Clinical and Occupational Applications of Colour Vision Testing

Rationale for Colour Vision Testing in Optometric Practice

• Congenital Defects (often tested using the Ishihara test):

  • Routine Testing: Optometrists should perform colour vision tests routinely if the patient has not been seen previously for this evaluation.
  • Vocational and Daily Living Advice: Testing allows the practitioner to offer informed advice regarding career paths and navigation of daily life tasks affected by colour perception.
  • Pediatric Considerations: Early testing in children is essential to inform teachers and parents of any deficiencies, allowing for educational accommodations.
  • Occupational Reports: Practitioners must complete official reports for potential employers or regulatory bodies.
  • Baselines: Establishing a baseline is critical to differentiate between existing congenital defects and a newly acquired defect in the future.

• Acquired Defects (often tested using the City University test):

  • Symptom-Driven Testing: Testing is required when a patient presents with suspicious signs or symptoms indicative of pathology.
  • Early Detection: In many pathological conditions, changes in colour vision often precede detectable changes in visual acuity or visual field patterns.
  • Pathophysiological Separate Pathways: The visual system utilizes distinct pathways for colour versus achromatic information, and for Red-Green ($R-G$) versus Blue-Yellow ($B-Y$) signals.
  • Differential Diagnosis: Identifying whether a defect is $R-G$ or $B-Y$ can aid in the differential diagnosis and enhance the understanding of the specific disease progression.
  • Treatment Outcomes: Early detection of acquired defects can facilitate earlier medical intervention and treatment.

Screening Tests for Colour Vision

• The Preliminary Sieve:

  • Screening tests serve as an initial filter to determine if more comprehensive diagnostic testing is required.

• Essential Criteria for Screening Tools:

  • Speed and availability.
  • Simplicity for both the patient and the tester.
  • High sensitivity and specificity.
  • Suitable for use by non-specialist testers.

• Testing Conditions:

  • Despite their simplicity, illumination and viewing conditions must be strictly controlled to ensure valid results.

• The Ishihara Test:

  • This test is widely utilized as it fulfills the screening requirements, specifically for identifying Red-Green colour vision deficiencies.

Occupational Guidance and Formal Standards

• Determining Standards:

  • Practitioners must determine if formal standards exist via the regulating or licensing authority (check if standards are national or local).
  • Employer resources should be consulted, such as the Association of Optometrists (AOP) Members Handbook (found at www.aop.org.uk under "Vision Standards").

• Literature References for Occupational Standards:

  • Work and the Eye by RV North, Butterworth Heinemann, Second Edition, $2001$.
  • Diagnosis of Defective Colour Vision by J Birch, Butterworth Heinemann, Second Edition, $2001$.

• Execution of Occupational Testing:

  • The optometrist must use the EXACT test prescribed by the regulating body.
  • Precise adherence to pass/fail criteria is mandatory. These cut-offs vary significantly by profession:
    • Firefighters: Failing to correctly identify $\ge 3$ plates results in a fail.
    • Pilots: Missing any plates results in a fail (though this usually triggers secondary, more advanced testing).
  • Reporting: Practitioners must identify the specific reporting format (e.g., specific forms) and the exact information required by the employer.

Managing Test Integrity and Clinical Aids

• Prevention of Cheating:

  • Practitioners should be prepared for subjects attempting to cheat on colour vision tests. A primary countermeasure is to mix the order of plate presentation.

• Clinical Checks:

  • The optometrist must explicitly check that the patient is not wearing coloured contact lenses, such as X-CHROM lenses, during the test.

• The Role of Red Filters:

  • In individuals with deuteranopia (a type of red-green defect), a red filter can assist in discriminating patterns. This works by altering the brightness/contrast of the target relative to the background, allowing the subject to see patterns that would otherwise be invisible to them.

Implications for Driving and Road Safety

• Accident Rates:

  • There is evidence suggesting a higher accident rate among those with colour vision deficiencies.

• Traffic Signals:

  • Generally, traffic lights are not a significant problem for these individuals.

• Specific Collision Type:

  • Congenital Colour Vision Deficiency (CCVD) is associated with a specific, predictable accident type: rear-end collisions. This is caused by a difficulty in DETECTING the appearance of red brake lights.
  • It is suggested that these accidents might be considered less serious than other types of roadway incidents, though they remain a significant concern.
  • Optometrist Responsibility: The practitioner must explain these specific risks and effects of the condition to the patient.

Longitudinal Study Data: Cumberland et al. (2004)

• The 1958 British Birth Cohort Study:

  • Participants: $12534$ children born in Great Britain in a single week.
  • Testing: Evaluated using the Ishihara test at age $11$.
  • Definition of Defect: Not reading all $24$ plates correctly (noting that this threshold may be problematic).

• Outcome Measures:

  • Education standards at ages $7$, $11$, and $16$.
  • Highest educational qualification attained by age $33$.
  • Accidents recorded both as a driver and in the workplace.

• Findings:

  • Education: No functional difference in education between those with and without CCVD. Statistically, individuals with CCVD actually performed better at age $16$, though this was not considered functionally significant.
  • Road Accidents: $8.9 \%$ of females and $19.2 \%$ of males experienced road accidents. Interestingly, those with CCVD had slightly FEWER road accidents than the general population.
  • Workplace Injuries: $30 \%$ of males experienced workplace injuries; there was no statistical difference for those with CCVD.

Summary of the Optometrist’s Professional Role

• Advice: Providing guidance on occupational requirements for specific professions and identifying limitations for everyday life.
• Programme Development: Devising or recommending suitable screening programs for specific industries and professions.
• Test Literacy: Maintaining a deep understanding of available colour vision tests and their specific clinical limitations.
• Reporting: Providing accurate, professional reports to employers and regulating bodies.
• Adaptations: Recommending and fitting adaptations, such as specialized lenses, for individuals who fail standard testing when appropriate.
• Monitoring: Conducting ongoing monitoring for employees in high-risk environments, such as monitoring for colour vision changes resulting from chemical exposure.