Time-limited visual resolution in pilot trainees.

Superior vision is needed for piloting aircraft in military and civilian environments. Although visual evaluations of potential pilots typically are conducted with no limit on viewing time, aviation and related occupations require superior vision under time-limited viewing conditions, and assessment of this capability is needed. The purpose of this study was to evaluate time-limited visual resolution in pilot trainees. A forced-choice letter recognition task was used to measure visual acuity (VA) and small letter contrast sensitivity (SLCS) in 37 trainees who had satisfied all vision requirements for pilot training. VA and SLCS were highly correlated (r = 0.76), indicating that the two tests measure similar aspects of visual resolution. However, although VA scores were distributed across 0.16 log units (two lines of letters on a VA chart). SLCS scores varied across 0.35 log units, which is nearly four lines on the SLCS chart. The variation in SLCS performance could be explained, in part, by subtle refractive error in pilot trainees. The results exemplify differences in performance among visually qualified trainees, and underscore the need for proper refractive correction. SLCS is a useful screening test for identifying subtle changes in vision that herald the need for optical or medical intervention.