1016/j.actaastro.2024.07.026

In the first days after a spaceflight (SF), re-entry motion sickness and motor coordination problems reflect the need to readapt back to the natural gravitational state. Gravity is a natural stimulus for the receptors of vestibular apparatus, which plays an important role in multisensory interactions. Changes indicating an increase in excitability of the vestibular apparatus during SF (Kornilova et al., 2017) suggest a high probability of the occurrence of gaze-evoked nystagmus after prolonged SF. Russian-American experiment “Field Test” included a nystagmus test. 22 ISS crewmembers (14 Russian cosmonauts and 8 astronauts; flight duration 159.8 ± 19.5 days) participated in the experiment. The study was conducted twice before flight and several times after flight, starting within 3 h after landing. In a seated position, astronauts tracked with their eyes only (without moving their head) horizontal and vertical movements of the researcher's finger from the central position to the gaze end points (right, left, upper). Eye movements were recorded with a video camera. The videos were analyzed qualitatively for presence of nystagmus. Preflight, gaze-evoked nystagmus was detected in 5 people, the greatest changes were observed on landing day. 10 crewmembers exhibited nystagmus in the extreme left gaze position and 13 crewmembers – in the extreme right gaze position (partial recovery was observed 1–4 days after SF). A noticeable decrease in the frequency of manifestation of the nystagmus was observed only 10–13 days after landing (n = 16). Gaze-evoked nystagmus is usually considered a clinical sign of cerebellar alterations. However, it is often described in healthy people with a prevalence of up to 21 %. In a similar study involving 18 astronauts, participants of long-term SF, the frequency of occurrence of gaze-evoked nystagmus also increased in the first hours after SF (Reschke, Good and Clement, 2017). However, in this study, a detailed analysis of the presence of nystagmus in various directions was conducted for the first time. Of particular interest is the frequent detection of a gaze-evoked nystagmus in the right position after SF - this phenomenon may be a sign of presence of a central vestibular imbalance (Robinson et al., 1984), which also occurs in patients with cerebellar disorders (Bayer and Dietrich, 2011). The results allow us to expand our understanding of the severity and frequency of vestibular disorders and the dynamics of their recovery after p