Ocular Outcomes Comparison Between 14- and 70-Day Head-Down-Tilt Bed Rest

Area of Science:

• Ophthalmology
• Aerospace Medicine
• Physiology

Background:

• Microgravity exposure during spaceflight can cause ocular changes.
• Head-down-tilt bed rest (HDT BR) is used to simulate some effects of microgravity.
• Understanding the impact of HDT BR duration on ocular health is crucial for astronaut safety.

Purpose of the Study:

• To compare ocular outcomes in healthy subjects undergoing 14-day versus 70-day head-down-tilt bed rest.
• To investigate the influence of HDT BR duration on visual acuity, intraocular pressure, and retinal structure.

Main Methods:

• Healthy subjects underwent 14-day and/or 70-day 6° HDT bed rest.
• Ophthalmologic examinations included visual acuity, intraocular pressure (IOP), and Spectralis OCT retinal imaging.
• Mixed-effects linear models compared pre- and post-HDT BR ocular parameters between the two study durations.

Main Results:

• No significant differences in most ocular outcomes between 14- and 70-day HDT BR.
• Greater peripapillary retinal thickening was observed in the 70-day HDT BR group compared to the 14-day group.
• A small increase in IOP occurred during HDT BR, which subsided post-rest.

Conclusions:

• Seventy-day HDT BR induced more significant peripapillary retinal thickening than 14-day HDT BR.
• Spectralis OCT detected retinal nerve fiber layer thickening, indicating optic disc swelling without clinical edema.
• HDT BR duration may be critical for simulating microgravity-induced ophthalmologic changes in astronauts.