The Eye Movements and Motion Perception Induced By Off-Axis Rotation at Small Angles of Tilt After Spaceflight (OVAR) study allows for better understanding of normal balance and suggest causes for abnormal balance after space flight.Principal Investigator(s)
French National Center for Scientific Research (CNRS), Toulouse, , France
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)Research Benefits
Information PendingISS Expedition Duration:
October 2004 - October 2005Expeditions Assigned
10,11Previous ISS Missions
As a DSO, OVAR was performed on crewmembers during ISS Increments 10 and 11.
The Eye Movements and Motion Perception Induced By Off-Axis Rotation at Small Angles of Tilt After Spaceflight (OVAR) is a Detailed Supplementary Objective (DSO). A DSO is a medical investigation supplementary to the primary investigation performed voluntarily by the crewmembers. DSOs are designed to require minimal crew time, power and stowage; and are focused on studying adaptation to microgravity.
The objective of OVAR is to assess the changes in otolith (small particles found in the inner ear which aid in balance) information processing following adaptation to microgravity by comparing eye movements and the process of the brain by which we understand and interpret the information we receive through the eyes before and after space flight.
The inner ear contains two balance-sensing organs; the semicircular canals (fluid-filled tubes located inside of the ear that control balance) which sense rotation, and the otoliths which sense both translation and position of the head relative to gravity. During rotation at a constant velocity (speed of an object in a certain direction) about an axis (the center around which something rotates) tilted relative to gravity, only the otolith organs are stimulated by the change in head position relative to gravity. Movements of the eye during OVAR will accurately reflect processing of the otolith signals by the brain.
This study will allow for better understanding of normal balance and suggest causes for abnormal balance related to microgravity exposure. In particular, space flight will provide knowledge and understanding of the vestibular system (sensory system that contributes to balance and sense of orientation), which is one of the systems most affected by gravity.Earth Applications
This study will allow for better understanding of normal balance and suggest causes for abnormal balance in patients on Earth. If OVAR, associated with a 3-D eye movement measuring system, proves that reliable information about otolith organs can be obtained, then this test has obvious clinical value to assess vestibular disorders.
OVAR has no inflight requirements.Operational Protocols
Eye movements and motion perception will be recorded during OVAR clockwise and counterclockwise at various angles and speeds. Three preflight sessions will occur at three, two, and one month before launch; followed by five sessions postflight on landing day, R+1, R+2, R+4, and R+8 days.
Ocular counter-rolling (OCR) is an orienting eye movement that is generated during head roll tilt and mediated by a part of the bony inner ear called the otolith organ. The OCR reflex (presumably activated by tilt relative to gravity to maintain the vertical axis of the eye aligned with the visual environment) and the sense of roll tilt were evaluated in seven astronauts before and after 10?13 day space missions on board the Space Shuttle. Off-vertical axis rotation (OVAR) at 1/8 revolution per second in darkness at 10-degree and 20-degrees angles of tilt were done in 3 preflight and 3 postflight sessions 2?24 hours, two, and four days after landing.
OVAR has the advantage of generating cyclic testing control of OCR, allowing averaged measurements over several cycles, presumably improving measurement accuracy over static head tilt tests. Results show there was no significant difference in OCR during OVAR immediately after landing compared to preflight. However, the perceived degree of the roll tilt during OVAR was significantly larger immediately postflight, and then returned to control values in the following days. Since the OCR response is mainly due to the shearing force exerted on the otoliths by tilt relative to gravity, the absence of change in OCR postflight suggests that the peripheral otolith organs function normally after short-term space flight. However, the increased sense of roll tilt indicates an adaptation in the central neural processing of gravitational input, supposedly related to a re-weighting of the internal model of gravity, or lack thereof, as an adaptation to microgravity.
These results suggest a separation between otolith-driven eye movement and orientation perception during passive vestibular stimulation by inertial motion after space flight, and support the conclusion that otolith-driven compensatory eye movement and orientation perception are controlled by different neural mechanisms. OCR is primarily a direct response of otolith activation by low-frequency linear acceleration along the axis between the ears, whereas perception of tilt is primarily governed by the integration of otolith inputs, as well as bodily sensations such as position of limbs and pressure on the skin and internal organs. Apparently, the peripheral vestibular organ showed little or no changes after 10-13 days space flight, thus otolith-driven eye movements appear relatively unaffected by short-term exposure to microgravity. However, the central processing of orientation relative to gravity is likely to be affected and suggests why perceptual and oculomotor responses dependent on central vestibular processing can be greatly disrupted (Clement et al. 2007).
Clement G, Denise P, Reschke MF, Wood SJ. Human ocular counter-rolling and roll tilt perception during off-vertical axis rotation after spaceflight. Journal of Vestibular Research. 2007; 17(5-6): 209-215. PMID: 18626132.