Oxygenation state and twilight vision at 2438 m

Area of Science:

• Ophthalmology
• Aerospace Medicine
• Human Physiology

Background:

• Hypoxia, simulating high altitude, significantly impacts vision under twilight conditions.
• Previous studies explored severe hypoxia; this research investigates milder conditions (below 8000 ft) on mesopic vision.

Purpose of the Study:

• To determine the effect of mild hypoxia on mesopic visual functions.
• To assess the benefits of supplementary oxygen on visual performance at reduced oxygen levels.

Main Methods:

• Twelve subjects were tested using Contrast Acuity Assessment, Frequency Doubling Perimeter, and Color Assessment and Diagnosis (CAD) tests.
• Visual function was assessed near sea level under normal air, mild hypoxia (15.2% oxygen, equivalent to 8000 ft), and with supplementary 100% oxygen.

Main Results:

• Oxygenation significantly affected mesopic visual parameters but not photopic.
• Mild hypoxia caused slight decrements: ~4% increase in contrast acuity thresholds, ~2 dB decrease in dynamic contrast sensitivity, and reduced chromatic sensitivity.
• Supplementary oxygen improved mesopic sensitivity.

Conclusions:

• Altered oxygenation impacts twilight vision at mesopic luminance levels, relevant for night aviation.
• Consider supplementary oxygen for critical visual tasks during flights above 8000 ft in dim light.