Purpose:

To investigate the effect of spaceflight on human eyeballs (particularly during ascent, not microgravity). This seeks to provide more insight into what could be the cause of Spaceflight Associated Neuro-Ocular Syndrome (SANS)- a visual-impairment condition experienced by approximately 70% of astronauts which still has an unknown cause.


Existing Research:

  • Very little research on ascent – hence why this is interesting!
  • Expected that this is determined by elastic properties of the optic nerve (and maybe eye) which would be affected if the eyeballs are squished launch and landing – https://pure.rug.nl/ws/portalfiles/portal/133399769/1_s2.0_S0142961219308397_main.pdf
  • Closest we get is this: (Tl; dr: they started measuring 21 minutes after weightlessness still on flight but not during the initial time period of launch itself)


In 1994 a Russian publication provided evidence of ICP measurements during shortduration spaceflight in a Macaque monkey named Krosh on the biosatellite Cosmos-2229 (Krotov et al. 1994). A surgically implanted pressure sensor was placed in contact with the dura mater 25-30 days before launch. ICP was measured during seven 5-minute sessions throughout the 20 hours before launch, continuously for 2 hours starting 21 minutes after entering weightlessness, and then for 5 minutes every 2 hours throughout the duration of the flight. Before launch, while in the rocket on the launch pad, ICP in the “physical mid-position” (head and legs at the same level) averaged 10.23 ± 0.12 mmHg (range: 8.5 – 12.1 mmHg). During the final 2 hours before flight the average ICP was 11.66 ± 0.09 mmHg. Twenty-two minutes after entering weightlessness ICP was 13.78 mmHg and continued to increase to ~15 mmHg over the first few hours. By flight days 3 to 5 ICP reached an average of 14 mmHg, driven in large part by increased ICP during the night. Conversely, from flight days 6 to 9 ICP was higher during the day than at night and the average ICP returned to values that were similar to preflight baseline. Disruption in the sleep-wake cycle throughout the mission led to the changes in the circadian pressure rhythm such that ICP was higher at night than during the day on flight day 8 and 9. The ICP pulse also demonstrated changes during weightlessness, with a decrease in amplitude of the arterial component and an increase in amplitude of the venous component. This also tended to return toward preflight morphology during flight days 5 to 9. In comparison to the 4 mmHg change in ICP observed from preflight to weightlessness, posture changes on Earth (moving the monkey from upright to supine) increased ICP by 10 mmHg.

Source: https://humanresearchroadmap.nasa.gov/Evidence/reports/SANS.pdf


Potentially Related Phenomenon:

  • hyperopia: eye condition in which deformations in anatomical geometry of the eye result in farsightedness

Velez, G., Tsang, S. H., Tsai, Y.-T., Hsu, C.-W., Gore, A., Abdelhakim, A. H., Mahajan, M., Silverman, R. H., Sparrow, J. R., Bassuk, A. G., & Mahajan, V. B. (2017). Gene therapy restores Mfrp and corrects axial eye length. Scientific Reports, 7(1). https://doi.org/10.1038/s41598-017-16275-8


Our Research Objective:

To measure eye deformation experienced during ascent to inform whether or not changes in eye elasticity could be a cause of SANS.


An overview of how we intended to conduct this research:

  • place eyeballs within the payload of our rocket and collect images of them during ascent
  • analyze these images for any deformations in the eye


Experimental specifics:

  • Raspberry Pi cameras would be used to collect images of the eyes
  • LEDs would be placed inside the pressure vessel so that there would be enough light to capture images of the eyes
  • cow eyeballs would be used (since applying this experiment to human eyeballs would be invasive) and would be oriented facing upward (similar to how astronauts face upward during rocket launches)
  • three eyeballs would be used to provide more data (preferably more eyeballs, but limited to three due to other design constraints)
  • the eyes would be secured within a pressure vessel (to prevent other factors from deforming the eyeballs)
  • vibration damping materials would surround the pressure vessel, to ensure the eyes remain secured


Unanswered research problems:

  • How do we ensure the eyeballs remained preserved while they are in the rocket? (especially since launch is in New Mexico during the summer)
    • proposed potentially using ice packs to surround the eyeballs (likely outside of the pressure vessel)
  • Will our current measures be enough to ensure the eyeballs do not move around during launch?
  • How can we recover the images after launch?
  • How can we measure and how do we quantify our results? Will the image quality of the recovered data be sufficient to depict any notable changes in eye shape?


