Colour Vision

Question 1

What are the two main theories of colour vision?

Answer 1

• Young–Helmholtz (trichromatic theory)
• Hering (opponent-process theory)

Young–Helmholtz proposes three primary colours (red, green, blue) at the photoreceptor level, while Hering proposes opponent pairs and explains afterimages.

Question 2

What are the key features of inherited colour vision defects?

Answer 2

• Present from birth
• Stable throughout life
• Can be precisely classified
• Both eyes equally affected
• Visual acuity and visual fields are normal
• Mainly red–green defects
• More common in males

These defects are typically genetic and stable over time.

Question 3

What are confusion loci?

Answer 3

Lines plotted on a CIE diagram representing colours that appear identical

In anomalous trichromats, these lines are shorter and do not span the full colour range.

Question 4

Differentiate protan, deutan, and tritan defects.

Answer 4

• Protan: defect in long wavelength (L-cone)
• Deutan: defect in medium wavelength (M-cone)
• Tritan: defect in short wavelength (S-cone)

Each defect has specific confusion points on the CIE diagram.

Question 5

What are monochromats?

Answer 5

• Individuals who see in black and white
• Either due to rods only (typical) or one cone plus rods (atypical)

They are rare and may experience reduced visual acuity, photophobia, and nystagmus.

Question 6

What are dichromats?

Answer 6

• Individuals with only two types of photopigment (one missing)
• Termed “-opias”

They perceive a limited range of colours and exhibit confusion loci.

Question 7

What are trichromats?

Answer 7

• Individuals with all three photopigments
• Colour normals are trichromats
• Anomalous trichromats have altered sensitivity

They can range from very mild to nearly as severe as a dichromat.

Question 8

What are extreme anomalous trichromats?

Answer 8

Individuals with abnormal medium and long wavelength photopigments

Their matching range on an anomaloscope extends to both sides of the normal range.

Question 9

What is the prevalence of colour vision defects?

Answer 9

• Deutan defects are most common
• Followed by protan and then tritan
• Approximately 8% of males and 0.5% of females are affected

The sex difference is due to X-linked inheritance of protan and deutan defects.

Question 10

What are the key features of acquired colour vision defects?

Answer 10

• Onset after birth
• Type and severity change over time
• Not easy to classify
• May show monocular differences
• Associated with reduced visual acuity and/or visual field defects
• More commonly blue–yellow defects

These defects affect males and females equally.

Question 11

Why is acquired colour vision deficiency difficult to classify?

Answer 11

Multiple classification systems exist

The defect can change as the underlying pathology progresses.

Question 12

What is Verriest’s classification of acquired colour vision defects?

Answer 12

• Type I: protan-like red–green defect
• Type II: deutan-like red–green defect
• Type III: tritan-like blue–yellow defect

Each type has specific characteristics regarding visual acuity and colour loss.

Question 13

What is Köllner’s rule?

Answer 13

Blue–yellow defects are associated with retinal disorders

Red–green defects are associated with optic nerve disease, with many exceptions.

Question 14

Give examples of pathologies causing acquired colour vision defects.

Answer 14

• Type I: progressive cone dystrophies
• Type II: optic neuritis
• Type III: central serous chorioretinopathy, age-related macular degeneration

Other conditions include retinal vascular disorders and glaucoma.

Question 15

What is the key difference between inherited and acquired colour vision defects?

Answer 15

• Inherited defects are present from birth
• Acquired defects develop after birth

Inherited defects are stable, while acquired defects change over time.

Question 16

What colour defect is most commonly seen in acquired conditions?

Answer 16

Blue–yellow defects

These defects often indicate retinal pathology.

Question 17

How does visual acuity differ between inherited and acquired colour vision defects?

Answer 17

• Normal in inherited defects
• Often reduced in acquired defects

This reflects the underlying pathology of acquired defects.

Question 18

How does symmetry differ between inherited and acquired colour vision defects?

Answer 18

• Inherited defects affect both eyes equally
• Acquired defects may show asymmetry

This can lead to monocular differences.

Question 19

How does progression differ between inherited and acquired colour vision defects?

Answer 19

• Inherited defects are stable
• Acquired defects change and often worsen

This is due to the underlying pathology.

Question 20

What are acquired colour abnormalities due to brain injury?

Answer 20

• Acquired achromatopsia
• Colour agnosia
• Colour anomia

These conditions are associated with damage to specific brain areas.

Question 21

What is chromatopsia?

Answer 21

A condition where vision appears tinted with a colour

Colour discrimination remains normal.

Question 22

What is cyanopsia and when does it occur?

