Abstract
Purpose :
Spaceflight associated neuro-ocular syndrome (SANS) is common amongst astronauts on long duration space missions and is associated with signs consistent with elevated cerebrospinal fluid (CSF) pressure. Additionally, CSF pressure has been found to be elevated in a significant proportion of astronauts in whom lumbar puncture was performed after successful mission completion.
Methods :
We have developed a retinal photoplethysmographic technique to measure retinal vein pulsation amplitudes. This technique objectively measures retinal vein pulse amplitudes at mulitple locations across a range of intraocular pressures (IOP). From this we can calculate the IOP and CSF pressure balance point and knowing the IOP, predict CSF pressure. We measured the pulse amplitudes in 14 eyes of 7 healthy volunteers in the sitting and supine posture to mimic the range of tilt table extremes and estimated the induced CSF pressure change using measurements from the CSF hydrostatic indifferent point. We then correlated the pulse amplitude changes to estimated change in CSF pressure.
Results :
We found a significant relationship between pulsation amplitude change and estimated CSF pressure change (p < 0.0001) across a range from 2.7 to 7.1mmHg. The increase in pulse amplitude was highest in the sitting posture with greater estimated CSF pressure increase (p < 0.0001), in keeping with physiologically predicted CSF pressure response. In all eyes where stimated CSF pressure change was greater than 3.9mmHg, we could detect a significant change in retinal vein pulse amplitude.
Conclusions :
This technique may be useful for non-invasive measurement of CSF pressure fluctuations within individuals during long-term space voyages. It appears to be able to detect a CSF pressure change of 4 or more mmHg.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.