Predicting the CN Lantern Test for Railways with Clinical Color-vision Tests

Area of Science:

• Ophthalmology
• Occupational Health
• Vision Science

Background:

• Color vision deficiency (CVD) impacts career options, particularly in safety-critical roles like Canadian railways.
• The CN Lantern (CNLan) test is used by railway medical units, but its correlation with standard clinical color vision tests (CCVTs) is not well-established.
• Accurate prediction of CNLan performance is crucial for clinicians advising patients with CVD.

Purpose of the Study:

• To evaluate the predictive ability of various CCVTs for performance on the CNLan test.
• To provide guidance to clinicians for career counseling of individuals with CVD in the railway industry.

Main Methods:

• The study involved 56 normal-color-vision and 63 CVD subjects.
• The CNLan test viewing distance was systematically varied.
• Multiple CCVTs were administered, including Hardy, Rand, and Rittler (HRR), Ishihara, ColorDx PIP, Rabin Cone Contrast Test, CAD, Cambridge, USAFOBA, Farnsworth Munsell D15, and ColorDx D15.

Main Results:

• Failure on the Farnsworth Munsell D15 or ColorDx D15 strongly predicts failure on the CNLan at a 4.6m distance.
• The agreement between CCVTs and CNLan performance decreased as the viewing distance for the CNLan test was reduced.

Conclusions:

• For locomotive engineer roles, clinicians should use the HRR or ColorDx PIP combined with a D15 test to counsel patients.
• For yard positions, a mild-to-moderate CVD classification on HRR or ColorDx PIP suggests a high likelihood of passing the CNLan test.