Answer 22

Blue-tinted vision, commonly occurring after cataract removal

It can also occur as a side effect of Viagra.

Question 23

What are the different types of chromatopsia and their causes?

Answer 23

• Xanthopsia: yellow vision
• Erythropsia: red vision
• Chloropsia: green vision
• Ianthinopsia: violet vision

Each type has specific causes, often related to medications or conditions.

Question 24

What illumination is recommended for colour vision testing?

Answer 24

Illuminant C is recommended

MacBeth lamp is commonly used for tests with pigment colours.

Question 25

Why is **illumination** important in colour vision testing?

Answer 25

Different illumination sources can change the appearance of colours ## Footnote This can affect the accuracy of colour vision tests.

Question 26

What are the main types of **colour vision tests**?

Answer 26

* Pseudoisochromatic plates (e.g. Ishihara) * Hue discrimination tests (e.g. D15, desaturated D15, Farnsworth 100 hue) * Colour matching tests (e.g. anomaloscope, Medmont C100) * Colour naming tests (e.g. Farnsworth lantern, CAD) ## Footnote These tests are used to assess various aspects of colour vision.

Question 27

What tests are used to detect **colour vision defects**?

Answer 27

* Ishihara plates * Red desaturation test * City University Colour Vision test * Farnsworth F2 plate * L’anthony’s tritan album * L’anthony’s desaturated D15 * Farnsworth D15 ## Footnote These tests help identify specific types of colour vision deficiencies.

Question 28

Which tests are used to diagnose the type of **colour vision defect**?

Answer 28

* Medmont C100 * Anomaloscope * Lantern tests * CAD tests * Rabin Cone Contrast Test ## Footnote These tests help determine the specific nature and severity of colour vision defects.

Question 29

Which test measures the **severity** of colour vision defects?

Answer 29

Anomaloscope ## Footnote It provides a direct measure of the severity of colour vision deficiencies.

Question 30

Why can’t most colour vision tests measure **severity** on their own?

Answer 30

* Ishihara * Medmont C100 * Desaturated D15 * D15 * Farnsworth F2 ## Footnote These tests primarily detect or classify defects without quantifying severity individually.

Question 31

How can severity of colour vision defects be estimated **clinically**?

Answer 31

By using a sequence of tests (e.g. Ishihara followed by desaturated D15 and D15) ## Footnote This approach infers severity based on performance across multiple tests.

Question 32

What is the principle of an **anomaloscope**?

Answer 32

Colour matching, typically using the Rayleigh match (red + green = yellow) ## Footnote The subject adjusts the mixture to match a reference colour, and the range of acceptable matches is analysed.

Question 33

What alternative matches can an **anomaloscope** use?

Answer 33

* Engelking-Trendelenburg match (blue + green = blue-green) * Pickford-Lakowski match (blue + yellow = neutral grey) ## Footnote These alternative matches provide different assessments of colour vision.

Question 34

What does an **anomaloscope** assess clinically?

Answer 34

* Determines if colour vision is normal or abnormal * Identifies protan vs deutan defects * Distinguishes dichromats from anomalous trichromats * Provides a measure of severity ## Footnote It is a comprehensive tool for assessing colour vision.

Question 35

How does the **Neitz anomaloscope** work?

Answer 35

Uses specific wavelengths (yellow 589 nm, red 670 nm, green 546 nm) with two hemifields ## Footnote One hemifield has an adjustable red–green mixture, and the other has adjustable yellow luminance for matching.

Question 36

How is a **dichromat** identified on an anomaloscope?

Answer 36

They can match all red–green mixtures with a yellow luminance ## Footnote They must match both ends of the scale (e.g. 0 and 73), indicating a full matching range.

Question 37

How are **anomalous trichromats** identified using matching range?

Answer 37

* Mild cases: small matching range near normal * Moderate to severe cases: larger range that does not span the full scale * Protanomals: typically fall between 40–73 * Deuteranomals: between 0–40 ## Footnote This helps classify the severity of the defect.

Question 38

How does luminance behaviour differentiate **protan** and **deutan defects**?

Answer 38

* Deutans: luminance remains constant (horizontal line) * Protans: luminance decreases as more red is added (downward sloping line) ## Footnote This difference is crucial for understanding the nature of the defect.

Question 39

What is the **Rabin Cone Contrast Test** and what does it assess?

Answer 39

A computer-based test measuring function of each cone type separately (L, M, S cones) ## Footnote It is performed monocularly using letter recognition similar to a Bailey-Lovie chart.

Question 40

How are **lantern tests** performed?

Answer 40

Colour naming tests where one or two lights are presented for identification ## Footnote Patients must identify the colour using a limited set of names (typically red, green, white).

