“Empty‐field myopia.” This condition usually occurs when flying above the clouds or in a haze layer that provides nothing specific to focus on outside the aircraft. This causes the eyes to relax and seek a comfortable focal distance which may range from 10 to 30 feet. For the pilot, this means looking without seeing, which is dangerous.
In other words, it is a condition in which the eyes, having nothing specific within the available visual field upon which to focus, focus automatically at a range of the order of a few metres ahead. Detection of objects outside this restricted field of view is delayed and if an object of interest does enter the restricted field of vision, the determination of its size or range would be problematic.