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⚖ Operations · PHAK Chapter 17, Aeromedical FactorsOPS-055 · 224 of 261

During a night flight, a remote pilot notices that objects viewed directly are harder to see than objects viewed slightly off-center. What explains this, and how should the pilot adjust their scanning?

AThis is caused by eye fatigue; the pilot should rest their eyes by closing them periodically
BThe center of the retina is dominated by cone cells that function poorly in low light; looking slightly off-center uses rod cells, which are more sensitive in darkness, a technique called averted vision✓
CDirect viewing is less effective at night because the pupil constricts when focused on a specific point

Why →The fovea, at the center of the retina, is packed with cone cells that require relatively bright light to function. Rod cells surround the fovea and are far more sensitive in low-light conditions. By looking approximately 10 degrees off-center from a target, the image falls on the rod-rich area of the retina, making dim objects more detectable. PHAK Chapter 17 describes this technique as averted vision.

The trap →It is counterintuitive to look away from something you are trying to see. At night, direct focus places the image on the least light-sensitive part of the retina. Slightly off-center is the correct technique.

Field note →Combine averted vision with the systematic 10-degree scanning pattern from AIM 8-1-6. At night, each segment needs a slightly longer dwell time because rod cells take a moment to register a dim target.

SOURCE → PHAK Chapter 17, Aeromedical FactorsCHECKED JUL 16ACS V.E.K6MED
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