July 2019
Volume 60, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2019
Contribution of intraocular pressure disparity in head-down tilt to the development of Spaceflight-Associated Neuro-ocular Syndrome
Author Affiliations & Notes
  • Nitya Murthy
    Kentucky College of Optometry, University of Pikeville, Pikeville, Kentucky, United States
  • Mark Wayne Mutter
    Kentucky College of Optometry, University of Pikeville, Pikeville, Kentucky, United States
  • John Bradley
    Kentucky College of Optometry, University of Pikeville, Pikeville, Kentucky, United States
  • Lewis Josh Watson
    Kentucky College of Osteopathic Medicine, University of Pikeville, Pikeville, Kentucky, United States
    Kentucky College of Optometry, University of Pikeville, Pikeville, Kentucky, United States
  • Adam Hickenbotham
    College of Health Sciences, Tusculum University, Tusculum, Tennessee, United States
    Kentucky College of Optometry, University of Pikeville, Pikeville, Kentucky, United States
  • Eilene Kinzer
    Kentucky College of Optometry, University of Pikeville, Pikeville, Kentucky, United States
  • Footnotes
    Commercial Relationships   Nitya Murthy, None; Mark Mutter, None; John Bradley, None; Lewis Watson, None; Adam Hickenbotham, None; Eilene Kinzer, None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science July 2019, Vol.60, 2260. doi:
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      Nitya Murthy, Mark Wayne Mutter, John Bradley, Lewis Josh Watson, Adam Hickenbotham, Eilene Kinzer; Contribution of intraocular pressure disparity in head-down tilt to the development of Spaceflight-Associated Neuro-ocular Syndrome. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2260.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Spaceflight-Associated Neuro-ocular Syndrome (SANS), a pathology occurring in astronauts during and after long-duration spaceflight, features more severe disc edema in the right eye. Head-down tilt (HDT) is commonly used as a ground-based analog to simulate cephalad fluid shifts in microgravity. Intraocular pressure (IOP) rises in positions of HDT and contributes to optic disc edema. We tested the hypothesis that IOP is more elevated in the right eye (OD) than the left eye (OS) during head-down tilt.

Methods : Subjects were healthy adults (n=30, 19 females, 11 males, mean age=24.2±2.2 years). Subjects' IOP was measured every minute for five minutes at supine, 15°, 30° and 45° of HDT. An electroretinogram (ERG) was performed every five minutes in each eye. Implicit times (ms) and amplitudes (μV) were measured in both eyes after 5 minutes of 15°, 30° and 45° head tilt.

Results : After 5 minutes of 0°, 15°, 30° and 45° of HDT, mean IOP in the right eye was 15.9±0.9, 19.2±1.0, 23.1±1.3 and 27.8±1.3 mmHg and mean IOP in the left eye was 14.9±0.9, 15.8±1.0, 19.5±1.1, 22.4±0.8 mmHg. IOP was increased after 5 minutes of 30° and 45° HDT in both eyes (p<0.03 in all conditions). IOP increased more OD than OS after 5 minutes of 45° HDT (p<0.03). 5 minutes of 45° HDT caused an increase in implicit time at 16 td/s in OD that was not seen in OS (p<0.03). Amplitude was significantly reduced at 4 td/s (14.1±5.3 vs. 10.9± 3.0 μV, p<0.03) and 16 td/s (21.4±8.6 vs 16.6±5.6 μV, p<0.03) after 5 min of 45° compared to 15°. This reduction was not seen OS (p=0.05).

Conclusions : IOP increased OD relative to OS during HDT with a 19% increase at 45° HDT, while no differences were seen at the supine position. Amplitude was more greatly reduced OD. We propose that the disparity in IOP between the OD and OS seen in HDT is due to internal jugular vein (IJV) drainage. It is well-known that jugular venous distension increases in HDT as well as in microgravity. Studies show that the majority of people have an anatomic tendency to have higher outflow in the right IJV. We propose that the increased outflow through the right IJV contributes to increased IOP, thereby leading to increased optic disc edema OD. These results have significant impact on the theory and understanding of the etiology of SANS.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Figure 1: * is p<0.05 OD sup vs OD 45°, # is p<0.05 OS sup vs OS 45°, & is p<0.05 OD 45° vs OS 45°.

Figure 1: * is p<0.05 OD sup vs OD 45°, # is p<0.05 OS sup vs OS 45°, & is p<0.05 OD 45° vs OS 45°.

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