Purchase this article with an account.
Ali Almustanyir, Jeffery K Hovis; Predicting the CN Lantern Test for Railways with clinical color vision tests.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5404.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Sighting distances for railway signal lights can vary so that individuals with a color vision defect (CVD) who do not qualify for positions requiring longer sighting distances may qualify for positions using shorter sighting distances. However, there is little information available as to whether clinical color vision tests can predict who will be able to identify correctly signal light colors at various distances. This study determines the ability of 3 clinical color vision tests to predict signal light identification at different viewing distances.
The CN Lantern (CNLan) was used to simulate railway signal lights. Viewing distance was varied between 4.6m and 0.57 m using a geometric progression. The 4.6 m viewing distance is equivalent to a sighting distance of about 0.8 km. The clinical color vision tests were the ColorDx Diagnosis Plates (ColorDx), Farnsworth D15 (D15) scored as pass-fail and the Cone Contrast Sensitivity Test (CCST) using the lowest sensitivity value. Thirty-five CVD subjects participated in this study.
The average number of errors on CNLan decreased with decreased viewing distance with the pass rate increasing from 12% at 4.6 m to 62% at 0.57 m. The predictive values of the 3 tests for failing CNLan at 4.6 m and 2.3 m distances were greater than 95%. At the two closer distances of 1.15 m and 0.57 m, the predictive values for failing decreased to approximately 80% for the D15, 65% for the ColorDx and 52% for the CCST. The predictive values for passing at the two furthest distances were approximately 25% for the D15, 33% for the ColorDx, 45% for the CCST. The predictive values for passing the CNLan at 1.15 m and 0.57 m distances were approximately 92% for the D15, 100% for the ColorDx, and 75% for the CCST
The high predictive values for failing and relatively low predictive values for passing the CNLan at the longer viewing distances indicated that identifying railway signal lights at longer distances was challenging for CVD individuals. Most CVD subjects will fail. At the closer distances, individuals with a mild to moderate defect could identify the signal lights correctly. Passing the D15 or a score that is less than severe on the ColorDx were excellent predictors of who will pass at the closer distances. However, all 3 tests were too sensitive to predict adequately failures at the closer viewing distances.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
This PDF is available to Subscribers Only