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The CN Lantern Test and Different Viewing Distances.

Ali Almustanyir, Jeffery K Hovis1

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Optometry and Vision Science : Official Publication of the American Academy of Optometry
|May 16, 2020
PubMed
Summary
This summary is machine-generated.

Color-vision-defective individuals can identify railway signals at shorter distances. This study shows improved performance with the CN Lantern (CNLan) test at reduced viewing distances for those with red-green color vision defects.

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Area of Science:

  • Ophthalmology
  • Human Factors Engineering
  • Transportation Safety

Background:

  • Color vision defects affect railway signal interpretation.
  • Sighting distance is a critical factor in signal visibility for employees.
  • Standard color vision tests may not reflect real-world railway yard conditions.

Purpose of the Study:

  • To evaluate the performance and repeatability of the CN Lantern (CNLan) test in color-normal and color-deficient individuals at varying viewing distances.
  • To determine if reduced sighting distances improve signal identification for color-vision-defective individuals.
  • To assess the suitability of the CNLan test for simulating railway signal identification in different operational contexts.

Main Methods:

  • 56 color-normal and 63 color-deficient subjects participated.
  • The CNLan test was administered at 4.6, 2.3, 1.15, and 0.57 m viewing distances.
  • Test-retest repeatability was assessed after 10 days.

Main Results:

  • Color-normal subjects passed all tests without errors.
  • Color-deficient subjects' pass rate increased from 12% at 4.6 m to 62% at 0.57 m.
  • The CNLan test demonstrated very good repeatability (AC1 > 0.85) for the color-vision-defective group.

Conclusions:

  • Improved performance at shorter distances is likely due to increased retinal illumination.
  • Shorter sighting distances, typical in railway yards, significantly enhance signal identification for color-deficient individuals.
  • Approximately 62% of individuals with red-green color vision defects may correctly identify signals in railway yards with sighting distances under 100 m.