Cromwell, R. L.

Neigut, J. S.

Taibbi, G.

Vizzeri, G.

Yarbough, P. O.

Zanello, S. B.

NASA Technical Reports Server

VISION MONITORING OF HEAD-DOWN TILT BED 
REST SUBJECTS 
RL Cromwell1, SB Zanello1, PO Yarbough1, JS Neigut2, G Taibbi3, G Vizzeri3 
1Universities Space Research Association, Houston, Texas, USA 
2National Aeronautics and Space Administration, Houston, Texas, USA 
3The University of Texas Medical Branch, Galveston, Texas, USA 
https://ntrs.nasa.gov/search.jsp?R=20110016198 2019-08-30T17:39:21+00:00Z
Vision Changes in Astronauts 
 Visual changes discovered in astronauts 
following long-duration (>6 months) spaceflight 
raised concern about ocular health during long 
duration spaceflight.  Findings include: 
 Hyperopic shifts 
 choroidal folds 
 optic disc edema 
 retinal nerve fiber layer (RNFL) thickening 
 cotton wool spots were some of the findings 
observed 
Link to Bed Rest 
 Hypotheses speculate that hypertension in the brain caused by 
cephalad fluid shifts during spaceflight is a possible mechanism 
for these ocular changes found in astronauts.   
 Head-down tilt (HDT) bed rest is a spaceflight analog that 
induces cephalad fluid shifts.   
 Previous studies of the HDT position demonstrated body fluid shifts 
associated with changes in intraocular pressure (IOP).   
 Vision monitoring of HDT bed rest subjects was implemented 
Vision Monitoring: Bed Rest 
 Vision monitoring was completed on 4 subjects participating in a 30-day 6° 
HDT bed rest study.  Of these 4 subjects, 2 received post bed rest testing 
only, and 2 received pre- and post bed rest testing.   
 Findings from 2 subjects receiving pre- and post bed rest testing  will be 
presented in detail.   
 There was no clinical evidence of choroidal folds or optic disc edema in any 
of the subjects examined.  However, in the 2 subjects receiving only post bed 
rest exams, findings from optical coherence tomography (OCT) indicated 
possible RNFL thickening.  This was difficult to determine however, without 
pre-testing information.  
Subject 1: 30-day bed rest 
 A.B. 
 25-year-old 
Caucasian male 
 General good health 
 No vision related 
complaints 
At baseline: 
 Best corrected visual acuity: 
20/20 both eyes 
 Intraocular pressure (mmHg): 
15 right eye; 14 left eye 
 Cycloplegic refraction:  
-3.25 sph +0.25 cyl ax 80 right 
eye 
-3.00 sph +0.75 cyl ax 90 left eye 
 
Ophthalmic examinations were performed at baseline, 
one day (BR+1) and 6 months (BR+180) post bed rest . 
BR+1: 
 Best corrected visual acuity: 20/20 right eye; 
20/15 left eye 
 Intraocular pressure (mmHg): 11 right eye; 10 
left eye 
 Cycloplegic refraction: 
   -3.25 sph +0.25 cyl ax 80 right eye 
   -3.00 sph +0.75 cyl ax 90 left eye 
 
 
BR+180: 
 Best corrected visual acuity: 20/20 right eye; 
20/20 left eye 
 Intraocular pressure (mmHg): 13 right eye; 14 
left eye 
 Cycloplegic refraction: 
   -3.50 sph +0.50 cyl ax 80 right eye 
   -2.75 sph +0.75 cyl ax 90 left eye 
 
 
Intraocular pressure 
0 
2 
4 
6 
8 
10 
12 
14 
16 
Baseline BR+1 BR+180 
Right eye 
Left eye 
Baseline versus BR+1 
Baseline 
BR+1 
Right eye Left eye 
Right eye Left eye 
Grey scale Total 
deviation 
 Pattern    
deviation 
Grey scale Total 
deviation 
 Pattern    
deviation 
Baseline 
BR+1 
BR+180 
Right eye 
Baseline 
BR+1 
BR+180 
Left eye 
Baseline 
BR+1 
BR+180 
Baseline BR+1 BR+180 
Left eye 
SD-OCT retinal thickness scans centered on the optic disc (20°x15°, 512 A-scans x 
19 B-scans)  
Right eye 
Baseline BR+1 BR+180 
Baseline versus BR+1 
Right eye 
Baseline versus BR+1 
Left eye 
SD-OCT for identification of 
change 
 At BR+1, SD-OCT scans showed an average increase 
in retinal thickness of 17.4 µ (+4.5%) in OD and 21.2 µ 
(+5.6%) in OS compared to baseline. However, there 
were no clinically detectable signs of optic disc edema. 
 
 At BR+180, SD-OCT measurements matched the ones 
recorded at baseline (e.g., average retinal thickness was 
389 and 388 µ at baseline and 6 month follow-up, 
respectively, in OD, while it was 378 µ in OS). 
 
 
Subject 2: 30-day bed rest 
 C.D., 27-year-old Caucasian male complained about 
blurry vision at BR+1 visit and at BR+140.  
 However, best corrected visual acuity was 20/20 in 
both eyes at all visits. 
 Cycloplegic refraction was identical at all visits and 
confirmed the presence of a slight myopia. 
 
 
 
 
 
 
 
 
Ophthalmic examinations were performed at baseline, 
BR+1 and BR+140 (at a different location). 
Intraocular pressure 
0 
2 
4 
6 
8 
10 
12 
14 
16 
18 
20 
Baseline BR+1 BR+140 
Right eye 
Left eye 
Baseline versus follow-up 
Left eye 
Summary 
 Intraocular pressure was decreased compared to baseline 
immediately post bed rest (as suggested by previous studies) 
 
 SD-OCT was able to identify subtle changes at the level of 
the optic nerve head otherwise undetected on clinical 
examination 
 
 In subject 1 structural changes somewhat correlated with 
changes seen on Standard Automated Perimetry (bilateral 
scotoma?) 
 
 In subject 1, measurements tended to return to baseline 
level at BR+180 with resolution of the scotoma 
 
Limitations 
 Only two subjects were examined pre and post bed rest.  
However, a similar trend was identified with regard to 
intraocular pressure measurements and SD-OCT 
findings for these subjects. 
 MRIs were not available.  
 Intracranial pressure was not measured/estimated. 
 Limited follow-up  
 
Conclusions 
 While subclinical changes were identified in bed 
rest subjects, findings did not replicate those 
observed in astronauts.   
 Further study of long-duration bed rest is 
needed to determine the visual consequences of 
HDT bed rest if any, and determine if HDT bed 
rest can serve as a ground based model to study 
space-related changes in vision. 


Vision Monitoring of Head-Down Tilt Bed Rest Subjects

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