LED Railway Signal Detection Rather Than Recognition is Affected by Both Refractive and Non-refractive Blur

Previous research has reported a significant effect of refractive defocus on the correct identification of red signals. The purpose of this study is to investigate the effects of both refractive defocus and non-refractive defocus (using Bangerter filters) on the perception of rail signals using the Railway LED Lantern Test (RLLT). The RLLT is the simulated practical test nominated in the Australian National Standard for Health Assessment of Railway Safety Workers.

Participants were 19-59 years old, and the best corrected visual acuity (BVCA) was required to be no worse than 6/9 binocularly. Subjects with current or active ocular conditions were excluded, and sufficiency in English was required. Best corrected refraction, visual acuity and colour vision were assessed. Participants carried out the RLLT binocularly under five conditions: best corrected, +0.50 DS, +0.75 DS and Bangerter filters 1.0 and 0.8.

Ten male and 10 female subjects completed the study; age range 20-25 and mean age 22.4 ± 1.1 years. BVCA was 6/6 (logMAR 0.0 or better). Errors occurred far more often with red than with yellow or green (p < 0.0001) and with Bangerter filter blur more than refractive blur (p < 0.0001). Failing to see a red signal, rather than misnaming the red as yellow or green, was the predominant error (p < 0.0001) and was induced far more frequently by Bangerter filters than refractive blur (p < 0.0001). This error was far more common than miscalling red as yellow (p < 0.0001) (paired t-tests).

These findings suggest that a large proportion of errors are due to not seeing the red signal rather than miscalling the red as yellow or green. Non-refractive blur was found to cause a greater increase in colour errors.