Color Vision Deficiency and the X-Chrom Lens Notes

Use of colored filters to address color deficiency first proposed by Seebeck (1837).
Zeltzer granted a patent for the X-Chrom lens in 1971.
The X-Chrom lens is a red contact lens worn unilaterally (on one eye).

Siegel stated the lens does not correct color vision but aids color naming by making shorter wavelengths less intense than longer wavelengths.
Improvements in performance are primarily seen in pseudoisochromatic plate tests (e.g., Ishihara Plate Test).
Enhances performance by increasing contrast/relative luminance between figures and backgrounds rather than correcting the underlying biological deficiency.
Most effective for anomalous trichromats; not effective for tritans.

Kassar et al.: Found no statistically significant improvement in performance on the Farnsworth-Munsell 100-hue test, wire matching test, or Farnsworth Lantern test.
Welsh et al. (1979): Study at the Federal Aviation Administration Civil Aeromedical Institute showed color-deficient subjects averaged 8.1 out of 18 correct at $6\,m$ in dim light, compared to zero errors by normal subjects.
Paulson: Severe protanomalous trichromats performed worse on the Farnsworth Lantern and Dichromatous-15 tests when using the lens.
Matsumoto et al.: Reported performance was unchanged or worse on Pickford-Nicolson red-green anomaloscope tests.

Visual Acuity: Welsh et al. found a significant decrement $(p < 0.05)$ in visual acuity in the eye wearing the X-Chrom lens.
Pulfrich effect: A distortion of depth perception caused by visual latency when a filter is placed over one eye. Heron et al. and Landrigan noted this effect in subjects; $60\%$ of subjects in Matsumoto's study reported decreased depth perception.
Additional symptoms include blurring, "light dazzlement," and difficulty with rapid color discrimination.

No evidence supports the use of X-Chrom lenses as an accommodative aid for safety-critical roles.
Transportation industry roles (e.g., locomotive engineers, air traffic controllers) require rapid, accurate color identification that the lens cannot provide.
Recommended for use only in occupations where color accuracy is a relative requirement and external cues (labels, consistent signal patterns) are available.