Question 41

Why are **lantern tests** important clinically?

Answer 41

They assess functional colour vision for real-world tasks ## Footnote Especially critical in occupations like aviation and marine navigation where distinguishing red and green lights is essential.

Question 42

How does the **Farnsworth Lantern (FALANT)** test work?

Answer 42

Presents two vertically aligned coloured lights at 8 feet for naming ## Footnote Patients must name them using only red, green, or white, with differing luminance levels to prevent brightness cues.

Question 43

What are **Holmes-Wright lanterns** and how are they used?

Answer 43

Lantern tests using signal colours with nine combinations at a distance of 6 m ## Footnote Type A (vertical lights) is used in aviation, and Type B (horizontal lights) is used in marine settings.

Question 44

What is the **CAD (Colour Assessment and Diagnosis)** test?

Answer 44

A colour vision test developed by John Barbur measuring colour discrimination thresholds ## Footnote It determines whether an individual meets safety standards for occupations such as civil aviation.

Question 45

What CAD thresholds are considered acceptable for **aviation**?

Answer 45

* Deuteranomalous subjects: thresholds < 6 SN units * Protanomalous subjects: thresholds < 12 SN units ## Footnote These thresholds ensure performance comparable to normal trichromats.

Question 46

Which occupations require **colour vision standards**?

Answer 46

* Police * Army * Navy * Airforce * Aviation * Marine occupations ## Footnote These standards are often assessed starting with Ishihara testing.

Question 47

What happens if a patient fails **Ishihara** in occupational screening?

Answer 47

Further testing is required, often with a lantern test or other assessments ## Footnote This helps determine functional colour vision.

Question 48

Which colour vision defects are typically **excluded** in occupational standards?

Answer 48

Protan defects ## Footnote Mild deuteranomalous defects may be accepted depending on the criteria.

Question 49

What are the main reasons for **colour vision standards**?

Answer 49

* Safety * Accuracy * Repeatability ## Footnote These factors are crucial for ensuring effective performance in critical roles.

Question 50

What is the **police colour vision standard**?

Answer 50

Assessed using Ishihara plates; if 3 or more errors occur, further testing is required ## Footnote This includes tests like 100 hue, D15, or Farnsworth Lantern confirmed with Medmont C100.

Question 51

What are the **armed forces colour vision categories**?

Answer 51

* CP-A: pass Ishihara or equivalent * CP-B: fail Ishihara but pass a lantern test * CP-C: fail both Ishihara and lantern tests ## Footnote These categories determine eligibility for various roles.

Question 52

Which specialties require **CP-A colour vision standard**?

Answer 52

* Army (e.g. NZSAS, CTTAG) * Navy (seamen officers and aircrew) * Air Force (engineer officers, aircraft engineering trades) ## Footnote These roles often involve critical tasks where colour vision is essential.

Question 53

What are the **Civil Aviation Authority (CAA)** requirements for colour vision?

Answer 53

Applicants must pass the Ishihara 24 plate test for a Class 1, 2, or 3 medical certificate ## Footnote Further testing includes lantern tests and additional assessments if failed.

Question 54

What happens if a candidate passes Stage 2 CAA colour vision tests?

Answer 54

A medical certificate is issued without restrictions ## Footnote This is contingent on passing specific tests like Holmes-Wright lantern or Farnsworth lantern.

Question 55

What is **Stage 3 CAA assessment**?

Answer 55

Operational Colour Vision Assessment (OCVA) conducted by a trained flight examiner ## Footnote This is a functional (non-clinical) assessment if earlier tests are not passed.

Question 56

What colour vision tasks in aviation have **no redundancy**?

Answer 56

Tasks where colour alone is critical, such as PAPI and parking lights ## Footnote These tasks require precise colour discrimination.

Question 57

What colour vision tasks in aviation have **redundancy**?

Answer 57

* Runway threshold * Centre-line * Taxiway and stopway lights * Navigation lights * Cockpit displays ## Footnote These tasks have additional cues to assist in identification.

Question 58

Can a person with **colour vision deficiency (CVD)** fly?

Answer 58

They must be able to distinguish aviation colours correctly ## Footnote If they fail, they are unfit for a Class 1 license but may obtain a Class 2 license restricted to daytime flying.

Question 59

Why is there **controversy** over colour vision standards in aviation?

Answer 59

Traditional views considered CVD unsafe due to reliance on colour ## Footnote This has been challenged, with cases showing individuals with CVD can safely perform aviation tasks.

Question 60

What are the colour vision requirements in **marine occupations**?

