What happens to vision at altitudes above 5,000 feet MSL?

At altitudes above 5,000 feet Mean Sea Level (MSL), the decrease in night vision can be attributed largely to several physiological factors that affect the human body in a lower-oxygen environment. As altitude increases, the partial pressure of oxygen decreases, which can lead to hypoxia—or decreased oxygen availability to tissues. The retina is particularly sensitive to oxygen levels, and insufficient oxygen can impair the function of rods, which are the photoreceptor cells responsible for vision in low-light conditions.

Additionally, the body may experience other changes at elevated altitudes, such as changes in visual acuity and perception due to lower atmospheric pressure and potential dehydration, which can influence sharpness and clarity of vision. This reduction in night vision capabilities is important for flight paramedics, who may need to make critical decisions in low-light conditions. Understanding these effects is vital for safe operation and patient care in airborne medical situations.

The other options do not accurately reflect the physiological changes that occur with increased altitude.