Oxygenation state and mesopic sensitivity to dynamic contrast stimuli

Area of Science:

• Ophthalmology
• Aerospace Medicine
• Human Physiology

Background:

• Photoreceptor oxygen consumption increases in dim light, potentially causing outer retinal hypoxia.
• Night flying involves low photopic and mesopic light levels, where visual performance is critical.

Purpose of the Study:

• To investigate the impact of varying oxygenation states on visual sensitivity.
• To assess the susceptibility of the outer retina to hypoxia under conditions relevant to night aviation.

Main Methods:

• Frequency doubling perimetry was used to measure threshold sensitivity.
• Participants breathed mild hypoxia (14.1% O2), hyperoxia (100% O2), or normoxia (air).
• Testing occurred at low photopic (10 cd/m2) and mesopic (1 cd/m2) luminance levels.

Main Results:

• At 10 cd/m2, 100% oxygen marginally enhanced sensitivity.
• At 1 cd/m2, hypoxia consistently reduced sensitivity, while hyperoxia improved it across all retinal locations.
• Results suggest oxygen-dependent visual performance at mesopic luminance.

Conclusions:

• Oxygenation state significantly affects mesopic visual sensitivity, beyond changes in retinal illumination due to pupil size.
• Findings support the hypothesis that the outer retina (photoreceptors) is susceptible to hypoxia during twilight viewing.
• This has implications for visual performance and safety in aviation environments with low light conditions.