To compare structural and functional ocular outcomes between14-and 70-day HDTBR in healthy human subjects

Cromwell, R. L.

Ploutz-Snyder, R. J.

Taibbi, G.

Vizzeri, G.

Yarbough, P. O.

Zanello, S. B.

NASA Technical Reports Server

BACKGROUND
METHODS
METHODS
• To compare structural and functional ocular outcomes between 14-
and 70-day HDTBR in healthy human subjects
Comparison of Structural and Functional Ocular 
Outcomes Between 14- and 70-day Bed Rest
R.L. Cromwell,1 G. Taibbi,2 S. B. Zanello,1 P.O. Yarbough,1 R.J. Ploutz-Snyder,1 and G. Vizzeri2
CONCLUSIONS
DISCLOSURE
All Authors, None
ronita.l.cromwell@nasa.gov
NASA bed rest studies STANDARDIZED CONDITIONS
 Subject to rest in bed at all times
 Monitoring by a subject monitor and an in room camera
24-hour a day
 Daily measurement of vital signs, body weight, fluid 
intake and fluid output
 No napping permitted between 6:00 am and 10:00 pm
 Standardized diet
1 Universities Space Research Association, Division of Space Life Sciences, Houston, TX 2 Department of Ophthalmology and Visual Sciences, The University of Texas Medical Branch, Galveston, TX
RESULTS
SUPPORT
NASA Flight Analogs Project, 516724.03.04.01
NIH/NCAT 1UL1RR029876-01
RESULTS
• NASA standard HDTBR screening procedures (healthy adults)
OCULAR EXAMS:
Pre-BR 
2 office visits 2 office visits
Post-BR 
2 office visits 1 office visit
HDTBR Duration70 days 14 days
• Two integrated, multidisciplinary studies conducted at NASA Flight
Analogs Research Unit (FARU): 14- and 70-day 6º HDTBR
PURPOSE
Source: nasa.gov
• Ophthalmological changes have been recently reported in some
astronauts involved in long-duration space missions:
• Elevated intracranial pressure resulting from µG-induced cephalad
fluid shifts may be responsible for most of these findings
From Mader et al. Ophthalmology 2011;118(10):2058-69
• There was a slight RNFL thickening post-HDTBR, without signs of
optic disc edema. Such changes may have resulted from HDTBR-
induced cephalad fluids shift.
• In both studies:
• Hypothesis: the amount of ocular changes induced by HDTBR is
affected by the time spent in the HDTBR position
During BR 
Weekly (FARU)Weekly (FARU)
• Head-down tilt bed rest (HDTBR) produces cephalad fluid shifts;
used to simulate the effects of µG on the human body
• Mixed-effects linear models compared pre- and post-HDTBR observations between
14- and 70-day HDTBR in:
• 70-day HDTBR induced greater peripapillary retinal thickening than
14-day HDTBR, suggesting that the time spent in the 6º HDTBR
position may affect the amount of optic disc swelling
14-day HDTBR
(n = 16)
70-day HDTBR
(n = 6)
Age 37.8 (8.8) 39.5 (7.8)
Gender (Male/Female) 12/4 5/1
Height, cm 174.9 (8.3) 171.3 (5.9)
Weight, Kg 76.4 (10.4) 76.2 (8.4)
Data presented as mean (sd). 
One subject participated in both bed rest campaigns
14-day HDTBR 70-day HDTBR
Pre Post Pre Post
Near BCVA, logMAR -0.12 (-0.15, -0.09) -0.17 (-0.20, -0.14) -0.16 (-0.21, -0.11) -0.19 (-0.24, -0.14)
Spherical Equivalent, D -0.25 (-0.87, 0.37) -0.45 (-1.07, 1.51) 0.77 (-0.25, 1.79) 0.49 (-0.53, 1.51)
Goldmann IOP, mmHg 15.17 (13.64, 16.70) 14.67 (13.14, 16.20) 15.42 (12.92, 17.91) 14.96 (12.41, 17.51)
iCare IOP, mmHg 13.78 (11.91, 15.66) 14.09 (12.21, 15.96) 13.21 (10.15, 16.27) 13.62 (10.52, 16.73)
