Empiric determination of corrected visual acuity standards for train crews

Probably the most common visual standard for employment in the transportation industry is best-corrected, high-contrast visual acuity. Because such standards were often established absent empiric linkage to job performance, it is possible that a job applicant or employee who has visual acuity less than the standard may be able to satisfactorily perform the required job activities. For the transportation system that we examined, the train crew is required to inspect visually the length of the train before and during the time it leaves the station. The purpose of the inspection is to determine if an individual is in a hazardous position with respect to the train. In this article, we determine the extent to which high-contrast visual acuity can predict performance on a simulated task.

Performance at discriminating hazardous from safe conditions, as depicted in projected photographic slides, was determined as a function of visual acuity. For different levels of visual acuity, which was varied through the use of optical defocus, a subject was required to label scenes as hazardous or safe.

Task performance was highly correlated with visual acuity as measured under conditions normally used for vision screenings (high-illumination and high-contrast): as the acuity decreases, performance at discriminating hazardous from safe scenes worsens.

This empirically based methodology can be used to establish a corrected high-contrast visual acuity standard for safety-sensitive work in transportation that is linked to the performance of a job-critical task.