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Gianmarco Vizzeri, Bernard F. Godley; Effect Of 30-day-head-down Bed Rest On Ocular Structures And Visual Function In A Healthy Human Subject. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2995. doi: https://doi.org/.
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The effects of long-duration orbital space flights (>4 weeks) on ocular structures and visual function are largely unknown. We report the changes occurring in a healthy human subject enrolled in a study designed to duplicate the effects of a low-gravity environment.
A 26-year-old Caucasian male participated in a bed rest study conducted at the NASA Flight Analogs Research Unit. The subject was selected using the NASA standard screening procedures for bed rest studies. The study adhered to conditions as standardized for all NASA bed rest studies, including monitoring by a subject monitor and an in room camera and limited activity during bed rest. The subject spent 30 consecutive days in a 6° head-down tilt position.Ocular examinations were performed at baseline, 1 day and 6 months post bed rest. At each visit, the subject underwent a comprehensive ophthalmologic exam, including BCVA, slit-lamp biomicroscopy, Goldmann applanation tonometry, gonioscopy, dilated fundoscopic exam, optic disc stero-photography, standard automated perimetry (SAP) and SD-OCT using Spectralis OCT. SD-OCT retinal thickness scans centered on the optic disc (20°x15°, 512 A-scans x 19 B-scans) were compared at different time points using the AutoRescan feature for identification of change.
BCVA was 20/20 or better in both eyes at all visits. At one day post bed rest IOP was 11 in OD and 10 in OS (it was 15 and 14 in OD and OS, respectively, at baseline). SAP documented the presence of a bilateral symmetrical cecocentral scotoma. The 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 6 months, IOP was 14 and 15 in OD and OS, respectively, and the cecocentral scotoma had resolved. 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).
Ocular structural changes occurring after prolonged head-down bed rest can be documented using SD-OCT. Bilateral optic disc swelling, as evidenced by SD-OCT, associated with a scotoma was detected 1 day post head-down bed rest, with complete resolution observed at 6 months. These changes may be the result of cephalad shifts of body fluids in response to tilt. Further studies should clarify whether increased translaminar pressure (i.e., the difference between intracranial pressure and IOP) may be partially responsible for these findings.
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