Portable Autorefractors for Detecting Axial Length Changes in Space.

Area of Science:

• Space medicine
• Ophthalmology
• Biomedical engineering

Background:

• Astronauts experience significant visual changes during spaceflight.
• Portable autorefractors offer a potential solution for in-flight vision monitoring.
• Evaluating the reproducibility of these devices is crucial for accurate data collection.

Purpose of the Study:

• To assess the reproducibility of two portable autorefractors, Netra and SVOne Pro.
• To evaluate their performance in simulating spaceflight conditions (prone position with lower body positive pressure).
• To determine their suitability for monitoring longitudinal visual changes in astronauts.

Main Methods:

• Cycloplegic refractive error was measured in 13 subjects across 5 visits using both devices.
• Measurements were taken in seated and prone positions with lower body positive pressure (LBPP).
• Axial length was measured, and a user preference questionnaire was administered.

Main Results:

• SVOne Pro demonstrated slightly better intrasession reproducibility (0.37 D) than Netra (0.41 D).
• Intersession seated reproducibility was 0.67 D for SVOne Pro and 0.54 D for Netra.
• Both devices showed significant differences between seated and prone LBPP measurements; SVOne Pro was preferred and faster.

Conclusions:

• The SVOne Pro is preferred by users and is more time-efficient for refractive error assessment.
• A 0.67 D change with SVOne Pro is unlikely to occur by chance, making it sensitive to real visual shifts.
• These portable autorefractors can effectively monitor refractive changes in space, potentially inferring axial length alterations.