Answer 60

Must pass the Holmes-Wright B lantern test for roles such as Master, First Mate, Second Mate ## Footnote These standards ensure safety in navigation.

Question 61

What are the colour vision requirements for **railways and fire services**?

Answer 61

* Railways: pass Ishihara, with practical testing if failed * Tram drivers and firemen: generally have no colour vision requirements ## Footnote These standards vary based on the nature of the job.

Question 62

How is colour vision relevant in **electrical engineering**?

Answer 62

Better performance on D15 correlates with fewer errors in identifying wiring colours ## Footnote Newer systems aim to reduce reliance on colour alone.

Question 63

In which occupations is **normal colour vision** helpful?

Answer 63

* Colour matching (e.g. printers, carpets, paint) * Detecting colour changes (e.g. meat inspectors, fruit pickers) * Using colour as identifiers (e.g. pharmacist, gemologist, doctor, optometrist) ## Footnote Normal colour vision enhances performance in these roles.

Question 64

In which occupations might a **colour vision defect** be advantageous?

Answer 64

* Artists * Clothing designers ## Footnote These roles may benefit from unique perspectives offered by alternative colour perception.

Question 65

What should be included in the **history** for a full colour vision assessment?

Answer 65

* Previous knowledge of colour vision defect * Family history * Differences between eyes * Changes over time ## Footnote Ensuring the patient is not wearing coloured contact lenses is also important.

Question 66

Why is **visual acuity** important in colour vision testing?

Answer 66

Adequate visual acuity is required for accurate testing ## Footnote Lantern tests require good distance vision, while near tests may require reading correction.

Question 67

How are common clinical **colour vision tests** performed in a full assessment?

Answer 67

* Ishihara: monocular, random order * D15: monocular, repeated if failed * Desaturated D15: used if D15 is passed * Medmont C100: averaging multiple readings * OPTEC 900: binocular with distance correction ## Footnote These methods ensure comprehensive assessment.

Question 68

How is the **anomaloscope** used in assessment?

Answer 68

In inherited CVD, either eye can be tested; in suspected acquired CVD, each eye must be tested separately ## Footnote This ensures accurate diagnosis of colour vision status.

Question 69

What is the role of **CAD** and **Farnsworth-Munsell 100 Hue tests**?

Answer 69

* CAD: fast screening and certification * Farnsworth-Munsell 100 Hue test: occupational assessment of colour discrimination ## Footnote These tests are essential for evaluating colour vision in various contexts.

Question 70

What are the **testing conditions** and **pass criteria** for **Ishihara plates**?

Answer 70

* Working distance: 75 cm * Illumination: 5–600 lux (D65 or similar) * Time per plate: 3 seconds * Pass: Fewer than 4 errors ## Footnote These criteria ensure accurate assessment of color vision.

Question 71

What are the **testing conditions** and **pass criteria** for the **D15 test**?

Answer 71

* Seated desk height: 50 cm * Illumination: ≥270 lux * Time: Completed within 3 minutes * Failure: 2 or more crossings ## Footnote This test evaluates color discrimination ability.

Question 72

What are the key points for **Desaturated D15 testing**?

Answer 72

* Only performed if D15 is passed * Failure indicates anomalous trichromacy * >2 crossings suggest moderate defect * <2 crossings suggest mild defect ## Footnote This test helps identify specific types of color vision defects.

Question 73

How is the **Medmont C100** interpreted?

Answer 73

* Performed at 50 cm * Dim lighting required * At least 4 readings needed * >+1 indicates deutan defect * <−1 indicates protan defect ## Footnote This device assesses color vision defects quantitatively.

Question 74

What does the **anomaloscope** measure?

Answer 74

* Matching range of color mixtures * Mid-match point ## Footnote It is used to classify and assess the severity of color vision defects.

Question 75

What are the **testing conditions** and **pass criteria** for **lantern tests**?

Answer 75

* Conducted at 8 feet * Normally lit room * Time per presentation: 2 seconds * Pass: ≤2 errors out of 18 * Failure: >2 errors ## Footnote Lantern tests are used for assessing color recognition ability.

Question 76

How is the **Farnsworth-Munsell 100 Hue test** scored?

Answer 76

* Caps scored based on difference between adjacent cap numbers * Score of 2 considered normal ## Footnote This test evaluates color discrimination ability across a spectrum.

Question 77

What are the **testing conditions** for the **CAD test**?

Answer 77

* Conducted at 1.4 m * Dark room (lights off, door closed) * Duration: Approximately 15 minutes * Modes: Certification or fast threshold screening ## Footnote The CAD test is used for assessing color vision in various settings.