Advancing vision standards in aviation: Embracing evidence-based approaches

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Abstract
This study explores the relationship between visual acuity, contrast sensitivity, and pilot performance in simulated flight scenarios, including poor weather conditions, attempting to determine minimum visual requirements for safe flight. Twenty-six participants with normal or corrected-to-normal vision and varying flight experience (0-400 flight hours) completed simulated flight circuits under different weather conditions (e.g., rain, wind) using either Cambridge Simulation Glasses or defocusing lenses to degrade vision. Flight performance was assessed subjectively by an instructor using standardized criteria and objectively via simulator data. Visual acuity and contrast sensitivity were measured at each level of visual degradation. Mixed model analysis of variance revealed significant differences in the variability of vertical speed, pitch, roll, and the slope of altitude descent as a function of vision degradation level and weather conditions. There was also a significant main effect of vision degradation type (scatter or defocus) on the slope of altitude descent. Post hoc analyses indicated flight performance was first affected at 1.0 and 1.3 logarithm of the minimum angle of resolution degradation with scattering and defocusing lenses, respectively. These results suggest that current vision standards should potentially be reevaluated for them to be more based on evidence.

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