Peripapillary retinal thickness
Temporal, μm 304.31 (293.06, 315.56) 307.41 (296.15, 318.66) 307.17 (288.79, 325.54) 311.83 (293.49, 330.17)
Superior, μm 386.91 (372.60, 401.21) 391.59 (377.29, 405.90) 407.25 (383.89, 430.61) 418.75 (395.46, 442.04)
Nasal, μm 356.38 (345.19, 367.56) 361.00 (349.82, 372.18) 351.67 (333.40, 369.93) 363.13 (345.00, 381.25)
Inferior, μm 397.03 (382.45, 411.61) 401.38 (386.79, 415.96) 400.92 (377.11, 424.73) 411.00 (387.25, 434.75)
Central, μm 306.67 (261.27, 352.07) 310.69 (265.30, 356.08) 299.60 (218.41, 380.79) 312.10 (231.02, 393.18)
Average RNFL thickness, μm 96.94 (92.56, 101.32) 98.09 (93.71, 102.48) 103.42 (96.26, 110.57) 105.13 (98.00, 112.26)
Macular thickness, μm 279.45 (270.22, 288.67) 276.97 (267.75, 286.19) 268.25 (253.19, 283.31) 266.63 (251.59, 281.66)
Data presented as mean (95% Confidence Interval).
BCVA, best corrected visual acuity; IOP, intraocular pressure; RNFL, retinal nerve fiber layer.
Pre/post Δ Retinal Thickness, μm
Peripapillary Sector 14-day HDTBR 70-day HDTBR
Temporal NS NS
Superior +4.69 (+2.12, +7.26) +11.50 (+7.87, +15.13)
Nasal +4.63 (+1.49, +7.76) +11.46 (+7.02, +15.90)
Inferior +4.34 (+1.97, +6.72) +10.08 (+6.72, +13.45)
Central NS NS
Data presented as mean (95% Confidence Interval). NS, non-significant.
• Statistical analyses were conducted using Stata (StataCorp LP, College Station, TX;
software version 14.0)
 Near best-corrected visual acuity
 Spherical equivalent
 Goldmann and iCare (Icare Finland Oy, Espoo, Finland) intraocular pressure (IOP)
 Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany) average retinal
nerve fiber layer thickness (RNFLT), peripapillary retinal thickness and macular
thicknesses
• LogMAR and spherical equivalent decreased during and after HDTBR (p’s < 0.001)
• Overall, iCare IOP increased during HDTBR (+1.42 mmHg, p < 0.01), but no
differences from baseline were observed post-HDTBR (p = 0.46)
• Overall, average RNFLT increased (p = 0.002), while macular
thickness decreased from baseline (p < 0.01)
• In the superior, nasal and inferior peripapillary sectors, the
magnitude of retinal thickening post-HDTBR was greater after
70-day HDTBR (p’s < 0.01):
• HDTBR induced a small non-progressive increase in IOP, which
subsided post-HDTBR
• Further research is necessary to elucidate the interaction of
HDTBR duration and the angle of tilt to study microgravity-related
ophthalmological changes Subjects remained asymptomatic throughout HDTBR
 Modified Amsler grid, red dot test, color vision, confrontational visual field were
within normal limits throughout
 No changes from baseline were detected on stereoscopic color fundus
photography
Pre/post-bed rest Spectralis OCT peripapillary retinal thickness and volume, retinal 
thickness map and color fundus photography of two sample eyes from the 14- and 
the 70-day bed rest campaigns
• HDTBR duration may be critical for replicating ophthalmological
changes observed in astronauts on ≥6-month spaceflights.
https://ntrs.nasa.gov/search.jsp?R=20150021774 2019-08-31T05:23:26+00:00Z


Comparison of Structural and Functional Ocular Outcomes Between 14- and 70-Day Bed Rest

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