Research Proposal Submitted to Spaceport


Cyclops: A Biomechanical Characterization of Hypergravity-Induced Globe Flattening of B. taurus for Evaluation of Spaceflight Launch and Landing Contributions to Spaceflight Associated Neuro-Ocular Syndrome (SANS)

Spaceflight Associated Neuro-Ocular Syndrome (SANS) is a collection of impairments to astronaut visual acuity associated with spaceflight and characterized by long-term altered neuro-ocular structure and function (Lee et al., 2020). SANS has been identified by the NASA Human System and Risk Board as a mitigation priority for future manned deep-space journeys, as presently up to 75% of all astronauts experience reduced visual acuity including persistent ocular structural changes several years following long-duration spaceflight (Stenger et al., 2017; Yang et al., 2022; Lee et al., 2020).

The precise etiology of SANS is currently unclear, although extended measurement of visual acuity is presently incorporated in routine International Space Station (ISS) biometric monitoring and has been studied since the Mercury program (Lee et al., 2020; Duntley et al., 1966). ISS biometric monitoring has identified a number of conditions characterizing SANS including bilateral optic disc edema, globe flattening, choroidal and retinal folds, and hyperopic refractive error shifts (Lee et al., 2020). These observed visual acuities present two leading proposed etiologies of SANS—elevated intracranial pressure (ICP) from cephalad fluid shifts and compartmentalization of cerebrospinal fluid (CSF) within the orbital optic nerve sheath (Lee et al., 2020).

While ICP is generally the preferred mechanistic hypothesis for SANS, several factors challenge the ICP hypothesis. Most notably, terrestrial ICP is usually caused by idiopathic intracranial hypertension (IIH) resulting in similar physiological manifestations as SANS including optic disc edema, globe flattening, choroidal folds, or hyperopic shifts. However, despite 90% of IIH patients presenting chronic severe headaches, 68% of IIH patients presenting transient visual obscurations, and 30% of IIH patients presenting diplopia, no astronaut with identified SANS symptoms of optic disc edema, globe flattening, choroidal folds or hyperopic shifts presented with chronic severe headaches, transient visual obscurations or diplopia (Lee et al., 2020). Other discrepancies between SANS and IIH including asymmetric disc edema challenge the ICP hypothesis, introducing the possibility of additional etiological contributions from other sources of ICP outside of cephalad fluid shifts (Lee et al., 2020).

One major understudied element of spaceflight effects on visual acuity is the hypergravity environment of launch. ISS biometric monitoring including high-resolution 3-Tesla magnetic strength MR imaging of head and orbits are only collected “prior to and as soon as possible after spaceflight” (Lee et al., 2020). Several functional barriers prevent in-vivo investigation of ocular performance during launch including lack of instruments aboard launch vehicles to perform necessary biomedical monitoring such as Amsler grid, ophthalmoscopy, tonometry, fundus photography, orbital ultrasound and OCT—all available on the ISS (Lee et al., 2020). Additionally, the necessity for astronauts to remain restrained to their seats for launch safety and perform vehicle-related activity during launch limit the scope of visual acuity monitoring that may be performed during launch.

To address this gap in spaceflight hypergravity effects on visual acuity, Cyclops is a proposed sounding rocket payload experiment investigating of the biomechanical effects of hypergravity on the SANS symptom of hyperopic globe flattening of an in-vitro B. taurus ocular specimen. Cyclops will specifically test the hypothesis that launch and landing conditions contribute significant gravity-induced ocular pressure in addition to ICP by observing whether the amount of globe flattening observed during a sounding rocket flight is on the order of overall globe flattening levels measured in SANS-affected astronauts.

Globe flattening shall specifically be characterized through repeated in-flight axial imaging of the specimen to produce a relationship between axial length change and hypergravity pressure (Sibony et al., 2023). An example of an ultrasound globe flattening observation is provided in Figure 1., though an in-vitro sample will allow for traditional optical imaging to measurement of globe flattening without need for ultrasound.


Figure 1. Schematic of hyperopic globe flattening to be measured with Cyclops. Adapted from
Velez et al., 2017.

The payload is designed to be approximately 10 lbs. and stored within in a standard 3U Cubesat dispenser (contained completely within dims ions of 10x10x30 cm). The payload is additionally designed to be able to integrate modularly with the rest of the vehicle, with minimal interference with launch operations.

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