Colour Vision defects

Question 1

What is anomalous trichromacy?

Answer 1

Impairment of normal colour vision where one of the cones is altered (defected) in its spectral sensitivity

Question 2

In the deficiency protanomaly what mechanism and characteristics do they inherit?
which cones are affected?
what is the inheritance pattern?
and what is the prevalence?

Answer 2

1. Reduced sensitivity to red light due to defective L (red) cone pigment May confuse white with green and confuse reds, yellows and greens but loss of colour discrimination varies greatly between individuals. Reduced sensitivity to red light.
2. RED
3. X linked recessive
4. 1.08% of the population, 1% in Men and 0.03% in Women

Question 3

In the deficiency Deuteranomaly what mechanism and characteristics do they inherit?
which cones are affected?
what is the inheritance pattern?
and what is the prevalence?

Answer 3

1. Reduced sensitivity to green light due to defective M (green) cone pigment May confuse white with green and confuse reds, yellows and greens but loss of colour discrimination varies greatly between individuals.
2. Green
3. X linked recessive
4. 4.63% in the population 5% in Men 0.03% in Women

Question 4

In the deficiency Tritanomaly what mechanism and characteristics do they inherit?
which cones are affected?
what is the inheritance pattern?
and what is the prevalence?

Answer 4

1. Reduced sensitivity to blue light due to defective S (blue) cone pigment Loss of colour discrimination for blues, blue – greens and greens.
2. Blue
3. autosomal dominant
4. 1 in 500 very rare

Question 5

What is the prevalence of protanopia?

Answer 5

1.01% in the population, 1% in men, 0.01% in Women

Question 6

what is the prevalence of deutanopia?

Answer 6

1.27% in the population, 1% in men, 0.01% in Women

Question 7

What is Kollner’s rule? what conditions do not follow this rule?

Answer 7

This rule states that outer retinal diseases and media changes result in blue-yellow color defects, while diseases of the inner retina, optic nerve, visual pathway, and visual cortex will result in red-green defects.

There are exceptions to Köllner’s rule, notably glaucoma, which is an optic nerve disorder, and is usually associated with blue-yellow defects in the initial phase, following which red-green defects later develop.

Question 8

What does a Nagle Anomaloscope differentiate between?

Explain the test and findings

Answer 8

Differentiates between

• Dichromats and anomalous trichromats
• Dichromats; all yellow intensities are matched
• Anomalous trichromats; range of matches reflects severity
• Protanopes have more red
• Deutanopes have more green
• Normal finds only one match
• Tritanopia not tested

Question 9

What is a Ishihara test?
Explain the test ad findings?
what type of plates are there?

Answer 9

Colour Discrimination

• Standard illuminant C
• 38 plate test (or 24)
• 1plateperpage
• 2demonstration/malingerer plates
• Positive plates, ie sees alternative number
• False negative plates, ie sees nothing
• 4 false positive plates, ie sees #
• 4 plates, differentiate Protan/Deutan
• 12 plates with lines
• To pass 24 plate ishihara, you can misread only 2 or less
• To pass 38 plate ishihara, you can misread only 3 or less

For occupational testing, if a patient fails the Ishihara, review the city university test or the D15

Question 10

What does the D15 saturated and desaturated test for?

what would a protan, deutan and tritan result look like?

Answer 10

D15 (Saturated and Desaturated)

Colour Matching

• Selection from Farnsworth
• Desaturated = increased sensitivity
• Discs are numbered on reverse
• The 15 Caps are orientated on the CIE Chromaticity diagram to emphasise the colour confusion for the three deficiencies (Protan, Deutan and Tritan)

Question 11

What is possible management/ counselling for a colour deficient patient?

Answer 11

• Chromagen lenses (although limitations)

o Enhances colour perception rather than treating CVD

§ Shifts the wavelength of light that the individual can now see

o Cannot be used during CV testing for occupational purposes

• Genetic Counselling

o Although there is no cure for this condition, genetic counselling can indicate the chances for a CVD being passed on to the patient’s children

· Can prepare for such outcome