Colour Vision defects Flashcards
What is anomalous trichromacy?
Impairment of normal colour vision where one of the cones is altered (defected) in its spectral sensitivity
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?
- 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.
- RED
- X linked recessive
- 1.08% of the population, 1% in Men and 0.03% in Women
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?
- 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.
- Green
- X linked recessive
- 4.63% in the population 5% in Men 0.03% in Women
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?
- Reduced sensitivity to blue light due to defective S (blue) cone pigment Loss of colour discrimination for blues, blue – greens and greens.
- Blue
- autosomal dominant
- 1 in 500 very rare
What is the prevalence of protanopia?
1.01% in the population, 1% in men, 0.01% in Women
what is the prevalence of deutanopia?
1.27% in the population, 1% in men, 0.01% in Women
What is Kollner’s rule? what conditions do not follow this rule?
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.
What does a Nagle Anomaloscope differentiate between?
Explain the test and findings
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
What is a Ishihara test?
Explain the test ad findings?
what type of plates are there?
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
What does the D15 saturated and desaturated test for?
what would a protan, deutan and tritan result look like?
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)
What is possible management/ counselling for a colour deficient patient?
• 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
